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posted on 25 September 2017

September 25, 2017 Weather and Climate Report

Written by Sig Silber

Things are starting to come back towards normal. The weather pattern for the next ten days or so may be "fairly amplified" meaning strong Highs and Lows but that pattern is expected to change from very meridional to much more zonal in the latter part of the 6 to 14 Day Forecast Period. We expect much less tropical cyclone activity.


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We have been publishing daily and more frequent updates on tropical storms. To keep the commentary up to date has meant republishing the articles daily which changes the URL. So to find them if you have an interest, the best way is to go to the Directory and click on the top link. Saturday we published our Three to Four Season Outlook and compared the forecasts of NOAA and JAMSTEC for the first three seasons namely Fall, Winter, and Spring. This report can be accessed here.


For those who do not wish to  read that full report, here is a summary.

  NOAA Alaska Plus CONUS JAMSTEC North America JAMSTEC Europe

NOAA OND

JAMSTEC

SON

Temp

OND US Temperature Issued on September 21, 2017, NOAA Forecast SON Temperature Based on Sep 1, 2017 JAMSTEC Forecast SON Europe Temperature JAMSTEC Sep 1, 2017 Forecast

DJF

2017/2018

Temp

DJF 2017 0 2018 US Temperature Issued by NOAA on September 21, 2017 DJF NA Temperature based on JAMSTEC Sep 1, 2017 Forecast DJF 2017 - 2018 Europe Temperature based on JAMSTEC Sep 1, 2017 Forecast

MAM 2018

Temp

MAM 2018 Temperature Issued by NOAA on September 21, 2017 MAM NA Temperature based on Sep 1 JAMSTEC Forecast MAM 2018 Europe Temperature Based on Sep 1, 2017 Jamstec Forecast

 

There are changes period to period in the NOAA Temperature Outlook as the EC area grows and the warmer than climatology area shrinks. For JAMSTEC, North America is much colder than in the NOAA forecasts especially during the winter of 2017/2018 and much of Europe has a cool winter. The impact on energy prices is very different with the two forecasts.

Precipitation

  NOAA Alaska Plus CONUS JAMSTEC North America JAMSTEC Europe

NOAA OND

JAMSTEC

SON

Precip

SON US Precipitation Issued by NOAA on September 21, 2017 SON 2017 NA Precipitation Based on Sep 1, 2017 JAMSTEC Forecast SON Europe JAMSTEC Precipitation Sep 1, 2017 Forecast

DJF

2017/2018

Precip

NOAA DJF Precipitation Issue on September 21, 2017 DJF NA Precipitation based on JAMSTEC Sep 1, 2017 Forecast DJF 2017 - 2018 Europe Precipitation based on JAMSTEC Sep 1, 2017 Forecast

MAM 2018

Precip

MAM 2018 Precipitation issued by NOAA on September 21, 2017 MAM US Precipitation based on Sep 1, JAMSTEC Forecast MAM 2018 Europe Precipitation Based on Sep 1, 2017 Jamstec Forecast

 

For NOAA, Fall and Winter have a typical La Nina pattern. JAMSTEC basically agrees for Fall and Winter but has a more eastern (Northeast) precipitation pattern for North American in the Winter and does not have a dry Southeast for this Fall. JAMSTEC has a dry forecast for CONUS in the Spring of 2018 compared to a mostly EC forecast by NOAA which has a wet North Central area that includes the Great Lakes. Europe is dry for all three seasons. I think you can see Iran in those maps and it is dry in the Winter and next Spring. Afghanistan also.

A. Now we focus on Alaska and CONUS (all U.S.. except Hawaii)

First Let us focus on the Current (Right Now to 5 Days Out) Weather Situation.

Water Vapor.

This view of the past 24 hours provides a lot of insight as to what is happening.

Eastern Pacific Animation

Below is the same graphic as above but without the animation to show the current situation with respect to water vapor imagery for North America. It also covers more of CONUS.

Water Vapor Imagery

Tonight, Monday evening September 25, 2017, as I am looking at the above graphic, you can see Maria. You can see Pilar. You see the stream of moisture that has been flowing through Texas.

Looking at the current activity of the Jet Stream.

Not all weather is controlled by the Jet Stream (which is a high altitude phenomenon) but it does play a major role in steering storm systems especially in the winter The sub-Jet Stream level intensity winds shown by the vectors in this graphic are also very important in understanding the impacts north and south of the Jet Stream which is the higher-speed part of the wind circulation and is shown in gray on this map. In some cases however a Low-Pressure System becomes separated or "cut off" from the Jet Stream. In that case it's movements may be more difficult to predict until that disturbance is again recaptured by the Jet Stream. This usually is more significant for the lower half of CONUS with the cutoff lows being further south than the Jet Stream. Some basic information on how to interpret the impact of jet streams on weather can be found here and here.

Current Jet Stream

One sees the current jet stream above. You can see the trough that is for sure. You might even be able to visualize how the lower part of that trough might split off and become a closed Low.


Source

The above shows the geography of the Great Basin which is the route that winter storms take. The storm is pinned between the Sierra Nevada and Rocky Mountains. This explains why these troughs are so common.  It also explains why points north get more precipitation than points south. These troughs have a long distance to travel/extend before the can impact the Southern Tier.

This graphic [it is was updating which it is not currently] provides a good indication of where the moisture is. It is a bit different than just moisture imagery as it is quantitative.

 Center for Western Weather and Water Extremes, Scripps/UCSD.

This graphic is about Atmospheric Rivers i.e. thick concentrated movements of water moisture. More explanation on Atmospheric Rivers can be found by clicking here or if you want more theoretical information by clicking here. The idea is that we have now concluded that moisture often moves via narrow but deep channels in the atmosphere (especially when the source of the moisture is over water) rather than being very spread out. This raises the potential for extreme precipitation events. This evening we see (a graphic that is not updating properly).

You can convert the above graphic in to a flexible forecasting tool by clicking here. One can obtain views of different geographical areas by clicking here.

Day One CONUS Forecast

Day 1 Forecast Map

Day Two CONUS Forecast

Day 2 Forecast

Again you see what is going on in Texas which is serious.

60 Hour Forecast.Animation

Here is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. Beyond 60 hours, additional maps are available at links provided below.

current highs and lows

The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color coding.

Tropical Activity

Eastern Pacific Two Day Tropical Weather Outlook

When there is activity and I have not provided the specific links to the storm of "immediate" interest, one can obtain that information at this link. At this point in time, no (new) tropical events are expected to appear in this graphic during the next 48 hours. If that changes, we will provide an update. Information on Maria and Pilar can be found by going to the Directory and clicking on the top link that is a hurricane update. .

Below is a graphic which highlights the forecasted surface Highs and the Lows re air pressure on Day 3. The Day 6 forecast can be found here.  I used to present the Day 3 with a link to Day 6 but showing Day 6 may be more useful. [But this week I am showing the Day 3 because the Day 6 Image right now is not working}

Day 3 Weather Forecast

When I look at this Day 3 forecast, there is a low over Alaska but impacting much of Canada having a surface central pressure of 1000 hPa. East of Kamchatka off the tip of the Aleutioans there is a High with a surface pressure of 1028 hPa. West of Kamchatka there is another Low with central surface pressure of 992 hPa. Since the two Lows are separated by a High this is not a split Aleutian Low but something else. The High Pressure off of the West Coast, the familiar RRR or more properly called the Eastern Pacific Semi-tropical High or the Hawaiian High, is further north than in the Summer and has a surface central pressure of 1016 hPa. This configuration normally would make it somewhat difficult for precipitation entering from the Pacific to directly reach the Northwest but allow storms off the coast of Mexico to move north and impact CONUS that way. But if you look closely at the Aleutian Low it extends to the south quite a bit so that it can direct moisture in the Washington State and Oregon.

You can see Maria in this graphic but out to sea and just barely impacting CONUS on Day 3. There is also a huge High over the mid-Rockies. One might conclude that the Low northeast of Maria is Lee.

I provided this K - 12 write up that provides a simple explanation on the importance of semipermanent Highs and Lows and another link that discussed possible changes in the patterns of these highs and lows which could be related to a Climate Shift (cycle) in the Pacific or Global Warming. Remember this is a forecast for Day 6. It is not the current situation.

Now looking at the Day 5 Jet Stream Forecast.

Jet Stream Five Days Out .

This is a Day 5 forecast by one model. If you look at the sub-critical arrows you can see the flow from Mexico into CONUS especially Texas. You might even be able to detect Maria and see the trought that is forcing Maria to turn out to sea.

Putting the Jet Stream into Motion and Looking Forward a Few Days Also

To see how the pattern is projected to evolve, please click here. In addition to the shaded areas which show an interpretation of the Jet Stream, one can also see the wind vectors (arrows) at the 300 Mb level.

This longer animation shows how the jet stream is crossing the Pacific and when it reaches the U.S. West Coast is going every which way.

When we discuss the jet stream and for other reasons, we often discuss different layers of the atmosphere. These are expressed in terms of the atmospheric pressure above that layer. It is kind of counter-intuitive to me. The below table may help the reader translate air pressure to the usual altitude and temperature one might expect at that level of air pressure. It is just an approximation but useful.

air pressure and altitude Re the above, H8 is a frequently used abbreviation for the height of the 850 millibar level (which is intended to represent the atmosphere above the Boundary Layer most impacted by surface conditions), H7 is the 700 mb level, H5 is the 500 mb level, H3 is the 300 mb level. So if you see those abbreviations in a weather forecast you will know what they are talking about.

Click here to gain access to a very flexible computer graphic. You can adjust what is being displayed by clicking on "earth" adjusting the parameters and then clicking again on "earth" to remove the menu. Right now it is set up to show the 500 hPa wind patterns which is the main way of looking at synoptic weather patterns. This amazing graphic covers North and South America. It could be included in the Worldwide weather forecast section of this report but it is useful here re understanding the wind circulation patterns.

You can enlarge the below daily (days 3 - 7) weather maps for CONUS by clicking on Day 3 or Day 4 or Day 5 or Day 6 or Day 7. These maps auto-update so whenever you click on them they will be forecast maps for the number of days in the future shown.

Short term forecasts

Here is the seven-day cumulative precipitation forecast. More information is available here.

Seven Day WPC Quantitative precipitation forecast

We see precipitation at the front of the projected trough which is really impacting Texas. And of course we see QPF where Maria is expected to be and already is.

The map below is the mid-atmosphere 7-Day chart rather than the surface highs and lows and weather features. In some cases it provides a clearer less confusing picture as it shows only the major pressure gradients. This graphic auto-updates so when you look at it you will see NOAA's latest thinking. The speed at which these troughs and ridges travel across the nation will determine the timing of weather impacts. This graphic auto-updates I think every six hours and it changes a lot. Because "Thickness Lines" are shown by those green lines on this graphic, it is a good place to define "Thickness" and its uses. The 540 Level general signifies equal chances for snow at sea level locations.Thickness of 600 or more suggests very intensely heat and fire danger.

7 Day 500 MB Geopotential Forecast

Thinking about clockwise movements around High Pressure Systems and counter- clockwise movements around Low Pressure Systems provides a lot of information.

What we see for Day 7 is West Coast Trough.  Remember this is a forecast for Day 7. Maria is not shown in this forecast. Presumable it will be gone by Day 7. The High shown just off the coast of Louisiana is significant.
Note the 540 Thickness Line re the above discussion of thickness and snow likelihood. We are not down to 540 yet so the snowline is fairly high but not so high that mountain snow is not in the forecast. Thickness lines near or over 600 tend to suggest very warm temperatures. Sometimes Meteorologists work with the 500 mb heights which provides somewhat similar readings to the "Thickness" lines but IMO provide slightly less specific information.

Four- Week Outlook

I use "EC" in my discussions although NOAA sometimes uses "EC" (Equal Chances) and sometimes uses "N" (Normal) to pretty much indicate the same thing although "N" may be more definitive.

First - Temperature

I am starting with a summary of small images of the three short-term maps. This summary provides a quick look. I could have made it so you could click and enlarge the small images but for the moment I prefer that you go past the summary for the larger versions because if I set up such links, the chances increase that you will not back out of the link properly and get lost. For most people the summary with the small images will be sufficient. Following the graphic with the three small images, you can find the larger maps and a discussion and for reference purposes I then also provide the forecast map for the current or soon to be current full month and the three-month forecast map. These are issued and updated less frequently than the first three maps shown.

Small Images of Temperature Maps

6 to 10 Days 8 to 14 Days Weeks 3 and 4
6 to 10 Day 8 - 14 Weeks 3 and 4
The above shows the progression of forecasts from six days out through four weeks out. Larger maps with discussion appear below. But this set of three maps paints a pretty good picture of what the forecast is.

 

Now the larger maps followed by a discussion that describes what is happening and any inconsistences that I see.

6 - 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 25, 2017 was 3 out of 5)

6 - 10 Day Temperature Outlook

8 - 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 25, 2017 was 2 out of 5).

8-14 Day Temperature Outlook

Looking further out.

Experimental Week 3-4 Temperature Outlook

Consolidation of 6 - 10, 8 - 14 and Experimental Week 3-4 Temperature Forecasts

Interpreted on September 25, 2017

October 2 to October 9 October 7 to October 20

Days 6 - 10: Alaska is warm to the north and west and also the Panhandle . In between it is EC which NOAA has decided they should call "Normal ". Almost half of CONUS is warm comprising the West but extending further east in the Northern Tier. Florida also is warm. A wedge shaped cool anomaly has its base in Southeastern New Mexico and Texas and trends northeast into Arkansas. The rest is EC or as part of NOAA now says is "Normal". I guess they got tired of people saying that EC meant "Equally Clueless."

Close to half half of CONUS to the west of a line running approximately from the Great Lakes southwest to the Arizona/Mexico border is warm as is Northern New England but the remainder of CONUS is EC except for a fairly large Ohio River Valley cool anomaly and a Southwest Texas cool anomaly. Alaska is warm.

The transition to the pattern shown in the Week 3 - 4 Forecast from the pattern shown in the 8-14 Day does not appear to be feasible.

Week 2: The pattern progresses east which makes the East warmer and a cool anomaly appears in the Northwest. The forecast for Alaska remains the same.

Remember the Week 3-4 Experimental Outlook was issued last Friday and I am looking at the 6 - 10 and 8 - 14 day forecasts issued today i.e. Monday. So that explains the overlap of dates. Remember that the Week 3 - 4 Forecast covers two weeks so it can appear to not mesh perfectly but actually do so over the two-week period. For all three time periods, in between the cool and warm anomalies it is usually EC i.e. the boundary is usually not sharp.

 

Reference Forecasts Full Month and Three Months.

Below is the Temperature Outlook for the month shown in the Legend. This map is first issued on the Third Thursday of the Month for the following month and then updated on the last day of the month. The 6 - 10 day and 8 - 14 Day update daily and the Week 3/4 Map Updates every Friday so usually these are more up-to-date. Note that the three maps shown at the beginning of this discussion on temperature may cover a slightly different time period since they update as the month progresses and the map below covers a particular month shown in the Legend. It is useful if one wants to understand how that month is forecast to play out.

September Early Temperature Outlook Issued on September 21, 2017

Here is the Temperature Outlook issued on the date and for the three-month period shown in the Map Legend. Again this is provided for reference only. It is the same map that is included in our Saturday night report that follows the NOAA third Thursday of the month Seasonal Outlook Update. It provides a longer time frame than the above maps. It uses a totally different methodology as it is not possible to use the dynamical models to project out three months. The dynamical models work by figuring out how the current conditions will evolve over a fairly short period of time. To look out three months or longer the approach is more statistical using the forecasted ENSO Phase and Climate Trends.

The theory behind using dynamical models for short-term forecasts (6 10 Days, 8 - 14 Days, and recently Weeks 3-4) and statistical models (Monthly and Three-Months) for longer-term forecasts makes perfect sense but sometimes we see that the short term forecasts and then the actuals do not match the statistical forecasts very well. This tells us that either the statistical forecasts were based on incorrect assumptions or that the actual weather patterns are different from what we might have expected.

OND 2017 Temperature Outlook Issued on September 21, 2017

Now - Precipitation

I am starting with a summary of small images of the three short-term maps. This summary provides a quick look. I could have made it so you could click and enlarge the small images but for the moment I prefer that you go past the summary for the larger versions because if I set up such links, the chances increase that you will not back out of the link properly and get lost. For most people, the summary with the small images will be sufficient. Following the graphic with the three small images, you can find the larger maps and a discussion and for reference purposes I then also provide the forecast map for the current or soon to be current full month and the three-month forecast map. These are issued and updated less frequently than the first three maps shown.

Small Images of Precipitation Maps

6 to 10 Day 8 to 14 Day Weeks 3 and 4
6 to 10 Day 8 - 14 Weeks 3 and 4
The above shows the progression of forecasts from six days out through four weeks out. Larger maps with discussion appear below. But this set of three maps paints a pretty good picture of what the forecast is.

 

Now the larger maps followed by a discussion that describes what is happening and any inconsistencies that I see.

6 - 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 25 was 3 out of 5)

6 - 10 Day Precipitation Outlook

8 - 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 25, 2017 was 2 out of 5)

Current 8 - 14 Day Precipitation Outlook

Looking further out.

Weeks 3 and 4 Experimental Forecast..

Consolidation of 6 - 10, 8 - 14, and Week 3-4 Precipitation Forecasts

Interpreted on September 25, 2017

October 2 to October 9 October 7 to October 20, 2017

Days 6 -10: A wedge shaped cool anomaly with the base across the central Northern Tier and then narrowing as it extends down almost to the Gulf of Mexico. The area surrounding the cool anomaly is EC and some of the edges of CONUS are wet. Most of mainland Alaska is wet with EC to the north and south including the Panhandle.

For CONUS, the extreme Southeast and a sliver of the Northwest is wet and there is a large dry anomaly centered on the Great Lakes. Alaska is dry to the North, then EC and further south including the Panhandle is wet.

The transition to the pattern shown in the Week 3 - 4 Forecast does not appear to be highly feasible. The earlier weeks seem to be progressing east fast than reflected in the Week 3 - 4 Forecast.

Week 2: As the period evolves, The Central Wedge dry anomaly widens and expands to the west further south and the small Northwest wet anomaly in the earlier period expands to the east. The East does not change much. In Alaska the dry anomaly which was in the Southeast in the first period expands to the north.

Remember the Week 3-4 Experimental Outlook was issued last Friday and I am looking at the 6 - 10 and 8 - 14 day forecasts issued today i.e. Monday. So that explains the overlap of dates. Remember that the Week 3 - 4 Forecast covers two weeks so it can appear to not mesh perfectly but actually do so over the two-week period. In between the dry and wet anomalies, it is usually EC i.e. the boundary is usually not sharp.

 

Reference Forecasts Full Month and Three Months.

Below is the Precipitation Outlook for the month shown in the Legend. This map is first issued on the Third Thursday of the Month for the following month and then updated on the last day of the month. The 6 - 10 day and 8 - 14 Day update daily and the Week 3/4 Map Updates every Friday so usually these are more up to date. Note that the three maps shown at the beginning of this discussion about precipitation may cover a slightly different time period since they update as the month progresses and the map below covers a particular month shown in the Legend. It is useful if one wants to understand how that month is forecast to play out.

October 2017 Earlyi Precipitation Outlook issued on September 21, 2017

Below is the Precipitation Outlook issued on the date and for the three-month period shown in the Map Legend. Again, this is provided for reference only. It is the same map that is included in our Saturday night report that follows the NOAA third Thursday of the month Seasonal Outlook Update. It provides a longer time frame than the above maps. It uses a totally different methodology as it is not possible to use the dynamical models to project out three months. The dynamical models work by figuring out how the current conditions will evolve over a fairly short period of time. To look out three months or longer, the approach is more statistical using the forecasted ENSO Phase and Climate Trends.

The theory behind using dynamical models for short-term forecasts (6 - 10 Days, 8 - 14 Days and recently Weeks 3-4) and statistical models for longer-term forecasts (Month and three months) makes perfect sense but sometimes we see that the short-term forecasts and then the actuals do not match the statistical forecasts very well. This tells us that either the statistical forecasts were based on incorrect assumptions or that the actual weather patterns are different from what we might have expected.

OND 2017 Precipitation Outlook Issued on September 21, 2017

Here is the NOAA discussion released today September 25, 2017

6-10 DAY OUTLOOK FOR OCT 01 - 05 2017  

TODAY'S ENSEMBLE MEAN SOLUTIONS ARE IN RELATIVELY GOOD AGREEMENT ON A FAIRLY AMPLIFIED FLOW PATTERN OVER MUCH OF THE FORECAST DOMAIN. HOWEVER, SPREAD AND UNCERTAINTY ARE HIGH AMONG THE COMPONENT ENSEMBLE MEMBERS OVER MUCH OF THE COUNTRY, ESPECIALLY IN THE WESTERN CONUS. A FAIRLY STRONG ANOMALOUS RIDGE IS  FORECAST OVER THE NORTH PACIFIC AND ALEUTIANS, AND A TROUGH IS FORECAST FROM EASTERN ALASKA TO THE NORTHWESTERN CONUS. A RIDGE IS ALSO EXPECTED TO BUILD DOWNSTREAM OVER MUCH OF THE CENTRAL AND EASTERN CONUS. THE VARIOUS SPAGHETTI MAPS (5640 AND 5820 METER LEVELS) DEPICT LARGE SPREAD AMONG THE COMPONENT ENSEMBLE MEMBERS OVER MUCH OF THE COUNTRY. TODAY'S MANUAL 500-HPA HEIGHT BLEND SLIGHTLY FAVORS THE 0Z ECMWF ENSEMBLE SOLUTION BASED PRIMARILY ON CONSIDERATIONS OF RECENT SKILL. 

THE RIDGE AND ABOVE NORMAL HEIGHT ANOMALIES OVER THE NORTH PACIFIC AND ALEUTIANS INCREASES CHANCES FOR ABOVE NORMAL TEMPERATURES FOR MUCH OF WESTERN ALASKA. THE TROUGH AND BELOW NORMAL HEIGHT ANOMALIES OVER THE PACIFIC NORTHWEST TILT THE ODDS TOWARDS BELOW NORMAL TEMPERATURES OVER WASHINGTON STATE AND PORTIONS OF THE NORTHERN INTERMOUNTAIN REGION. THE ABOVE NORMAL HEIGHT ANOMALIES OVER PART OF CALIFORNIA AND THE SOUTHWEST AND THE ABOVE NORMAL SSTS ALONG THE WEST COAST ENHANCE PROBABILITIES OF ABOVE NORMAL TEMPERATURES OVER THAT REGION. ABOVE NORMAL TEMPERATURES ARE STRONGLY FAVORED OVER THE NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LIKES AND NORTHEAST CONUS DUE TO A RIDGE AND ABOVE NORMAL HEIGHT ANOMALIES OVER THE EAST-CENTRAL CONUS. ENHANCED PROBABILITIES OF ABOVE NORMAL TEMPERATURES ARE INDICATED FOR COASTAL PARTS OF THE SOUTHEAST AND FLORIDA, DUE TO PREDICTED EASTERLY FLOW. 

THERE ARE LARGELY ENHANCED PROBABILITIES FOR ABOVE NORMAL PRECIPITATION FROM THE PACIFIC NORTHWEST TO THE UPPER MISSISSIPPI VALLEY, INCLUDING MOST OF THE ROCKIES AND GREAT PLAINS, IN ASSOCIATION WITH A TROUGH OVER THE NORTHWESTERN CONUS, AND THE POTENTIAL ADVECTION OF TROPICAL MOISTURE INTO THE REGION. BELOW NORMAL PRECIPITATION IS FAVORED FROM THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST US TO THE NORTHEASTERN CONUS DUE TO EXPECTED RIDGING. THERE ARE INCREASED ODDS FOR ABOVE NORMAL PRECIPITATION OVER FLORIDA DUE TO A PREDICTED COLD FRONT.  BELOW NORMAL SEA-LEVEL PRESSURE OVER THE BERING SEA AND THE NORTHWESTERN GULF OF ALASKA FAVORS ABOVE NORMAL PRECIPITATION OVER WESTERN ALASKA.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 3 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE MODELS AND TOOLS OVER MOST OF THE U.S.

8-14 DAY OUTLOOK FOR OCT 03 - 09 2017   

COMPARED TO THE 6-10 DAY PERIOD, THE WEEK-2 CIRCULATION PATTERN IS SIMILAR BUT MORE DEAMPLIFIED. THE WEEK-2 TEMPERATURE PATTERN IS WARMER OVERALL (ESPECIALLY IN THE SOUTH, AND IN EASTERN ALASKA) COMPARED TO THE 6-10 DAY TEMPERATURE PATTERN. THE PRECIPITATION OUTLOOK FOR THE WEEK-2 PERIOD IS EXPECTED TO BECOME MORE EAST-WEST ORIENTED (ZONAL), COMPARED TO THE 6-10 DAY PRECIPITATION OUTLOOK, WHICH IS SIGNIFICANTLY MORE NORTH-SOUTH ORIENTED (MERIDIONAL). THE SOUTHERN PLAINS AND SOUTHERN ROCKIES ARE FORECAST TO TRANSITION FROM A RELATIVELY WET 6-10 DAY PATTERN TO ONE THAT IS CLOSE TO NORMAL DURING WEEK-2.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS: BELOW AVERAGE, 2 OUT OF 5, DUE TO FAIRLY LARGE UNCERTAINTY IN TODAY'S ENSEMBLES.

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON OCTOBER 19

Some might find this analysis which you need to click to read interesting as the organization which prepares it focuses on the Pacific Ocean and looks at things from a very detailed perspective and their analysis provides a lot of information on the history and evolution of ENSO events.

Analogs to the Outlook.

Now let us take a detailed look at the "Analogs" which NOAA provides related to the 5 day period centered on 3 days ago and the 7 day period centered on 4 days ago. "Analog" means that the weather pattern then resembles the recent weather pattern and was used in some way to predict the 6 - 14 day Outlook.

Here are today's analogs in chronological order although this information is also available with the analog dates listed by the level of correlation. I find the chronological order easier for me to work with. There is a second set of analogs associated with the Outlook but I have not been regularly analyzing this second set of information. The first set which is what I am using today applies to the 5 and 7 day observed pattern prior to today. The second set, which I am not using, relates to the correlation of the forecasted outlook 6 - 10 days out with similar patterns that have occurred in the past during the dates covered by the 6 - 10 Day Outlook. The second set of analogs may also be useful information but they put the first set of analogs in the discussion with the second set available by a link so I am assuming that the first set of analogs is the most meaningful and I find it so.

Centered

Day

ENSO

Phase

PDO AMO

Other Comments

Sep 11, 1952 Neutral - +  
Oct 5, 1957 El Nino + +  
Sep 19, 1968 Neutral - - Right before an El Nino
Sep 29, 1982 El Nino - - A very strong El Nino
Sep 30, 1983 Neutral + -  
Sep 28, 1986 El Nino + - Modoki
Sep 4, 1999 Neutral N(t) -  

(t) = a month where the Ocean Cycle Index has just changed or does change the following month.

The spread among the analogs from September 4 to October 5 is 31 days again about a week more than last week. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, is about September 20. These analogs are centered on 3 days and 4 days ago (September 21 or September 22). So the analogs could be considered to be pretty much in sync with weather that we would normally be getting right now. For more information on Analogs see discussion in the GEI Weather Page Glossary.

Accounting for duplicate analogs, there are four El Nino analogs (very strange), six Neutral Analogs and zero La Nina analogs (also very strange). The phases of the ocean cycles of the analogs are consistent with all the McCabe Conditions except for McCabe Condition C which is associated with Northern Tier and and Mid-Atlantic Drought. That this one McCabe Condition has little support in the analogs provides some support for the NOAA 6 to 14 Day forecast. It is interesting that 7 out of 10 (including duplicates) analogs are associated with AMO- at the same time that we have such an active Atlantic re cyclones. Last week the analogs were associated with AMO+.

The seminal work on the impact of the PDO and AMO on U.S. climate can be found here. Water Planners might usefully pay attention to the low-frequency cycles such as the AMO and the PDO as the media tends to focus on the current and short-term forecasts to the exclusion of what we can reasonably anticipate over multi-decadal periods of time. One of the major reasons that I write this weather and climate column is to encourage a more long-term and World view of weather.

McCabe Maps modified to include the subtitles

Sometimes it is easier to work in black and white especially if you print this report so there is a black and white version from the later report by the same authors. Darker corresponds to red in the color graphic i.e. higher probability of drought.

McCabe Conditions from 2007 report with labels corrected with authors permission

McCabe Condition Main Characteristics
A Very Little Drought. Southern Tier and Northern Tier from Dakotas East Wet. Some drought on East Coast.
B More wet than dry but Great Plains and Northeast are dry.
C Northern Tier and Mid-Atlantic Drought
D Southwest Drought extending to the North and also the Great Lakes. This is the most drought-prone combination of Ocean Phases.

 

You may have to squint but the drought probabilities are shown on the map and also indicated by the color coding with shades of red indicating higher than 25% of the years are drought years (25% or less of average precipitation for that area) and shades of blue indicating less than 25% of the years are drought years. Thus drought is defined as the condition that occurs 25% of the time and this ties in nicely with each of the four pairs of two phases of the AMO and PDO.

Looking Out Beyond Three Months

The Seasonal Outlook Update Report was issued in two parts because JAMSTEC was late. Part I which focused on the NOAA forecast comparing the new forecast to the prior forecast can be accessed here and Part II which focused on the comparison between the NOAA forecast and the JAMSTEC forecast can be accessed here. The Part II report was also used to provide updates on Harvey because I can only publish two reports at the same time and be able to update them. Remember, if you leave this page to visit links provided in this article, you can return by hitting your "Back Arrow", usually top left corner of your screen just to the left of the URL box. There will be a new Seasonal Outlook issued by NOAA on September 21 which we will report on September 23.

Historical Anomaly Analysis

When I see the same dates showing up often I find it interesting to consult this list.

Recent CONUS Weather

This is provided mainly to see the pattern in the weather that has occurred recently.

Here is the 30 Days ending September 16, 2017

September 16, 2017 30 Day Temperature and Precipitation Departures

You can see the impact of Irma on Florida. You can also see the Harvey impact on Texas. Remember, this is a 30 average so the most distant seven days are removed and the most recent seven days are added.

And the 30 Days ending September 23, 2017

September 23, 2017 30 Day Temperature and Precipitation Departures

Surprisingly not much change in the precipitation picture. I had expected more. The temperature picture is changed with much less of an anomaly pattern in the eastern half of CONUS. Remember, this is a 30 average so the most distant seven days are removed and the most recent seven days are added.

B. Beyond Alaska and CONUS Let's Look at the World which of Course also includes Alaska and CONUS

Same as above but for July

I will be including the above two graphics regularly as they really help with understanding why things are happening the way they are. I think the (at least intermediate) Source is The Weather Channel and I was able to download the full presentation with difficulty and you can attempt the same thing by clicking here. I think these two slides are from a much larger set but these two really highlight the position of the Bermuda High which they are calling the Azores High in the January slide and is often called NASH and it has a very big impact on CONUS Southeast weather and also the Southwest. You also see the north/south migration of the Pacific High which also has many names and which is extremely important for CONUS weather and it also shows the change of location of the ITCZ which I think is key to understanding the Indian Monsoon. A lot of things become much clearer when you understand these semi-permanent features some of which have cycles within the year, longer period cycles and may be impacted by Global Warming. We are now at the end of September so we are half way between the set of positions shown above for July and the ones shown for January. For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant. Notice the Summer position of the Pacific High.

Forecast for Today

Temperature at 2 Meters

Notice that below the map there is a tabulation of magnitude of the current anomalies by region. From North Africa to Eastern Asia it is warmer than climatology. But Siberia is cool. CONUS is cool west and warm east.

Maine Reanalyer

This graphic is actuals not anomalies as is the case in the temperature map. We again see the dry area from North Africa through Asia other than extreme Southeast Asia but including India. South America south of the ITCZ is mostly dry. Africa north and south of the Equator and the ITCZ is mostly dry. And CONUS is also mostly dry except in the Central area.

Additional Maps showing different weather variables can be found here.

Forecast for Day 6 (Currently Set for Day 6 but the reader can change that)

World Weather Forecast produced by the Australian Bureau of Meteorology. Unfortunately I do not know how to extract the control panel and embed it into my report so that you could use the tool within my report. But if you visit it Click Here and you will be able to use the tool to view temperature or many other things for THE WORLD. It can forecast out for a week. Pretty cool. Return to this report by using the "Back Arrow" usually found top left corner of your screen to the left of the URL Box. It may require hitting it a few times depending on how deep you are into the BOM tool. Below are the current worldwide precipitation and temperature forecasts for six days out. They will auto-update and be current for Day 6 whenever you view them. If you want the forecast for a different day Click Here

Temperature

BOM Current Temperature Wedensday

Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader. Northeastern South America is surprisingly warm.

Precipitation

BOM World Preciptation  Wednesday

Notice that in the Day 6 Forecast, The Aleutian Low is not there but replaced by a High. That suggests mostly dry conditions for CONUS.

Looking Out a Few Months

Here is the precipitation forecast from Queensland Australia:

Consistently Positive SOI  forecast for September to Novermber 2017.

It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. Notice the change from the forecast last month due to a rising SOI to a consistently positive SOI. CONUS looks pretty dry except for the Northwest, Europe pretty wet. India wet, Australia wet, much of China wet.

JAMSTEC Forecasts

One can always find the latest JAMSTEC maps by clicking this link. You will find additional maps that I do not general cover in my monthly Update Report. Remember if you leave this page to visit links provided in this article, you can return by hitting your "Back Arrow", usually top left corner of your screen just to the left of the URL box.

Sea Surface Temperature (SST) Departures from Normal for this Time of the Year i.e. Anomalies

My focus here is sea surface temperature anomalies as they are one of the two largest factors determining weather around the World.

And when we look at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.[NOAA may be having problems updating their daily SST Anomaly Report so I am working with the latest version that I have]

Daily SST Anomalies

First the categorization of the SST anomalies.

Mediterranean, Black Sea and Caspian Sea Western Pacific West of North America North and East of North America North Atlantic
The Back and Caspian Seas and Persian Gulf are warm.

Cool east of Japan. 

Warm south of 30N

Cool around Baja California

Southern Hudson Bay slightly warm

Gulf of St Lawrence Warm

Great Lakes Warm

Western Caribbean Warm

Warm
The Equatorial

La Nina Cool east of Dateline and more so east of 140W. Very cool off of Ecuador and Peru

Africa West of Australia North, South and East of Australia

West of South America

East of South America

Warm off shore of West Africa.

Mixed south of Africa

Neutral

Mostly Neutral

Slightly cool south and warm southeast

Cool off of Ecuador and Peru and again south of 30S

Cool offshore of 20S to 30S.

Cool south of 40S

 

What you see in the below graphic is the change in the anomaly over the last four weeks So you have to refer to the graphic above this one to really interpret the below graphic as what we are seeing here is the change in the anomalies. So blue means a trend that is either cooler or less warm than four weeks ago. Red means a trend that is warmer or less cool than four weeks ago. So this graphic is a way of understanding how the anomalies shown in the above graphic have changed over the past four weeks. It is important to understand the distinction between these two graphics. The top one shows the recent conditions, the bottom one shows the direction of change.

September 25, 2017 four week change is SST Anomalies

The categorization of the four week change in the anomalies.

Mediterranean, Black Sea and Caspian Sea Western North Pacific West of North America East of North America North Atlantic

Black Sea and Caspian slightly warming, Mediterranean and Red Sea and Persian Gulf slightly cooling.

Mostly extreme cooling.

Cooling in the Bering Straits. and south of the Aleutians.

Warming off of British Columbia

Cooling for Baja California and in Gulf of California

Warming off of Mexico

Warming north of Nova Scotia and offshore of Newfoundland

Cooling east of CONUS (hurricanes?)

Cooling in Hudson Bay

Warming in Western Caribbean

Warming south of 50N near Greenland

Cooling British Isles

Equator Eastern Pacific Cooling East of 140W. Warming east of Somalia, Atlantic Cooling
Africa West of Australia North, South and East of Australia West of South America East of South America

Cooling along the Equator

Cooling southeast of Africa

Warming

Stable

Stable but cooling south of South America

Cooling along the Equator all the way to Gulf of Guinea off of West Africa.

Cooling south of 50S

 

It is very interesting that the entire North Pacific is showing Neutral or warm anomalies but when you look at the changes in the anomalies one gets a very different picture with many areas that are cooling (from their current temperature which is warmer than climatology).

This may be a good time to show the recent values to the indices most commonly used to describe the overall spacial pattern of temperatures in the (Northern Hemisphere) Pacific and the (Northern Hemisphere) Atlantic and the Dipole Pattern in the Indian Ocean.

Most Recent Six Months of Index Values PDO Click for full list

AMO click for full list.

Indian Ocean Dipole (Values read off graph)
October -0.68 +0.39 -0.3
November +0.84 +0.40 0.0
December +0.55 +0.34 -0.1
January +0.10 +0.23 0.0
February +0.04 +0.23 +0.2
March +0.13 +0.17 +0.0
April +0.52 +0.29 +0.2
May +0.28 +0.32 +0.2
June +0.18 +0.31 0.0
July -0.50 +0.31 0.0
August -0.68 +0.31 +0.4

 

Switching gears, below is an analysis of projected tropical hazards and benefits over an approximately two-week period.

Tropical Hazards

This graphic updates on Tuesdays and I post on Monday which is almost a week later than when this graphic was last updated. So Week Two applies at the time I write this article on Monday but by the time you read it on Tuesday, the Week Two that I am looking at is updated and becomes Week One. Mostly I see as I look at this on September 25 for what is shown as Week Two, the period September 27 to October 3, 2017, we see wet conditions* north of the Maritime Continent and over Central America but also conditions favorable* for cyclone development west of Central America. There are dry conditions* west and east of the Maritime Continent and the extreme tip of West Africa just north of the Equator.

 * Moderate Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend. ** High Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.

Now let us look at the Western Pacific in Motion.

Western Pacific Tropical Activity

The above graphic which I believe covers the area from the Dateline west to 100E and from the Equator north to 45N normally shows the movement of tropical storms towards Asia in the lower latitudes (Trade Winds) and the return of storms towards CONUS in the mid-latitudes (Prevailing Westerlies). This is recent data not a forecast. But, it ties in with the Week 1 forecast in the graphic just above this graphic. Information on Western Pacific storms can be found by clicking here. This (click here to read) is an unofficial private source but one that is easy to read.

C. Progress of ENSO

A major driver of weather is Surface Ocean Temperatures. Evaporation only occurs from the Surface of Water. So we are very interested in the temperatures of water especially when these temperatures deviate from seasonal norms thus creating an anomaly. The geographical distribution of the anomalies is very important. To a substantial extent, the temperature anomalies along the Equator have disproportionate impact on weather so we study them intensely and that is what the ENSO (El Nino - Southern Oscillation) cycle is all about. Subsurface water can be thought of as the future surface temperatures. They may have only indirect impacts on current weather but they have major impacts on future weather by changing the temperature of the water surface. Winds and Convection (evaporation forming clouds) is weather and is a result of the Phases of ENSO and also a feedback loop that perpetuates the current Phase of ENSO or changes it. That is why we monitor winds and convection along or near the Equator especially the Equator in the Eastern Pacific.

Starting with Surface Conditions.

TAO/TRITON GRAPHIC (a good way of viewing data related to the part of the Equator and the waters close to the Equator in the Eastern Pacific where we monitor to determining the current phase of ENSO. It is probably not necessary to follow the discussion below, but here is a link to TAO/TRITON terminology.

And here is the current version of the TAO/TRITON Graphic. The top part shows the actual temperatures, the bottom part shows the anomalies i.e. the deviation from normal.

Current SST and wind anomalies

Location Bar for Nino 3.4 Area Above and Below

------------------------------------------------ A B C D E -----------------

 

The pattern now is cold water to the east with cool water further west.

The below table only looks at the Equator and shows the extent of anomalies along the Equator. The ONI Measurement Area is the 50 degrees of Longitude between 170W and 120W and extends 5 degrees of Latitude North and South of the Equator so the above table is just a guide and a way of tracking the changes.The top rows show El Nino anomalies. The two rows just below that break point contribute to ENSO Neutral.

Subareas of the Anomaly

Westward Extension

 

Eastward Extension

 

Degrees of Coverage

Total

Portion in Nino 3.4 Measurement Area

These Rows below show the Extent of El Nino Impact on the Equator

1C to 1.5C (strong)

LAND

LAND

0

0

+0.5C to +1C (marginal)

LAND

LAND

0

0

These Rows Below Show the Extent of ENSO Neutral Impacts on the Equator
0.5C or cooler Anomaly (warmish neutral)

160E

DATELINE

20

0

0C or cooler Anomaly (coolish neutral)

DATELINE

160W

20

10

These Rows Below Show the Extent of La Nina Impacts on the Equator.
-0.5C or cooler Anomaly

160W

150W

10

10

-1.0C or cooler Anomaly

150W

118W

32

30

-1.5C or cooler Anomaly

118W

110W

8

0

-2.0C or cooler Anomaly

110W

105W

5

0

-2.5C or cooler Anomaly

105W

LAND

10

0

 

My Calculation of the Nino 3.4 Index

I calculate the current value of the Nino 3.4 Index each Monday using a method that I have devised. To refine my calculation, I have divided the 170W to 120W Nino 3.4 measuring area into five subregions (which I have designated from west to east as A through E) with a location bar shown under the TAO/TRITON Graphic). I use a rough estimation approach to integrate what I see below and record that in the table I have constructed. Then I take the average of the anomalies I estimated for each of the five subregions.

So as of Monday September 25, in the afternoon working from the September 24 TAO/TRITON report [Although the TAO/TRITON Graphic appears to update once a day, in reality it updates more frequently.], this is what I calculated.

Calculation of ONI from TAO/TRITON Graphic

Anomaly Segment Estimated Anomaly
  Last Week This Week
A. 170W to 160W -0.1  0.0
B. 160W to 150W -0.5 -0.3
C. 150W to 140W -0.6 -0.5
D. 140W to 130W -0.8 -0.3
E. 130W to 120W -0.7 -0.7
Total -3.1 -1.8
Total divided by five i.e. the Daily Nino 3.4 Index (-3.1)/5 = -0.6 (-1.8)/5 = -0.4

 

My estimate of the daily Nino 3.4 SST anomaly tonight is -0.4 which is a marginal La Nina value. NOAA has reported the weekly Nino 3.4 to be -0.4 which is an ENSO Neutral value. Nino 4.0 is reported the same at +0.0. Nino 3 is a bit lower at -1.0. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported much lower at -1.1 which seems more reasonable than the reading last week. It was up there close to 3 at one time so this index has been declining quite a bit and also fluctuating quite a bit which is not surprising as it is the area most impacted by the Upwelling off the coast. So it is an indication of the interaction between surface water and rising cool water. Thus it is subject to larger changes. Most likely it will be negative for a while and is negative this week but just not nearly as negative as last week. I am only showing the currently issued version of the NINO SST Index Table as the prior values are shown in the small graphics on the right with this graphic. Notice that all the indices have been declining. The same data in table form but going back a couple of more years can be found here.

Cool anomaly has shifted east this week and no longer records as La Nina.

September 25, 2017 Nino Readings

This is probably the best place to AGAIN express the thought that this way of measuring an ENSO event leaves a lot to be desired. Only the surface interacts with the atmosphere and is able to influence weather. The subsurface tells us how long the surface will remain cool (or warm). Anomalies are deviations from "Normal". NOAA calculates and determines what is "Normal" which changes due to long ocean cycles and Global Warming. So to some extent, the system is "rigged". Hopefully it is rigged to assist in providing improved weather forecasts. But to assume that any numbers reported can be assumed to be accurate to a high level of precision is foolhardy. It is strange to me that the Asian forecasting services generally conclude that that this cool ENSO Phase is not a La Nina but a near La Nina and NOAA concludes it is a La Nina. It is the same ocean. The reported readings are very close but the Asian readings are generally slightly higher (less La Nina-ish) than the NOAA reading and their cut-off points for declaring a La Nina are a bit different and the parts of the Equator they look at are a bit different. It might be explained by what part of the ENSO pattern impacts their area of geography but it just seems to me that NOAA has been a bit over eager. And I wonder why.

This overlaps with the next topic but I will show it here.

Equatorial (0 - 300) meter heat content

The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2016

Sea Surface Temperature and Anomalies

It is the ocean surface that interacts with the atmosphere and causes convection and also the warming and cooling of the atmosphere. So we are interested in the actual ocean surface temperatures and the departure from seasonal normal temperatures which is called "departures" or "anomalies". Since warm water facilitates evaporation which results in cloud convection, the pattern of SST anomalies suggests how the weather pattern east of the anomalies will be different than normal.

September 25, 2017 Equatorial Pacific SST Anomalies

A major advantage of the Hovmoeller method of displaying information is that it shows the history so I do not need to show a sequence of snapshots of the conditions at different points in time. This Hovmoeller provides a good way to visually see the evolution of this ENSO event. I have decided to use the prettied-up version that comes out on Mondays rather that the version that auto-updates daily because the SST Departures on the Equator do not change rapidly and the prettied-up version is so much easier to read. The bottom of the Hovmoeller which shows the current readings is now almost totally a mix of light blue and white. White is Neutral but the small amount of light Blue is where the temperature is in the marginal La Nina range. Remember the +5, -5 degree strip around the Equator that is being reported in this graphic. So it is the surface but not just the Equator. One now sees a bit more blue in the Nino 3.4 Measurement Area and a lot more further east. There is one warm spot at 160W.  So the Nino 3.4 Index is likely to be neutral this week. The curious brownish area between 150E and 160E is again pretty much gone this week. Week to week there have been no substantial changes. It was until recently ENSO Neutral with a warm bias. But since the end of July this has changed and you can see that in this Hovmoeller Graphic. The bottom sentence in the legend to the left of the graphic proper says it all.

This graphic is more focused on the Equator and looks down to 300 meters rather than just being the surface.

September 25, 2017 Upper Ocean Heat Anoma

The bottom of the Hovmoeller shows the current situation. If you look from the bottom of the graphic up you can see that any La Nina conditions (which NOAA declared to be a full La Nina event and we disagree) ended in December. At any rate the 2016 Cool Event is long gone. Successive Kevin waves early in 2017 which some thought might be initiating an El Nino in retrospect were not very impressive. We now see a blue (cool) area. It is now a bit more impressive with some dark blue.

Let us look in more detail at the Equatorial Water Temperatures.

We are now going to look at a three-dimensional view of the Equator and move from the surface view and an average of the subsurface heat content to a more detailed view from the surface down This graphic provides both a summary perspective and a history (small images on the right).

The NOAA graphic this morning was messed up and later was replaced by the graphic from last week and this is the graphic from a week ago.

.September 18, 2017 Kelvin Wave Analysis.

We are now starting to see the colder water make it far enough west to be in the Nino 3.4 Measurement Area. There is cool water at depth from 165W to 100W so we should expect lower Nino 3.4 readings in the weeks ahead. JAMSTEC it seems is paying attention to that yellow/orange area at about 150E which I gather they believe will this winter record as Neutral with a cool bias but not as cool as NOAA is forecasting.

Anomalies are strange. You can not really tell for sure if the blue area is colder or warmer than the water above or below. All you know is that it is cooler than usual for this time of the year. A later graphic will provide more information. Aside from buoyancy the currents tend to bring water from that depth up to the surface mostly farther east.

Now for a more detailed look. Below is the pair of graphics that I regularly provide. The date shown is the midpoint of a five-day period with that date as the center of the five-day period. The bottom graphic shows the absolute values, the upper graphic shows anomalies compared to what one might expect at this time of the year in the various areas both 130E to 90W Longitude and from the surface down to 450 meters. At different times and today in particular, I have discussed the difference between the actual values and the deviation of the actual values from what is defined as current climatology (which adjusts every ten years except along the Equator where it is adjusted every five years) and how both measures are useful for other purposes.

NOAA Website seems to be malfunctioning. The discussion after the graphics was prepared a few days ago and not update but most likely is still valid.

Subsurface Heat Anomalies

Re the top graphic, let us first look at surface temperature anomalies. Almost the entire surface of the Eastern Equatorial Pacific is cool. Subsurface Temperature Anomalies: There is a lot of cool water between 170W and 150W and it is in some places extending now to 200 meters. Further east it is not that deep. It now looks like enough cool water to sustain a La Nina. The bottom half of the graphic (Absolute Values which highlights the Thermocline) is now very useful. The 28C Isotherm is now located further west at about 170W. This graphic does not show a 27.5C anomaly which might more precisely indicate where convection is likely to occur. The 27C isotherm is now just west of 160W. The 25C Isotherm reaches the surface at 140W. What we have is La Nina conditions. The flattening of the Isotherm Pattern is an indication of ENSO Neutral just as the steepening of the pattern indicates La Nina or El Nino depending on where the slope shows the warm or cool pool to be. That flattening has occurred and we have gone to a Weak La Nina thermocline.

Here are the above graphics as a time sequence animation. You may have to click on them to get the animation going.

Equatorial Temperature Simulation

Isotherm Simulation

And now Let us look at the Atmosphere.

Low-Level Wind Anomalies near the Equator

Here are the low-level wind anomalies.

Low Level Wlind Anomalies

We now see easterly anomalies in the Nino 3.4 Measurement Area which means that the cool water below the surface will be rising to the surface as the water on the surface is blown to the west.

And now the Outgoing Long-wave Radiation (OLR) Anomalies which tells us where convection has been taking place.

OLR Anomalies Along the Equator

The pattern has changed. We no longer see suppressed Outgoing Long Wave Radiation (OLR) at the Dateline (no longer dry) but we again see enhanced OLR at 120E ( wet)

And Now the Air Pressure which Shows up Mostly in an Index called the SOI.

This index provides an easy way to assess the location of and the relative strength of the Convection (Low Pressure) and the Subsidence (High Pressure) near the Equator. Experience shows that the extent to which the Atmospheric Air Pressure at Tahiti exceeds the Atmospheric Pressure at Darwin Australia when normalized is substantially correlated with the Precipitation Pattern of the entire World. At this point there seems to be no need to show the daily preliminary values of the SOI but we can work with the 30 day and 90 day values.

Current SOI Readings

The 30 Day Average on September 25 was reported as 4.00 which is an ENSO Neutral value with a La Nina cool bias. The 90 Day Average was reported at 4.64 which is an ENSO Neutral value but creeping up there but not rapidly. The change from last week is insignificant. Looking at both the 30 and 90 day averages is useful and right now both are in agreement. They seem to be tracking the Nino 3.4 Index pretty well and reflect the downturn in marginal El Nino Conditions and short-term conditions in the Western Pacific where there there had been a long string of negative values for a while. Now the 30 day average is actually positive i.e. in the direction of a La Nina but still in the Neutral Range.

 

SOI = 10 X [ Pdiff - Pdiffav ]/ SD(Pdiff) where Pdiff = (average Tahiti MSLP for the month) - (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question. So really it is comparing the extent to which Tahiti is more cloudy than Darwin, Australia. During El Nino we expect Darwin Australia to have lower air pressure and more convection than Tahiti (Negative SOI especially lower than -7 correlates with El Nino Conditions). During La Nina we expect the Warm Pool to be further east resulting in Positive SOI values greater than +7).

To some extent it is the change in the SOI that is of most importance. The MJO or Madden Julian Oscillation is an important factor in regulating the SOI and Ocean Equatorial Kelvin Waves and other tropical weather characteristics. More information on the MJO can be found here. Here is another good resource.

Forecasting the Evolution of ENSO

Here is the primary NOAA model for forecasting the ENSO Cycle.

CFSv2 spread and bias correct ENSO forecast

This model is forecasting a La Nina. It probably is the most aggressive model re being so definitive about the ENSO Phase for this Fall and Winter.

Click here to see a month by month version of the same model but without some of the correction methodologies applied. It gives us a better picture of the further out months as we are looking at monthly estimates versus three-month averages.

From Tropical Tidbits.com

CDAS Legacy System

The above is from a legacy "frozen" NOAA system meaning the software is maintained but not updated. Notice since mid-July the collapse of Nino 3.4 values from the range of 0.5C to 0.6C down to Zero C and then down to -0.6C but recently moved back closer to 0C. .

The CFS.v2 is not the only forecast tool used by NOAA. The CPC/IRI Analysis which is produced out of The International Research Institute (IRI) for Climate and Society at Columbia University is also very important to NOAA. Below is the September 19 and September 14 CPC/IRI ENSO Forecasts

CPC/IRI September 19, 2017 ENSO Forecast

As you can see there has been some recent change to limit the period where La Nina is favored to just the Fall and Winter. The CFS.v2 model holds the La Nina conditions for perhaps an additional two months.

Forecasts from Other Meteorological Agencies.

Here is the Nino 3.4 report from the Australian BOM (it updates every two weeks)

Australia POAMA ENSO model run

Discussion Issued September 26, 2017

Tropical Pacific Ocean cooling expected to continue

The El Niño–Southern Oscillation (ENSO) is neutral. However, sea surface temperatures (SSTs) have cooled in the central to eastern tropical Pacific since mid-winter. These SSTs are currently cooler than average but within the neutral range. Waters beneath the surface are also slightly cooler than average. Other indicators of ENSO, such as the Southern Oscillation Index (SOI) and trade winds, also remain at neutral levels.

All international climate models surveyed by the Bureau suggest further cooling of the tropical Pacific Ocean is likely. Five of the eight models suggest SSTs will cool to La Niña thresholds by December 2017, but only four maintain these values for long enough to be classified as a La Niña event.

While unusual, it is not unheard of to see La Niña develop this late in the year—the Bureau will keep a close watch for further, or sustained, cooling of the equatorial Pacific. Of the late-developing La Niña events, their effect on summer rainfall has been mixed, with some leading to widespread wet conditions across eastern Australia, and others having minimal effect.

Here is the JAMSTEC forecast

September 1, 2017 JAMSTEC Forecast

It is not fully consistent with the NOAA forecast but much closer than the August 1 forecast..

Here is the discussion from JAMSTEC:

Sep. 19, 2017 Prediction from 1st Sep., 2017

ENSO forecast:

A weak La Niña-like pattern will persist until boreal spring of next year. Then, the tropical Pacific will return to a normal state by summer.

Indian Ocean forecast:

A positive Indian Ocean Dipole continues to exist as we have predicted but it will disappear by winter. In accord to the positive IOD, sea level anomalies continue to be negative (positive) in the eastern (western) tropical Indian Ocean. The tropical Indian Ocean will return to a normal state by winter.

Regional forecast:

On a seasonal scale, most part of the globe will experience a warmer-than-normal condition, while some parts of western Canada and western U.S. will experience a colder-than-normal condition in boreal fall. In winter, most parts of northern Europe, Russia, northern Canada, southern U.S., Mexico, southern Africa, Southeast Asia, China, and the Far East will experience a warmer-than-normal condition, while some parts of southern Europe, northern Africa, southern Canada, northern U.S., northern Brazil, and Australia will experience a colder-than-normal condition.

As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for some parts of East Africa, India, Philippine, and southern Mexico during boreal fall, whereas most parts of Indonesia, Australia, West Africa, southern Europe, eastern China, western U.S, and western Brazil will experience a drier condition during boreal fall. Those are partly due to the positive Indian Ocean Dipole. In winter, most parts of eastern U.S., Brazil, East Africa, and Australia will experience a wetter-than-normal condition, while some parts of western U.S., Peru, Indonesia, and the northeastern part of South Africa (around Limpopo Province) will experience a drier-than-normal condition.

Most parts of Japan will experience warmer- and wetter-than-normal conditions in fall. However, in late fall and winter, most parts of Japan will experience warmer- and drier-than-normal conditions.

Indian Ocean IOD (It updates every two weeks)

The IOD Forecast is indirectly related to ENSO but in a complex way.

IOD POAMA Model Run

Discussion Issued September 26

The Indian Ocean Dipole (IOD) is neutral and the model consensus suggests it will remain so. The weekly index value to 24 September was +0.02 °C. Three of the six climate models surveyed suggest positive IOD thresholds may be reached during spring, but it may now be too late to become an event. If a positive IOD eventuated it would be short-lived, as events typically decay by December. . A positive IOD is typically associated with below average spring rainfall over southern and central Australia.

IOD events typically decay during spring, and the influence of the IOD on Australian climate is weak during the months December to April. This is because the monsoon trough shifts south over the tropical Indian Ocean changing wind patterns, which prevents the IOD pattern from being able to form.

It is important to understand how and where the IOD is measured.

IOD Measurement Regions

IOD Positive is the West Area being warmer than the East Area (with of course many adjustments/normalizations). IOD Negative is the East Area being warmer than the West Area. Notice that the Latitudinal extent of the western box is greater than that of the eastern box. This type of index is based on observing how these patterns impact weather and represent the best efforts of meteorological agencies to figure these things out. Global Warming may change the formulas probably slightly over time but it is costly and difficult to redo this sort of work because of long weather cycles.

D. Putting it all Together.

At this time it would seem a La Nina is likely for this Fall and Winter. But the situation for next spring is not yet clear.

Forecasting Beyond Five Years.

So in terms of long-term forecasting, none of this is very difficult to figure out actually if you are looking at say a five-year or longer forecast.

The research on Ocean Cycles is fairly conclusive and widely available to those who seek it out. I have provided a lot of information on this in prior weeks and all of that information is preserved in Part II of my report in the Section on Low Frequency Cycles 3. Low Frequency Cycles such as PDO, AMO, IOBD, EATS. It includes decade by decade predictions through 2050. Predicting a particular year is far harder.

The odds of a climate shift for the Pacific taking place has significantly increased. It may be in progress. The AMO is pretty much neutral at this point (but more positive i.e. warm than I had expected) so it may need to become a bit more negative for the "McCabe A" pattern to become established. That seems to be slow to happen so I am thinking we need at least a couple more years for that to happen. So our assessment is that the standard time for Climate Shifts in the Pacific are likely to prevail and it most likely will be a gradual process with a speed up in less than five years but more than two years.

E. Relevant Recent Articles and Reports

Weather in the News

The latest GEI Maria Update

There are a lot of reports on damage assessment for Hurricanes Irma, Jose, and and Maria. We will do a comprehensive analysis at some point. The impacts are still occurring so it is too early to do the assessment.

Weather Research in the News

Nothing to Report

Global Warming in the News

Nothing to Report

F. Table of Contents for Page II of this Report Which Provides a lot of Background Information on Weather and Climate Science

The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page II where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.

1. Very High Frequency (short-term) Cycles PNA, AO,NAO (but the AO and NAO may also have a low frequency component.)

2. Medium Frequency Cycles such as ENSO and IOD

3. Low Frequency Cycles such as PDO, AMO, IOBD, EATS.

4. Computer Models and Methodologies

5. Reserved for a Future Topic (Possibly Predictable Economic Impacts)

G. Table of Contents of Contents for Page III of this Report - Global Warming Which Some Call Climate Change.

The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page III where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.

1. Introduction

2. Climate Impacts of Global Warming

3. Economic Impacts of Global Warming

4. Reports from Around the World on Impacts of Global Warming

H. Useful Background Information

The current conditions are measured by determining the deviation of actual sea surface temperatures from seasonal norms (adjusted for Global Warming) in certain parts of the Equatorial Pacific. The below diagram shows those areas where measurements are taken.

El Nino Zones

NOAA focuses on a combined area which is all of Region Nino 3 and part of Region Nino 4 and it is called Nino 3.4. They focus on that area as they believe it provides the best correlation with future weather for the U.S. primarily the Continental U.S. not including Alaska which is abbreviated as CONUS. The historical approach of measurement of the impact of the sea surface temperature pattern on the atmosphere is called the Southern Oscillation Index (SOI) which is the difference between the atmospheric pressure at Tahiti as compared to Darwin Australia. It was convenient to do this as weather stations already existed at those two locations and it is easier to have weather stations on land than at sea. It has proven to be quite a good measure. The best information on the SOI is produced by Queensland Australia and that information can be found here. SOI is based on Atmospheric pressure as a surrogate for Convection and Subsidence. Another approach made feasible by the use of satellites is to to measure precipitation over the areas of interest and this is called the El Nino - Southern Oscillation (ENSO) Precipitation Index (ESPI). We covered that in a weekly Weather and Climate Report which can be found here. Our conclusion was that ESPI did not differentiate well between La Nina and Neutral. And there is now a newer measure not regularly used called the Multivariate ENSO Index (MEI). More information on MEI can be found here. The jury is still out on MEI and it it is not widely used.

The below diagram shows the usual location of the Indo-Pacific Warm Pool. When the warm water shifts to the east we have an El Nino; to the west a La Nina.

Western Pacific Warm Pool

Click for Source

Interaction between the MJO and ENSO

This Table is a first attempt at trying to relate the MJO to ENSO

El Nino La Nina MJO Active Phase MJO Inactive Phase Relationship of MJO and ENSO Eastern Pacific Easterlies Western Pacific Westerlies MJO Active Phase MJO Inactive Phase

  • Weaker
  • Stronger
  • Part of Decay Process
  • Counteracts Easterlies
  • Enhances Easterlies
  • Stronger
  • May Create or Stimulate the Onset of El Nino via Kelvin Waves
  • Weaker
  • Part of Decay Process
  • Strengthens Westerlies
  • Weakens Westerlies
  • More likely
  • Stimulates
  • Less likely and weak
  • Retards development of a new La Nina
  • Stimulates the Jet Stream
 
  • Less Likely
  • Suppresses
  • More likely but weak
  • Accelerates development of a new La Nina and the Decline of a mature La Nina
 
  • Slows the Jet Stream and can induce a Split Stream especially during a La Nina

 

Table needs more work. Is intended to show the interactions. What is more difficult is determining cause and effect. This is a Work in Progress.

History of ENSO Events

With respect to relating analog dates to ENSO Events, the following table might be useful. In most cases this table will allow the reader to draw appropriate conclusions from NOAA supplied analogs. If the analogs are not associated with an El Nino or La Nina they probably are not as easily interpreted. Remember, an analog is indicating a similarity to a weather pattern in the past. So if the analogs are not associated with a prior El Nino or prior La Nina the computer models are not likely to generate a forecast that is consistent with an El Nino or a La Nina.

El NinosLa Ninas

  Start Finish Max ONI PDO AMO Start Finish Max ONI PDO AMO
            DJF 1950 J FM 1951 -1.4 - N
T JJA 1951 DJF 1952 0.9 - +          
  DJF 1953 DJF 1954 0.8 - + AMJ 1954 AMJ 1956 -1.6 - +
M MAM 1957 JJA 1958 1.7 + -          
M SON 1958 JFM 1959 0.6 + -          
M JJA 1963 JFM 1964 1.2 - - AMJ 1964 DJF 1965 -0.8 - -
M MJJ 1965 MAM 1966 1.8 - - NDJ 1967 MAM 1968 -0.8 - -
M OND 1968 MJJ 1969 1.0 - -          
T JAS 1969 DJF 1970 0.8 N - JJA 1970 DJF 1972 -1.3 - -
T AMJ 1972 FMA 1973 2.0 - - MJJ 1973 JJA 1974 -1.9 - -
            SON 1974 FMA 1976 -1.6 - -
T ASO 1976 JFM 1977 0.8 + -          
M ASO 1977 DJF 1978 0.8 N            
M SON 1979 JFM 1980 0.6 + -          
T MAM 1982 MJJ 1983 2.1 + - SON 1984 MJJ 1985 -1.1 + -
M ASO 1986 JFM 1988 1.6 + - AMJ 1988 AMJ 1989 -1.8 - -
M MJJ 1991 JJA 1992 1.6 + -          
M SON 1994 FMA 1995 1.0 - - JAS\ 1995 FMA 1996 -1.0 + +
T AMJ 1997 AMJ 1998 2.3 + + JJA 1998 FMA 2001 -1.6 - +
M MJJ 2002 JFM 2003 1.3 + N          
M JJA 2004 MAM 2005 0.7 + +          
T ASO 2006 DJF 2007 0.9 - + JAS 2007 MJJ 2008 -1.4 - +
M JJA 2009 MAM 2010 1.3 N + JJA 2010 MAM 2011 -1.3 + +
            JAS 2011 JFM 2012 -0.9 - +
T MAM 2015 AMJ 2016 2.3 + N JAS 2016 NDJ 2016 -0.8* + +

 

*The GEI Weather and Climate Report does not accept this as a legitimate La Nina. It is not unusual for different Meteorological Agencies to maintain different lists of El Ninos and La Ninas. This is usually because the criteria for classification differ slightly. Obviously the GEI Weather and Climate Report has no standing but nevertheless for any analysis we do, we will either not include or asterisk this La Nina to indicate that NOAA has it on their list and we consider that to be Fake News. The alternative is to conclude that the other Meteorological Agencies are not able to measuring things correctly. .

ONI Recent History

ONI History Updated on September 4, 2017

Another neutral reading. The MJJ reading was adjust downward from 0.3 to 0.2 a minor change. The full history of the ONI readings can be found here. The MEI index readings can be found here.

Four Quadrant Jet Streak Model Read more here This is very useful for guessing at weather as a trough passes through.

If the centripetal accelerations owing to flow curvature are small, then we can use the "straight" jet streak model. The schematic figure directly below shows a straight jet streak at the base of a trough in the height field. The core of maximum winds defining the jet streak is divided into four quadrants composed of the upstream (entrance) and downstream (exit) regions and the left and right quadrants, which are defined facing downwind.


Isotachs are shaded in blue for a westerly jet streak (single large arrow). Thick red lines denote geopotential height contours. Thick black vectors represent cross-stream (transverse) ageostrophic winds with magnitudes given by arrow length. Vertical cross sections transverse to the flow in the entrance and exit regions of the jet (J) are shown in the bottom panels along A-A' and B-B', respectively. Convergence and divergence at the jet level are denoted by "CON" and "DIV". "COLD" and "WARM" refer to the air masses defined by the green isentropes.

[Editor's Note: There are many undefined words in the above so here are some brief definitions. Isotachs are lines of equal wind speed. Convergence is when there is an inflow of air which tends to force the air higher with cooling and cloud formation. Divergence is when there is an outflow of air which tends to result in air sinking which causes drying and warming, Confluence is when two streams of air come together. Diffluence is when part of a stream of air splits off.]

Re Understanding the Southwest Monsoon this may may come in handy

Sierra Madre Mexico

Click here for a list of Sig Silber's Weather Posts

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