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posted on 04 December 2017

December 4, 2017 Weather and Climate Report - Active MJO to Arrive Soon

Written by Sig Silber

The Active Phase of the MJO should be impacting CONUS weather soon. Global Warming will be a tough sell in Ohio but not in Los Angeles. The warm Great Lakes are primed to produce Lake Effect Snow. NOAA is very confident in their Day 6 - 14 Forecast but just how hard is it to forecast it will AGAIN be dry almost all over and warm west/cold east. We begin our Count Down for the La Nina Demise this week. Read on for more details and maps. 


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Some housekeeping: On Saturday November 18, 2018 we published our monthly Seasonal Outlook Update and you can access that here. Also on Friday December 2 we published the December Update and you can access it here. Remember if you leave this page to go to links or if you have clicked to enlarge a graphic, in order to get back you need to hit the return arrow usually located on the left of your URL box on the upper left of the screen. If you have additional suggestions for improvement, please make them in the comments section following the article.

Post Mortem:

Here is what we  said in our lede paragraph last Monday:
A Pacific Trough is supposed to change the pattern, at least temporarily, in about a week. Is it real or hoped for?  We will try to sort that out in our Report tonight. The possibilities range from "no way" to "absolutely" or perhaps it will be "sort of" a change in pattern. There are in the forecast many moving parts to the equation that will impact the actual result.
Here is what happened. It is going to get colder. Snow mostly in the northern Rockies. Not a long lasting major pattern changer.
Why The moving parts did not coordinate and interact as forecast and some blocked each other. Moral of the story is that complex forecasts beyond 72 hours are risky. It works in the other direction also. That which is not expected to combine to produce extreme weather sometimes does.

 

La Nina Demise Count Down

Equatorial (0 - 300) meter heat content As reported December 4, 2017

Based on the above graphic we are starting our La Nina Demise Count-Down this week. The Upper-Ocean Heat Anomaly appears to be in decline. It is the reserves for maintaining a cool surface and when those cool reserves are depleted we return to ENSO Neutral.

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

I am starting with a summary first for temperature and then for precipitation of small images of the three short-term maps. You can click on these maps to see larger versions. The easiest way to return to this report is by using the "Back Arrow" usually found top left corner of your screen to the left of the URL Box. Larger maps are available later in the article with the discussion and analysis.

For most people, the summary with the small images will be sufficient. Later in the article for those with sufficient interest there is a full description of the factors determining the maps shown here with a detailed analysis of the ENSO situation which so dramatically impacts the forecasts below.

First Temperature

6 - 10 Day Forecast Temperature

Transitioning from the 6 to 10 day outlook on the left to the 8 to 14 day outlook on the right         →

8 - 14 Day Temperature

Slow zonal shift to the east. Brrr!

To the right is the week 3 and 4 Forecast.

There are now two warm anomalies and a Northeast cool  anomaly. →

3 - 4 Week Temperature

                     ↑

←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left seems feasible.
 

 

And then Precipitation

6 - 10 Day Forecast Precipitation

Transitioning from the 6 to 10 day outlook on the left to the 8 to 14 day outlook on the right.         →

8 - 14 Day Precipitation

Slow zonal shift to the east.

To the right is the week 3 and 4 Experimental Forecast.          →

Notice the large dry anomaly with the small wet anomaly tucked in. The dry anomaly looking ahead to weeks 3 and 4 is even larger than the prior forecast for what is now weeks 2 and 3 and is expanded to include the Northeast.

3 - 4 Week Precipitation

                      ↑

←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left seems feasible.

 

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

You can see moisture streaming into CONUS south of California and you can also see further north, moisture approaching CONUS but mostly north of CONUS. Remember this is an animation of what has happened not a forecast. 

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 December 4, 2017, as I am looking at the above graphic, you see mostly activity over the Great Lakes.

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. You can convert this graphic into a flexible forecasting tool by clicking here. One can obtain views of different geographical areas by clicking here.

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

There is no sign of major atmospheric rivers impacting CONUS.

Day One CONUS Forecast

Day Two CONUS Forecast

Day 1 Forecast Map

Day 2 Forecast

There is an area of snow which is all that developed except for a cold front from that much advertised Pacific Trough. Further east there is an area of instability which may have thunderstorm activity.

These graphics update and can be clicked on to enlarge but my brief comments are only applicable to what I see on Monday night  prior to publishing.

 

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. 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.

current highs and lows

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

What is Behind the Forecasts? Let us try to understand what NOAA is looking at when they issue these forecasts.

Below is a graphic which highlights the forecasted surface Highs and the Lows re air pressure on Day 7. The Day 3 forecast can be found here. the Day 6 Forecast can be found here. Actually all the small graphics below can be clicked on to enlarge them.

Day 7 Highs and Lows

When I look at this Day 7 forecast, there is a Low south of the Aleutians but further west than usual with surface central pressure of 984 hPa.  Further to the west there is a weak Low just west of Kamchatka with surface central pressure of 1004 hPa. There is over the Rocky Mountains a very strong High with surface central pressure of 1032 hPa. Thus any significant precipitation would be directed north of CONUS. The circulation of the Rocky Mountain High does invite cool air in from Canada on the eastern edge of that High.

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.

The table below showing the Day 3, Day 4, Day 5, Day 6 and Day 7 of this graphic can be useful in thinking about how the pattern of Highs and Lows is expect to move during the week.

Day 3 Day 4
Day 5 Day 6

From left to right and then down, Days 3 and 4 top row, Days 5 and 6 second row and Day 7 to the right. These are small images but you can if you want click on them and get larger images but even with the small images you can trace the evolution of the pattern. The graphics update but my commentary below does not so it is just a guide for how to read these graphics.

Day 7

We see a fairly stable situation for that five day period. The Pacific Low is dominating with the Hawaiian High visiting the Rocky Mountains.      

Things to look for are the position and strength of the Aleutian Low, the Hawaiian High and any troughs especially if they extend far to the south and are over water.

 

Looking at the current activity of the Jet Stream.  The below graphics and the above graphics are very related.

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.  I have not provided the ability to click to get larger images as I believe the smaller  images shown are easy to read.

Current Day 5
Current Jet Stream Jet Stream Five Days Out
You can sort of see a Pacific Trough in the "Current" graphic but on Day 5 it looks deeper actually south of CONUS. A key seems to be that it is mostly inland and not bringing in a lot of Pacific Moisture. But on Day 5 we also see the Jet Stream diving south in the Center of CONUS Brrr!

 

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.

500 MB Mid-Atmosphere View

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 generally signifies equal chances for snow at sea level locations. Thickness of 600 or more suggests very intensely heat and fire danger. Sometimes Meteorologists work with the 500 mb heights which provide somewhat similar readings to the "Thickness" lines but IMO provide slightly less specific information. Thinking about clockwise movements around High Pressure Systems and counter- clockwise movements around Low Pressure Systems provides a lot of information.

7 Day 500 MB Geopotential Forecast

What we see for Day 7 is the Western Ridge and blocking High and a major Eastern Trough. That is a very tight gradient of thickness levels. I think that means windy.

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

Seven Day WPC Quantitative precipitation forecast

We see mostly Eastern CONUS precipitation and not that much of it.

Four- Week Outlook: Looking Beyond Days 1 to 5, What is the Forecast for the Following Three + Weeks?

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

6 - 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on December 4, 2017 was 4 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 December 4, 2017 was 5 out of 5).

8-14 Day Temperature Outlook

Looking further out.

Experimental Week 3-4 Temperature Outlook

Now - Precipitation

6 - 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on December 4 was 4 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 December 4, 2017 was 5 out of 5)

Current 8 - 14 Day Precipitation Outlook

Looking further out.

Weeks 3 and 4 Experimental Forecast..

Here is the 6 - 14 Day NOAA discussion released today December 4, 2017 and the Week 3/4 discussion released Friday December 1, 2017

6-10 DAY OUTLOOK FOR DEC 10 - 14 2017

TODAY'S ENSEMBLE MEAN SOLUTIONS ARE IN GOOD AGREEMENT ON THE EXPECTED BROAD SCALE 500-HPA CIRCULATION PATTERN IN 6-10 DAY PERIOD. A HIGH AMPLITUDE TROUGH IS PREDICTED OVER THE ALEUTIANS, EXTENDING TO THE NORTHERN PACIFIC. DOWNSTREAM A STRONG RIDGE IS LIKELY TO BUILD ALONG THE WEST COAST WITH AN AMPLIFYING TROUGH OVER EAST-CENTRAL NORTH AMERICA. ABOVE NORMAL 500-HPA HEIGHTS ARE PREDICTED OVER ALASKA AND THE WESTERN CONUS. BELOW NORMAL 500-HPA HEIGHTS ARE FORECAST FOR THE CENTRAL AND EASTERN CONUS.  

BELOW NORMAL TEMPERATURES ARE LIKELY FOR THE MISSISSIPPI VALLEY AND SOUTHEAST TEXAS, AND THE EASTERN CONUS, UNDERNEATH THE PREDICTED DEEP TROUGH.  ABOVE  NORMAL HEIGHTS FORECAST OVER THE WESTERN CONUS AND SOUTHEASTERLY SURFACE FLOW OVER THE SOUTHWEST CONUS LEAD TO INCREASED CHANCES OF ABOVE NORMAL TEMPERATURES THERE. THE PREDICTED ANOMALOUS TROUGH OVER THE SOUTHERN ALEUTIANS AND THE NORTH PACIFIC ENHANCES CHANCES OF ABOVE NORMAL TEMPERATURES FOR ALASKA SOUTHERLY FLOW IS LIKELY IN THE LOWER LEVELS OVER MUCH OF THE STATE.  

EAST OF THE UPPER-LEVEL TROUGH PREDICTED OVER THE ALEUTIANS, SOUTHWESTERLY FLOW AT THE SURFACE INCREASES CHANCES OF ABOVE NORMAL PRECIPITATION OVER ALASKA AND THE ALASKA PANHANDLE. ABOVE NORMAL PRECIPITATION IS FAVORED FOR THE UPPER MISSISSIPPI VALLEY, THE WESTERN GREAT LAKES, AND NORTHERN PARTS OF THE NORTHEAST, DUE TO FRONTAL ACTIVITY. BELOW NORMAL PRECIPITATION IS LIKELY FOR MOST OF THE CONUS, WITH HIGH PROBABILITIES OF BELOW NORMAL PRECIPITATION ACROSS NORTHERN CALIFORNIA, THE PACIFIC NORTHWEST, THE MIDDLE AND LOWER MISSISSIPPI VALLEYS, SUPPORTED BY THE STRONG ANOMALOUS RIDGE FORECAST ALONG THE WEST COAST AND THE NORTHWESTERLY SURFACE FLOW OVER THE SOUTHEASTERN CONUS. THAT PATTERN IS CONSISTENT WITH ESTIMATES FROM THE ECMWF AND GEFS REFORECAST TOOLS.  

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE PREDICTION TOOLS, OFFSET BY MODERATE SPREAD AMONG THE COMPONENT ENSEMBLE MEMBERS.

8-14 DAY OUTLOOK FOR DEC 12 - 18 2017 

THE 500-HPA PATTERN DURING THE 8-14 DAY PERIOD IS PREDICTED TO BE SIMILAR TO THAT OF THE 6-10 DAY PERIOD. THE PATTERN IS PREDICTED TO BE HIGHLY AMPLIFIED  OVER THE NORTH AMERICAN SECTOR. ANOMALOUS RIDGING ALONG THE WEST COAST AND TROUGHING CENTERED OVER THE OHIO VALLEY IS PREDICTED TO CONTINUE. MODEL AGREEMENT ON THAT OVERALL PATTERN IS QUITE HIGH WITH ONLY MINOR DIFFERENCES OVER NORTHERN MEXICO IN THE IDEA OF SOME TROUGHING UNDERCUTTING THE RIDGE OUT WEST. INTRAMODEL SPREAD, ASSESSED VIA THE SPAGHETTI PLOTS, IS LOW OVER THE EASTERN CONUS. THE ONLY AREAS OF SUBSTANTIAL UNCERTAINTY ARE OVER NORTHERN ALASKA DUE TO DIFFERING AMPLITUDE OF THE RIDGE, AND OVER THE SOUTHWEST,  ASSOCIATED WITH POTENTIAL UNDERCUTTING OF THE WESTERN RIDGE.

THE TROUGHING OVER THE EASTERN CONUS IS EXPECTED TO SUPPORT ANOMALOUSLY COLD AIR FROM THE GREAT PLAINS TO THE EAST COAST; WHILE ABOVE NORMAL TEMPERATURES ARE FAVORED FROM THE GREAT PLAINS TO THE WEST COAST, AND OVER ALASKA. THE HIGHEST ODDS FOR BELOW NORMAL TEMPERATURES ARE OVER THE OHIO VALLEY, CENTRAL APPALACHIANS AND LOWER GREAT LAKES REGION. 

STRONG RIDGING OVER THE WESTERN CONUS FAVORS BELOW NORMAL PRECIPITATION FOR THE  PACIFIC NORTHWEST, GREAT BASIN, AND SOUTHWEST. THE RIDGING IS ALSO LIKELY TO STEER STORMS INTO SOUTHERN ALASKA. TROUGHING OVER SOUTHEAST CANADA IMPLIES  STORM ACTIVITY FROM THE NORTHERN PLAINS TO THE NORTHEAST, WHERE NEAR TO ABOVE NORMAL PRECIPITATION IS FAVORED, ESPECIALLY DOWN WIND OF THE GREAT LAKES. BELOW NORMAL PRECIPITATION IS FAVORED FOR THE SOUTHERN GREAT PLAINS, AS ANY FRONTS THAT MOVE ACROSS THE REGION ARE LIKELY TO BE MOISTURE STARVED, THOUGH THOSE SAME FRONT MAY SETTLED ACROSS FLORIDA, SO UNCERTAINTY IN THE PRECIPITATION  OUTLOOK IS HIGHER OVER FLORIDA THAN OTHER PLACES IN THE SOUTHEAST.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS: MUCH ABOVE AVERAGE, 5 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE ENSEMBLE MEANS AND LOW SPREAD EVEN AMONG THE ENSEMBLE MEMBERS.

Week 3-4 Forecast Discussion Valid Sat Dec 16 2017-Fri Dec 29 2017

The Week 3-4 outlook this week continues a transition that began last week. A large pattern change is forecast during the Days 5-7 period, and the various dynamical models keep the forecast pattern intact through Week-2 and into the Weeks 3-4 period. The background state remains grounded in the ongoing La Nina, and a robust MJO event is forecast to propagate from the Maritime Continent to the West Pacific over the next one to two weeks.

The Week-2 forecast circulation pattern depicts above-normal 500-hPa heights over much of the northern latitudes, with a negative AO index forecast through Week-2. The forecast pattern change that was targeted for late Week-2 and Week-3 last week is still on target, with the current Week-2 forecast showing negative height anomalies centered near the Great Lakes. All three of the operational ensemble systems agree on the large-scale circulation persisting into Weeks 3-4, with some eastward progression. A blend of the CFS, ECMWF, and JMA ensemble mean 500-hPa height fields shows a coherent wave pattern with above-normal heights centered west of Hawaii, anomalous troughing centered just south of the Aleutians, and above-normal heights centered generally over the North Pole. Negative height anomalies are forecast from east-central North America eastward to far northwestern Europe.

The MJO has recently amplified over the eastern Indian Ocean and Maritime Continent. The ECMWF and GEFS each forecast eastward propagation across the to the West Pacific by the end of Week-2. A wet West Pacific and dry Indian Ocean convective dipole favors the development of a mid-latitude and polar circulation response similar to the forecast pattern depicted in the various ensemble mean solutions. Given the forecast MJO evolution, the MJO extratropical response is likely to be most pronounced during Week-4 and beyond.

The forecast temperature pattern for Weeks 3-4 incorporates the objective blend of the CFS, ECMWF, and JMA model forecasts, as well as statistical guidance primarily from the multiple regression tool that leverages trends along with current ENSO and MJO conditions. The main difference between the objective blend and the official forecast is that probabilities favoring above-normal temperatures over the northern Rockies and northern Plains have been reduced or eliminated. This is based on the statistical guidance; over this region the low-frequency state and forecast MJO evolution would be constructively interfering in a way that would progressively favor below-normal temperatures. Given the above-normal temperatures forecast by the numerical guidance, uncertainty is especially high for the north-central CONUS. The various forecast guidance was in very good agreement over Alaska, where there is a greater than 70 percent chance of above-normal temperatures for some parts of the state.

The precipitation outlook is likewise based on the objective dynamical guidance, which is broadly consistent with the forecast circulation pattern and, to lesser extent, the low-frequency La Nina footprint. Below-normal precipitation is most likely for the central U.S. where anomalous northerly mid-level flow is forecast. This area extends through the Southwest and up the West Coast downstream of the forecast upper-level ridge. There is a slight tilt toward above-normal precipitation centered over the Northern Rockies, where upslope precipitation may become more frequent as surface high pressure noses southward over the High Plains. There remains a great deal of uncertainty over the eastern U.S. where the ultimate position of the mean frontal zone will likely determine precipitation anomalies over the forecast period. Anomalous mid-level flow over southern and southwestern Alaska favors above-normal precipitation south of the Alaska Range, while precipitation deficits are more likely over parts of interior Alaska.

The temperature forecast for Hawaii remains a bit uncertain with the CFS and ECMWF depicting oppositely signed anomalies during the period. Given the slightly above above-normal SSTs in the region, there is a slight tilt toward above-normal temperatures. The various guidance is in good agreement favoring increased odds of below-normal precipitation over Hawaii, a fairly big change from last week. This appears to be consistent with above-normal 500-hPa heights forecast near and west of Hawaii during this period.

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

Nov 15, 1953 Neutral - +  
Nov 13, 1960 Neutral N +  
Nov 14, 1962 Neutral - +  
Nov 23, 1966 Neutral - +  
Nov 23, 1969 El Nino + - Modoki
Nov 13, 1971 La Nina - -  
Dec 16, 1986 (twice) El Nino + - Modoki
Nov 17,  2004 El Nino - + Modoki Type II
Nov 20, 2004 El Nino - + Modoki Type II

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

The spread among the analogs from November 12 to December 16 is 34 days which is just a bit longer 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 November 30 although the two December 16 analogs skew the results a bit. These analogs are centered on 3 days and 4 days ago (December 1 or December 2). So the analogs could be considered to be pretty much in sync with respect to weather that we would normally be getting right now with perhaps a slight bias of being a bit late. For more information on Analogs see discussion in the GEI Weather Page Glossary.

Including the duplicates, there are four Neutral Analogs, just one La Nina analog and five El Nino Analogs. The phases of the analogs are most consistent with McCabe A and D. These are opposites and I am not sure what to make of that.

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.

In color Black and White same graphics
McCabe Maps modified to include the subtitles 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.

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.

And the 30 Days ending November 25, 2017 And the 30 Days ending December 2, 2017

November 25, 2017 30 Day Temperature and Precipitation Departures

December 2, 2017 30 Day Temperature and Precipitation Departures
Not a lot of change. It is a bit drier. The temperature anomalies are a bit more pronounced but more or less in the same location. It keeps on getting drier. The Northern Cool Anomaly has washed out but the Southwest Warm Anomaly is thriving.
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

 

Looking Out Beyond Three Months

On Saturday November 18, 2018 we published our monthly Seasonal Outlook Update and you can access that here. Also on Friday December 2 we published the December Update and you can access it here. There will be a new Seasonal Outlook issued by NOAA on December 21 which we will report on December 23.

Reference Forecasts Full Month and Three Months.

Below are the Temperature followed by the Precipitation Outlooks for the month and three months shown in the Legend. These map are issued on the Third Thursday of the Month. The maps for the following month (but not the three-month maps) are 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. Also the three shorter-term maps will generally cover a slightly different time period since they update daily as the month progresses. But these reference maps are sometimes useful if one wants to understand how the current month was originally forecast to play out.

 
December Temperature Outlook Update on November 16, 2017 To the left is the full month Temperature Outlook. To the right is the three-month Temperature outlook DJF Temperature  Issued on November 16,2017
December 2017 Precipitation Outlook Updated on December, 2017 To the left is the full month Precipitation outlook. To the right is the three-month Precipitation outlook. DJF 2017-2018 Precipitation Outlook Issued on November 16,  2017

 

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

It is Useful to Understand the Semipermanent Pattern that Control our Weather and Consider how These Change from Winter to Summer. These two graphics (click on each one to enlarge) are from a much larger set available from the Weather Channel.  They highlight the position of the Bermuda High which they are calling the Azores High in the January graphic 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 moving into December and are more than 5/6ths 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 Winter position of the Pacific High. Right now it is not in the January Position or close to it. But it may be for a short time in a week or so according to the forecast.

Same as above but for July

 

Forecast for Today (you can click on the maps to enlarge them)
 

This graphic is anomalies i.e. deviations from normal not the actual temperatures. This graphic is actuals not anomalies as is the case in the temperature map.
Temperature at 2 Meters Maine Reanalyer
Notice that below the map there is a tabulation of magnitude of the current anomalies by region. Overall it is warmer than climatology especially the Arctic. Actually there is really only one large cool anomaly shown and that is Eastern Siberia We again see the dry area from North Africa through Asia other than (a small part of) extreme Southeast Asia but including most of India. South America south of the ITCZ is mostly wet until you get south of Brazil. Africa north of the Equator and the ITCZ is mostly dry but the wet zone extends fairly far south. Australia is mostly dry. Extreme Southern Europe is wet.

 

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

Precipitation

BOM Current Temperature Wedensday

BOM World Preciptation  Wednesday

Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader. I do not see much of interest for the Northern Hemisphere

 

And now we have experimental forecasts from the U.S. NAEFS Model.

Temperature Precipitation

NAEFS 8 - 14 Day Temperature

NAEFS Experimental World Precipitation

Perhaps we see the impact of a negative Arctic Oscillation on Europe. You definitely see the La Nina pattern for North America.

 

Looking Out a Few Months

Here is the precipitation forecast from Queensland Australia:

Consistently positive SOI  forecast for January to Febrruary 2017.- 2018

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 continuance of the underlying driver of the SOI having been consistently positive. CONUS now looks like a north south typical La Nina divide with the northern tier wet. Northwest South America is wet. Southern Africa is wet. Eastern Australia is 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. If we want to have a good feel for future weather we need to look at the oceans as our weather mostly comes from oceans and we need to look at

  • Surface temperature anomalies (weather develops from the ocean surface  and
  • the changes in the temperature anomalies since that may provide clues as to how the surface anomalies will change based on the current trend of changes. This is not that easy to do since the oceans are deep, there are many currents, winds have an impact etc. Two ways that are available to use are to look at the change in the situation today compared ot the average over a period of time and NOAA also produces a graphic of monthly changes. I use both. The first set of graphics is simply looking at the average compared to today and that is below.
Three Month Average Anomaly Current Anomaly
Three month average anomaly Daily SST Anomaly
La Nina shows up La Nina is more intense

 

And when we look in more detail at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.

                              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
Fairly Neutral

Cool North of Japan and west of Kamchatka but warm east of Japan and Kamchatka.

Warm off Baja and further north cool out towards but north of Hawaii.

Warm off East Coast and Gulf of Mexico

Warm north of Scandinavia,

Warm south and west of Greenland. Fairly extreme in Labrador Sea

Equator

Pacific cool east of Dateline. Indicative if Inactive Phase of MJO 

SST Daily Anomalies
Africa West of Australia North, South and East of Australia

West of South America

East of South America

Warm west of North Africa.

Warm east of Tanzania

Cool off Namibia

Slightly cool offshore

Very warm southeast all the way to New Zealand.

Cool, cool, cool but slightly offshore of Ecuador and Peru.

Cool south of 40S and east of 30S but minor.

 

Then we look at the change in the anomalies.  Here it gets a little tricky as for this graphic red does not mean a warm anomaly but a warming of the anomaly which could mean more warm or less cool and blue does not mean cool but more cool or less warm.

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

Black Sea warming. Western Mediterranean cooling.

Arabian Sea cooling.

Cooling between China and Japan.

Cooling to the west of Kamchatka

Warming both sides of the Dateline at about 30N to 50N

Cooling Bristol Bay i.e. north of Aleutians.

Cooling east of the large warming area discussed in to the left of this table cell.

Warming west of CONUS and Baja.

.

.

Cooling off Nova Scotia

Warming Gulf of Mexico.

Cooling  Western Caribbean

Cooling Labrador Sea, south of Greenland and east of British Isles.  .

Equator Eastern Pacific mixed but more cooling than warming. Atlantic cooling near Africa. Cooling for Maritime Continent.
Change in weekly anomalies December 4, 2017
Africa West of Australia North, South and East of Australia West of South America East of South America

Warming west of Gulf of Guinea.

Cooling west of Namibia

Stable

Cooling to the north and east.

Warming to the south

Band of cooling 15S extending beyond  Dateline.

Cooling 20S to 50S

 

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   +0.12 +0.17 +0.0
April   +0.52 +0.29 +0.2
May   +0.30 +0.32 +0.2
June   +0.19 +0.31 0.0
July   -0.50 +0.31 0.0
August   -0.68 +0.31 +0.4
September   -0.28 +0.35 +0.2
October   -0.60 +0.44  0.0
November   NA NA Est 0.0

 

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 December 4 for what is shown as Week Two, the period December 6 to December 12, 2017, we see wet conditions* and cyclone development* for the eastern Maritime Continent and small areas of wet and dry for parts of Brazil and also wet conditions* for part of Western Africa (10S).

 * 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.

Tropical Activity Possibly Impacting CONUS.

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.

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 in order 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 very cold water to the south of the Equator with less cold water to the north of the Equator. That means a currently weak ENSO La Nina Phase.

The below table only looks at the Equator (and starting this week I am including large anomalies just off the Equator also) 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 by ENSO Phase

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)

NA

NA

0

0

0

+0.5C to +1C (marginal)

NA

NA

0

0

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

170E

175E

5

0

20

0C or cooler Anomaly (coolish neutral)

175E

150W

25

20

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

150W

145W

5

5

30

-1.0C or cooler Anomaly

145W

130W

102W

142W

120W

LAND

20

13

-1.5C or cooler Anomaly

142W

120W

130W

102W

30

12

-2.0C or cooler Anomaly

LAND

LAND

0

0

-2.5C or cooler Anomaly

LAND

LAND

0

0

There is more area in ENSO Neutral this week.

 

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 December 4, in the afternoon working from the December 3 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 Nino 3.4 from TAO/TRITON Graphic

Anomaly Segment Estimated Anomaly
  Last Week This Week
A. 170W to 160W -0.6 0.0
B. 160W to 150W -0.5 -0.1
C. 150W to 140W -1.0 -0.8
D. 140W to 130W -1.2 -1.1
E. 130W to 120W -1.2 -1.0
Total -4.5 -3.0
Total divided by five i.e. the Daily Nino 3.4 Index (-4.0)/5 = -0.8 (-3.0)/5 = -0.6

 

My estimate of the daily Nino 3.4 SST anomaly tonight is -0.6 which is a weak ENSO La Nina value. NOAA has reported the weekly Nino 3.4 to be -0.7 which is a weak La Nina value. Nino 4 is reported slightly warmer at 0.0. Nino 3 is the same at -1.1. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported slightly cooler at -1.3. 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. 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. The same data in table form but going back a couple of more years can be found here.

The cool anomaly pretty much  remained in the same locating this week and again records as La Nina.

December 4, 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.

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

Equatorial (0 - 300) meter heat content As reported December 4, 2017

The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2016. We may be at Peak La Nina but it has now only a few months to run and we are starting our La Nina Demise Count Down this week.

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.

December 4, 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 shows the current readings. 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.

Not much changed from last week. You can see where La Nina took a vacation but it was a short vacation.

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

December 4, 2017 Upper Ocean Heat Anoma

The bottom of the Hovmoeller shows the current situation.

The pattern this week is very similar to last week.

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).

.December 4, 2017 Kelvin Wave Analysis.

Winds or currents are keeping much of the cool water just below the surface. There is cool water at depth from the 160W to LAND. The cool water is reaching the surface mostly from 170W to 150W and again from145W to 130W so only part of the cool anomaly is reaching the surface in the Nino 3.4 Measurement Area. It is about the same this week than last week. We also see a growing warm water anomaly extending from the west to the Dateline and now beyond to 160W. It is at depth not on the surface but it is signaling the probable end of this La Nina not to an El Nino but to ENSO Neutral but it will take a while for that warm water to arrive in the Nino 3.4 Measurement Area. BUT IT MAY HAPPEN MORE RAPIDLY THAN THE MODELS ARE SHOWING.  We will start our La Nina demise count down next week.

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 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.

There is cold water from 170W to Land. At  the west end of the cool anomaly it is now not quite 200 meters deep. We now have warm water developing west of the Dateline and starting to cross the Dateline. It is now intruding into the Eastern Pacific Nino 3.4 Measurement Area but at depth not at the surface. La Nina's days are numbered but in terms of months not weeks or days.
Subsurface temperature Anomalies
The 28C Isotherm is at 175W, the 27C Isotherm is at 170W, the 25C Isotherm is at 145W.

 

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.

Tracking the change.

Sepember 15, 2017 Subsurface Water Temperatures Equatorial Ocean Subsurface as of November 29, 2017

 

I have "frozen" the graphic on the left side above which shows the situation as reported for September 15, 2017. The one on the right which is top half of the above graphic is updated by NOAA every five days but I have to update this snipped portion of that graphic into this article manually so the two can get out of phase by five days. It shows the situation now.  The situation is not much different east of the Dateline from the situation as reported for September 15, 2017. But west of the Dateline it looks a lot different  i.e. warmer. We use the graphic on the left as a reference to see how the current situation changes over time.

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.

The 850 hPa level is above the surface but close to the surface.

And now the Outgoing Long-wave Radiation (OLR) Anomalies which tells us where convection has been taking place. The bottom of a Hovmoeller graphic shows the most recent readings.
Low Level Wlind Anomalies

OLR Anomalies Along the Equator

Reds and browns would be suppressed easterlies or enhanced westerlies and are typical of El Nino. We have the opposite. We see suppressed Outgoing Long Wave Radiation (OLR) at the Dateline i.e (dry) and we  see enhanced OLR at 120E ( wet)

 

And Now the Air Pressure to Confirm that the Atmosphere is Reacting to the Sea Surface Temperature Pattern. The most Common way to do that is to use 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 December 4 was reported as 10.44 which is a La Nina value. The 90 Day Average was reported at 9.08 which is also a La Nina value. Looking at both the 30 and 90 day averages is useful and right now both are in agreement with the 90 day lagging the 30 day as one would expect. But the decline in the 90 Day average needs to be watched. We may be seeing some MJO impacts here.

 

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. The CDAS model is a legacy "frozen" NOAA system meaning the software is maintained but not updated. We find it convenient to obtain this graphic from Tropical Tidbits.com

CFSv2 spread and bias correct ENSO forecast

CDAS Legacy System

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. Notice that since mid-October, the Nino 3.4 Index has been in a declining channel. It is not in conflict with the primary NOAA model but shows daily values rather then smoothing them out like the CFSv2 Model does.

 

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 are the November 9 and November 20 CPC/IRI ENSO Forecasts

November 20, 2017 CPC/IRI ENSO 3.4 forecast.

when you look at this graph you see four blue bars in the earlier graph and only three in the mid-month graph but that is because the early graph has OND in it and the second graph does not. So it really is not a big change except for FMA which favored La Nina in the early survey based analysis and now favors ENSO Neutral which is not a surprise to us.

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

And the Discussion Issued on December 5, 2017:

La Niña established in tropical Pacific

The Bureau’s ENSO Outlook has been raised to LA NIÑA, indicating that the tropical Pacific has reached La Niña levels. International climate models surveyed by the Bureau indicate that further cooling of equatorial Pacific Ocean sea surface temperatures is expected over summer.  All of the eight models reach or surpass La Niña thresholds during December 2017. Seven of the eight models sustain the conditions long enough to be considered an event, where persistence for three months is generally the minimum length required. [Editor’s Note: the NOAA criteria are far longer but require a smaller Nino 3.4 anomaly for La Nina Conditions to be declared to have been a full La Nina]  Climate models suggest this La Niña will be weak and short-lived, persisting until early southern autumn 2018.

Signs of La Niña in the equatorial Pacific have increased during spring. The central to eastern tropical Pacific Ocean has cooled steadily since winter, and is now at La Niña thresholds (0.8 °C below average). Atmospheric indicators, including the Southern Oscillation Index (SOI), trade winds and cloud, also show clear La Niña patterns.

In order for 2017–18 to be classed as a La Niña year, the event needs to last for at least 3 months. Climate models surveyed by the Bureau suggest that while this event is likely to persist over the southern summer, it will be weaker than the strong La Niña of 2010–12.

La Niña typically brings above average rainfall to eastern Australia during late spring and summer. However, sea surface temperature patterns in the Indian Ocean and closer to Australia are not typical of a La Niña event, reducing the likelihood of widespread above average summer rainfall. La Niña can also increase the chance of prolonged warm spells for southeast Australia.

Here is the most recent JAMSTEC forecast issued on November 1, 2017

November 1, 2017 JAMSTEC Forecast

And here is the short discussion that was released on November 22, 2017

Nov. 22, 2017 Prediction from 1st Nov., 2017

ENSO forecast:

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

Indian Ocean forecast:

A normal state in the tropical Indian Ocean will persist until spring of next year. Then we expect a positive Indian Ocean Dipole in summer of 2018. However, there is a large uncertainty in the prediction at present because of the large spread in the prediction plumes of the dipole mode index.

Regional forecast:

On a seasonal scale, most part of the globe will experience a warmer-than-normal condition, while some parts of Africa and Brazil will experience a colder-than-normal condition in boreal winter.

As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for some parts of East Africa, eastern Southern Africa, Philippine, East Australia, and northern Brazil during boreal winter, whereas most parts of Indonesia, West Australia, West Africa, southern Europe, western U.S, eastern China and southern Brazil will experience a drier condition during boreal winter. Those are partly due to the weak La Niña-like condition.

In 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 December 5

Indian Ocean Dipole outlooks

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 3 December was +0.05 °C. All six of the climate models surveyed by the Bureau indicate that the IOD will remain neutral into early 2018.

The influence of the IOD on Australian climate is weak during 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.

However, to the south of the traditional Indian Ocean Dipole regions, cooler than average sea surface temperatures in the eastern Indian Ocean may be limiting the feed of moisture over Australia, and opposing more typical La Niña influences.

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 here for this Winter and Spring. But the situation for next Summer is not yet clear. However, we are getting very close to being able to forecast the end of this La Nina event. But it may only be a temporary end for the Summer and next Fall as it may return for next Winter or Spring.

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. The next El Nino may be the trigger.

E. Relevant Recent Articles and Reports

Weather in the News

Active Eastern Pacific Hurricane Season Ends

Brutal Atantic Hurricane Season

Weather Research in the News

Nothing to Report

Global Warming in the News

Satelling Bulk Tropospheric Temperatures as a Metric for Climate Sensitivities 

Indonesia's Volcano and Climate Change

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 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 as measured by the ONI

December 4, 2017 Revised Historical ONI Readins.

Note: Without fanfare the base climatology was recently changed from ERSST.V4 to ERSST.V5. This is done every five years and is totally proper but it does shuffle the deck re what were and were not ENSO events so it perhaps should have had more press but that is not the fault of NOAA but if they had kept me in the loop I would have covered it. I was not excluded just not included and did not notice it until after the fact. No big  deal but it is important. 

The new SON reading of -0.7 is the first La Nina Reading. These would have to extend through JFM 2018 for this to be recorded as a La Nina. The chances of this are about  50:50. 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.]

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

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