December 24, 2018 Intermediate-Term Weather Report – Blocking Patterns are Complicating Things

Written by Sig Silber

If you wonder why I have been talking a lot about the MJO it is because El Nino is not here yet so the major tropical influence is the MJO which has a 60 day cycle around the World along the Equator but can have somewhat similar but weaker impacts as the ENSO cycle. However they occur much faster than the ENSO Equatorial Cycle which is on average approximately one or two years “on” (El Nino) , three years “Neutral” and two years “off” (La Nina). Until and “IF” we actually get a real El Nino, other factors have more control over CONUS weather. That is to a large extent the case for the period of time covered by this report. 

Please share this article – Go to very top of page, right hand side for social media buttons.

Tonight, I focus on the next 25 days but also express some doubts about the assumption that we will have a real El Nino this winter. There are some factors which make the forecast this week a bit complicated especially in terms of pinning down the days when specific things will happen. That timing has an impact on potential severe events.

From the Atlanta NWS Sunday Evening:

Long term /Wednesday through Monday/… extended forecast looking increasingly wet, and have issued hydrologic outlook to frame the threat of flash flooding. Period of heaviest rainfall continues to be Thursday and Friday, but extended models continue to suggest that wet conditions will persist into next week. Atlanta is shaping up to have one of the wettest years on record (currently sitting at 65.18 inches, or 8th wettest year for Atlanta. Record is 71.45 inches in 1948. Current forecast package has around 4 inches for Atlanta through  new years eve.)

For the Atlanta area the best resource is the Atlanta NWS Office. For the broader area a good resource is our Severe Weather Event article which can be found here. Severe weather can develop quickly and there are both a couple of maps where such events will be shown and you can then click on them to get detailed information. At the bottom of the article there are some links can take you to watches and warnings if they have been issued. If you send this article to yourself it will be in your email. The latest version can be found at our weather directory which can be accessed here. But the older versions of that article are live and continue to update so NOAA information continues to be able to be accessed from older versions…only my commentary which is very limited in that article may become out of sync with what is going on.

What is going on is described in part by the NYC NWS.

Deep layered ridging over the eastern US Wed and Thu will provide dry and seasonable weather. Meanwhile, a deep trough near the Continental Divide Wed morning will slow as it tracks east then NE through the Central Plains due to downstream ridging  and a strengthening Canadian vortex near Hudson Bay blocking it’s eastward and forward progression. It will eventually merge with the Canadian vortex late in the week and race through the Great Lakes and southeast Canada Fri/Fri night.

I should not be covering this today but in Part II of the Seasonal Analysis when I write it but I could not resist.

 Now to our Current Weather starting with key highlights.

Here is the recent history of the overall pattern for North America and the North Pacific.

We now provide our usual summary first for temperature and then for precipitation of small images of the four 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.

Sometimes it is useful to see the evolution of the forecasts from the 1 – 5 Day, 6 – 10 Day (which NOAA considers to be Week-1 of their intermediate forecast) , 8 – 14 Day (which NOAA considers to be Week-2) and Week 3 and 4 (which after being issued overlap with Week-2). I do not have comparable maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing for temperature is the Day 3 Maximum Temperature and for precipitation the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week but showing absolute QPF (inches of precipitation) not QPF deviation from Normal.

First Temperature

This shows magnitude rather than probability of being higher or lower than Normal and shows the middle day of the five day period.	The pattern is now mostly zonal (west to east versus meridional north to south to north).  The cool anomaly will gradually deamplify. It is hardly moving re west to east zonal progression.		The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems questionable but is consistent with the monthly forecast shown below. So we may even be able to see the next warm anomaly to the far west of the 8 – 14 Day Forecast.

And then Precipitation

The five day QPF is shown above. The units are different than the other maps i.e. in units of precipitation (inches) not probabilities of exceeding or being less than climatology.	The Northwest dry anomaly looks to expand east. That could be a west to east movement or a north to south movement in from Canada that then looks like a west to east movement.		The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems feasible. It is certainly not a full El Nino Pattern. But it is more southerly oriented than the recent pattern.

Because some may have missed it here is a repeat of the new January and three-month forecasts.

	Temperature	Precipitation
January
Three Months

A. Now we will begin with our regular approach and focus on Alaska and CONUS (all U.S.. except Hawaii).

Water Vapor.

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

You can see from this animation that there has been moisture entering CONUS from the Pacific and also impacting CONUS further south as the Jet Stream has been split. But there is a break in the inflow into the Northwest.

Tonight, Monday December 24, 2018, as I am looking at the above graphic, you see the same pattern. And you can see that there will be a break in the storm flow into the Northwest

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.

The above is not updating (check the date in that graphic) and it is not directly related to the Partial Government Shutdown so we have added another graphic that focuses only on the West Coast.

And Now the Day One and Two CONUS Forecasts

Additional useful forecasts are available from our Severe Weather Report which this week can be found here and always can be located via this directory.

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.

The below makes it easier to focus on a particular day.  The best way to read them is from left to right on the first row and then from left to right in the row below it.

include(“/home4/aleta/public_html/pages/weather/modules/Weather_Map_by_Day_Matrix.htm”); ?>

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 forecast 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.

The Aleutian Low is quite strong with surface central pressure of 976 hPa and is centered over the Western Aleutians. The Hawaiian High is shown tonight a bit stronger than recently with surface central pressure of 1028 hPa. We see a High over the Central Rockies with surface central pressure of 1032 hPa in Canada but declining further south. South of Greenland there is a Low with central surface pressure of  992 hPa. It covers a large area including Hudson Bay. Over Kamchatka there is a High with surface central pressure of 1024 hPa. It is not a very complex situation but there are always complications.

include(“/home4/aleta/public_html/pages/weather/modules/Air_Pressure_Map_by_Day_Matrix.htm”); ?>

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
You can see the current pattern here.	There is a trough that moves south which will dominate first the West Coast weather and later the Southeast and perhaps the Northeast also.

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.

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

Here is the whole suite of similar maps for Days 3, 4, 5, 6 and repeated for Day 7. It is quite complicated. Read from left to right first  row and then left to right on the  second row. 

include (“/home4/aleta/public_html/pages/weather/modules/500_Millibar_by_Day_Matrix.htm”); ?>

We are showing both the situation on the surface and at mid-atmosphere 500 mb and the view is different so sometimes it is useful to simply be able to compare them.

Here is the seven-day cumulative precipitation forecast. More information in how to interpret this graphic is available here.

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 24, 2018 was 3 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on December 24, 2018 was 3 out of 5).

–

Looking further out.

Now – Precipitation

6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on December 24, 2018 was 3 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on December 24, 2018 was 3 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today December 24, 2018

6-10 DAY OUTLOOK FOR DEC 30, 2018 – JAN 03, 2019  

TODAY’S ENSEMBLE MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE PREDICTED 500-HPA CIRCULATION PATTERN OVER NORTH AMERICA FOR THE 6-10 DAY PERIOD. AN AMPLIFIED  500-HPA HEIGHT PATTERN IS FORECAST WITH RIDGING OVER THE SOUTHEASTERN CONUS,  AND TROUGHING OVER THE CENTRAL CONUS EXTENDING OVER THE SOUTHWEST. UPSTREAM,  TROUGHING IS FORECAST OVER THE BERING SEA AND A RIDGE IS PREDICTED OVER MAINLAND ALASKA AND THE NORTHWESTERN CONUS. TODAY’S MANUAL 500-HPA HEIGHT BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEANS FROM THE ECMWF, GFS, AND CANADIAN MODEL SUITES. THE RESULTANT MANUAL BLEND INDICATES ABOVE NORMAL 500-HPA HEIGHTS OVER THE SOUTHEASTERN AND NORTHWESTERN CONUS, AS WELL AS  MOST OF CENTRAL AND EASTERN ALASKA. BELOW NORMAL 500-HPA HEIGHTS ARE FORECAST OVER THE SOUTHWESTERN/CENTRAL/NORTHEASTERN CONUS, AND WESTERN ALASKA. 

RIDGING AND ABOVE NORMAL 500-HPA HEIGHTS FAVOR ABOVE NORMAL TEMPERATURES FOR THE SOUTHEASTERN CONUS WITH THE HIGHEST CONFIDENCE OVER FLORIDA. TROUGHING AND BELOW NORMAL 500-HPA HEIGHTS INCREASE CHANCES OF NEAR TO BELOW NORMAL TEMPERATURES OVER THE WESTERN AND CENTRAL CONUS, AS WELL AS PARTS OF THE NORTHEAST. NEAR TO ABOVE NORMAL TEMPERATURES ARE MOST LIKELY OVER ALASKA UNDER RIDING AND ANOMALOUS SOUTHERLY FLOW.

THERE IS A STRONG SIGNAL FOR ABOVE NORMAL PRECIPITATION ACROSS THE CENTRAL AND EASTERN CONUS DURING THE 6-10 DAY PERIOD, WITH TROUGHING IN THE CENTRAL CONUS FAVORING A FRONTAL ZONE AND A MEAN STORM TRACK THROUGH THE PLAINS, MISSISSIPPI VALLEY, AND SOUTHEAST. NEAR TO BELOW NORMAL PRECIPITATION IS MORE LIKELY FOR PARTS OF THE WESTERN CONUS, BEHIND THE PREDICTED TROUGHING OVER THE CENTRAL CONUS. ABOVE NORMAL PRECIPITATION IS LIKELY FOR MUCH OF ALASKA, IN ASSOCIATION WITH A PREDICTED TROUGH OVER THE BERING SEA. 

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, DUE TO FAIRLY GOOD AGREEMENT AMONG MODEL SOLUTIONS, WITH SOME DISAGREEMENT AMONG THE TEMPERATURE AND PRECIPITATION TOOLS.

8-14 DAY OUTLOOK FOR JAN 01 – 07 2019 

TODAY’S MODEL ENSEMBLE MEANS ARE IN GOOD AGREEMENT ON THE PREDICTED 500-HPA CIRCULATION PATTERN DURING THE 8-14 DAY PERIOD. A MODERATELY AMPLIFIED PATTERN IS FORECAST WITH RIDGING AND ABOVE NORMAL 500-HPA HEIGHTS FAVORED IN THE SOUTHEASTERN CONUS, WHILE TROUGHING AND BELOW NORMAL 500-HPA HEIGHTS ARE FORECAST IN THE CENTRAL AND NORTHEASTERN CONUS. UPSTREAM, RIDGING IS FORECAST TO DEVELOP OVER THE WESTERN CONUS WITH ABOVE NORMAL 500-HPA HEIGHTS. RIDGING IS ALSO FAVORED FOR THE ALASKA PANHANDLE AND MAINLAND ALASKA WHILE A MEAN TROUGH IS PREDICTED FARTHER TO THE WEST OVER THE BRING SEA.

ABOVE NORMAL TEMPERATURES ARE FAVORED OVER PARTS OF SOUTHEAST UNDER ABOVE NORMAL 500-HPA HEIGHTS. ENHANCED PROBABILITIES FOR BELOW NORMAL TEMPERATURES ARE MOST LIKELY OVER MUCH OF THE CENTRAL AND WESTERN CONUS UNDER THE INFLUENCE OF TROUGHING, EXCEPT FOR PARTS OF THE NORTHERN PLAINS AND THE PACIFIC COAST, WHERE NEAR NORMAL TEMPERATURES ARE INDICATED. NEAR TO ABOVE NORMAL TEMPERATURES ARE FAVORED FOR ALASKA, DUE TO ANOMALOUS SOUTHERLY FLOW AND RIDGING.

ENHANCED PROBABILITIES OF ABOVE NORMAL PRECIPITATION ARE INDICATED FOR THE EASTERN CONUS AND THE GULF OF MEXICO REGION NEAR AND AHEAD OF MEAN TROUGHING. BELOW NORMAL PRECIPITATION IS FAVORED FOR THE WESTERN CONUS UNDERNEATH NEAR TO ABOVE NORMAL 500-HPA HEIGHTS. ABOVE NORMAL PRECIPITATION IS LIKELY FOR ALASKA AHEAD OF A TROUGH PREDICTED OVER THE BRING SEA.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, DUE TO GOOD AGREEMENT AMONG MODEL SOLUTIONS, WITH SOME DISAGREEMENT AMONG THE TEMPERATURE AND PRECIPITATION TOOLS.

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON JANUARY 17.

Analogs to the NOAA 6 – 14 Day Outlook.

Now let us take a detailed look at the “Analogs”.

NOAA normally provides two sets of Analogs.

A. Analogs 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 the recent pattern is used to initialize the models to predict the 6 – 14 day Outlook.

B. There is a second set of analogs associated with the Outlook. It compares the forecast (rather than the prior period) to past weather patterns. I have not been regularly analyzing this second set of information. The first set applies to the 5 and 7 day observed pattern prior to today. The second set, relates to the correlation of the forecasted outlook 6 – 10 days out and 8 – 14 days out with similar patterns that have occurred in the past during a longer period that includes the dates covered by the 6 – 10 Day and 8 – 14 Day Outlook. The second set of analogs also has useful information as it indicates that the forecast is feasible in the sense that something like it has happened before. I am not very impressed with that approach. But in some ways both Approach A and B are somewhat similar. I conclude that if the Ocean Condition now are different then the analogs and if the state of ENSO now is different than the analogs that is a reason to have increased lack of confidence in the forecasts and vice versa.

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. But NOAA prefers the first set (A) as it helps them (or at least they think it does) assess the quality of the forecast.

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. It also helps the reader see the impact of the phases of the PDO and AMO which are shown. The first set (A) which is what I am using today applies to the 5 and 7 day observed pattern prior to today.

* I assign values that are consistent with the trend so I am doing some subjective smoothing with respect to the Phases of the AMO and PDO shown in this table. (t) = a month where the Ocean Cycle Index has just changed from a consistent pattern or does change the following month to a consistent pattern.

The spread among the analogs from December 9 to January 1, 2019 is 23 days which is similar to 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, and fairly accurate if the dates are reasonably evenly distributed, is about December 20. These analogs are centered on 3 days and 4 days ago (December 19 or December 20). So the analogs could be considered to be back in sync with respect to weather that we would normally be getting right now.

For more information on Analogs see discussion in the GEI Weather Page Glossary. For sure it is a rough measure as there are so many historical patterns but not enough to be a perfect match with current conditions. I use it mainly to see how our current conditions match against somewhat similar patterns and the ocean phases that prevailed during those prior patterns. If everything lines up I have my own measure of confidence in the NOAA forecast. Similar initial conditions should lead to similar weather. I am a mathematician so that is how I think about models.

Including duplicates, there are five El Nino Analogs, zero Neutral analogs and five La Nina Analogs. The pre-forecast analogs this week mostly argue against McCabe Condition D which is “Southwest drought extending to the North and Great Lakes”.  The opposite of McCabe Condition D is consistent with the forecast. It seems the Atlantic remains in control.

include(“/home4/aleta/public_html/pages/weather/modules/McCabe_background_information.htm”); ?>

Historical Anomaly Analysis

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

A Useful Read

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.

Some Indices of Possible Interest: We should always remember that the forecast is driven by many factors some of which are conflicting in terms of their impacts. Please pay more attention to the graphics than my commentary which does not update on a regular basis once the article is published. The indices will continue to update. I provide these indices as they are important guidelines to the weather. It is in a way looking at the factors that are impacting the weather. There were developed  because weather forecasters found them to be useful.

include (“/home4/aleta/public_html/pages/weather/modules/AO_NAO_PNA_MJO_Background_Information.htm”); ?>

We provided additional information in the introduction to this Article.

Madden Julian Oscillation (MJO)

The MJO is an area of convective activity along the Equator which circles the globe generally in 30 to 60 days. The location of the convective activity not only impacts the Equator but also the middle latitudes. Most people are not familiar with the MJO but at certain times it plays an important role Worldwide re weather and for CONUS.

There are a lot of models and I try to read the results from all of them. For access to a variety of models, I refer readers here. This weekly report summarizes things. Here is another useful source of information.

First we look at two models that I find very helpful. On the GFS graphic , the light gray shading shows the tracks which fit with 90% of the forecasts and the dark gray shading shows a smaller area that fits with 50% of the forecasts The large dot is the current location.

It is sometimes useful to look at the recent history of the MJO. We showed this graphic earlier.

Here is another way  of looking at this information through time with a Hovmoeller graphic.

Then the first of the two indices we typically present.

This shows the recent history.  MJO now in Phase 5.

And then a forecast.

Remember we are interested in how the MJO impacts CONUS weather during early January. So I have displayed the DJF information this week.  Over the next two weeks, Phases 5 and 6 may be experienced.

Temperature

Precipitation

Recent CONUS Weather

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

And the 30 Days ending December 15, 2018	And the 30 Days ending December 22, 2018
The biggest change is the moderation of the Eastern cool anomaly and the slight increase in the Western warm anomaly	The precipitation pattern did not change much but the temperature anomaly switched form cold east to warm west….this is the west to east movement of large troughs/
Remember, these maps are 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

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 early January and we should be returning from the set of positions shown below for July back slowly to the Winter Pattern. For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant.

World Forecasts

1. Today (Source: University of Maine)

2. Short-term set for day six but can be adjusted (BOM – Australia)

3. 8 – 14 Day (NOAA/Canada/Mexico Experimental NAEFS))

4 Tropical  Activity

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

And now precipitation

Additional Maps showing different weather variables can be found here.

2. 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

Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader.

Now Precipitation

3. And now we have experimental 8 – 14 Day World forecasts from the NAEFS Model.

First Temperature

Then Precipitation

4. Tropical Hazards.

C. ENSO SUMMARY of Current Status. Our full report was published on November 20, 1018 and can be accessed here.

Current Status of ENSO

This section is organized into three parts.

1. Current Sea Surface Temperatures (SST)

2. Current Nino 3.4 Readings

3. The Surface Air Pressure Pattern that confirms the state of ENSO.

1. Current and Recent Sea Surface Temperatures (SST)

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.

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

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.

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

First the categorization of the current daily SST anomalies.
Mediterranean, Black Sea and Caspian Sea	Western Pacific	West of North America	North and East of North America	North Atlantic
The Mediterranean. Black Sea and Caspian Sea are mostly Neutral	Warm south of Japan.	Fairly Neutral which is unusual	Mostly Neutral Warm Davis Strait.	Slightly warm north of Scandinavia.
Equator	Looks like El Nino but Barely
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Slightly cool off West Africa extending out to sea. Warm south of South Africa Cool Gulf of Guinea	Neutral.	Cool to North and Northwest. Warm to the Southeast but offshore and beyond New Zealand.	Fairly Neutral	Warm off  30S Warm off 50S.

Then we look at the change in the anomalies. The SST anomaly is sort of like the first derivative and the change in the anomaly is somewhat like a second derivative. It tells us if the anomaly is becoming more or less intense.

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 graphic form but going back a couple of more years can be found here. The full table of values can be found here. NOAA considers Nino 3.4 shown in the graphic as the best indicator of Equatorial Surface Temperature Anomalies associated with different phases of ENSO. There is a duration requirement to be a recorded El Nino or La Nina but to have El Nino Conditions the Nino 3.4 index needs to be +0.5C or warmer and to have La Nina Conditions the Nino 3.4 Index needs to be -0.5C or cooler.

This graphic brings the Nino 3.4 up to date and is easy to read.

Here is a daily version

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.

3. The Surface Air Pressure that Confirms the Nino 3.4 Index

And of course Queensland Australia is the official keeper of the SOI measurements.

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).

D. Putting it all Together.

At this time, La Nina Conditions along the Equator have come to an end and we are solidly into ENSO Neutral and possibly entering into El Nino Conditions. But the drivers of a transition to El Nino are not solidly in place. In fact this is almost unprecedented in terms of the lateness of the arrival of a potential El Nino. If an El Nino it will be where the Peak Value of the Nino 3.4 Index will be achieved early on and will be in decline the rest of the time which has different impacts than an El Nino with a stable Nino 3.4 Index.

E. Relevant Recent Articles and Reports

Updated ONI History

F. Useful Reference Information

Understand How the Jet Stream Impacts Weather

include(“/home4/aleta/public_html/pages/weather/modules/Jet_Streak_Four_Quadrant_Analysis.htm”); ?>

include(“/home4/aleta/public_html/pages/weather/modules/MJO_and_ENSO_Interaction_Matrix.htm”); ?>

Standard Pressure Levels

include(“/home4/aleta/public_html/pages/weather/modules/Standard_Pressure_surfaces.htm”); ?> include(“/home4/aleta/public_html/pages/weather/modules/Table_of_Contents_for_Part_II.htm”); ?>