April 16, 2018 Weather and Climate Report – NOAA Clings to La Nina Designation

Written by Sig Silber

Odd decision to say the least, but the weather lags ENSO phase so perhaps that is their reasoning. In other news, the general pattern will turn drier for much of CONUS after the next two Pacific Storms cross the U.S. This will reduce the number of baseball rain delays and postponements. But prediction confidence for Days 8 – 14 is low at this time.

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This Australian graphic brings the Nino 3.4 up to date and is easy to read. It may be more reliable than the NOAA readings.

NOAA Graphic (This is a legacy system but should be accurate)

Because we are still having snowy weather, we make it easy to get a snow forecast. This is the six-hour snow forecast.

Looking further out.

NOAA Snow Forecast looking ahead to Days 4, 5 (top Row) 6 and 7 (bottom row). When you view these graphics you can click on them to enlarge them.

A. Now we return to our regular approach and 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. I have include the best graphic I have for the Day 1 -5 Period.

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.			It is difficult to compare this with the other maps that show deviation from climatology as we expect the north to be cooler than the south. But it does seem to be consistent with the 6 – 10 day map. You can  see the 40F+ difference between North and South but this is less of a difference than for the past two weeks.
		Click to Enlarge
		Transitioning from the 6 to 10 day outlook on the left (also called Week One) to the 8 to 14 day outlook (Week Two) on the right   →
		The pattern is fairly stagnant but becomes less amplified in the second week.
To the right is the week 3 and 4 Forecast.                                                   → There is a warm anomaly for Alaska. There is a CONUS western warm anomaly and an eastern cool anomaly that does not reach to the Gulf Coast and indeed for Florida it is a warm anomaly.			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems feasible.

then Precipitation

The five day QPF is shown to the right. The units are different than the other maps i.e. in units of precipitation (inches) not probabilities of exceeding or being less than climatology.			It is difficult to compare this with the  other maps as some places are naturally more wet than others. But it seems to be somewhat consistent with the 6 – 10 day map and this is a Day 1 – 5 Map and the precipitation pattern for Days 6 – 10 may be very different.
		Transitioning from the 6 to 10 day outlook on the left to the 8 to 14 day outlook on the right.     →
		The precipitation pattern, unlike the temperature pattern, is progressive west to east. I am not sold on the forecast for New Mexico. .
To the right is the week 3 and 4 Experimental Forecast.    →                Northwest Alaska is dry. For the Southern Tier it is mostly dry from West Texas to the west. The Western dry anomaly is a bit further north than recently and may signify an early Monsoon.			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left does not seem feasible. It is unlikely that they are both correct.

 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.

You can see from this animation that we have the same pattern of moisture entering the Northwest and also crossing Mexico and entering CONUS from there.

Tonight, Monday evening April 16, 2018, as I am looking at the above graphic, you see the the same pattern but with less actiivty in 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.

And Now the Day One and Two CONUS Forecasts

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.

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. You can see the next East Coast Nor’easter.

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.

When I look at this Day 7 forecast, there is a Low in the Gulf of Alaska with surface central pressure of  1004 hPa. To the west there is a Low east of Kamchatka with a surface central pressure of 992 hPa. Further east there is a Ridge with surface central pressure of 1028 hPa, and then a Low near Hudson Bay with surface central pressure of 1008 hPa and then further east a High with surface central pressure of 1028 hPa. Thus there is a succession of Highs and Lows moving from west to east. This week, the Hawaiian High with surface central pressure of 1024 hPa and extending on shore will play a decisive role in blocking storms after Day 7 from tracking down offshore of California but forcing them to stay north or travel down the Great Basin. There is a Low near the Gulf Coast with central surface pressure of 1008. NOAA seems to believe it will be a major player in the weather pattern.

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.

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.
You can see the Hawaiian High staying south possibly to bring warm dry weather to the Southwest. The graphics update when NOAA updates their graphics so it will be interesting to watch the development of these Lows. Things to look for in general 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
We still seem to have a split Polar Jet Stream with Northern and Southern Branches. The current deep dive shown raises questions about frost and violent weather at the base of this trough as it sweeps east.

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. 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.

Here is the whole suite of similar maps for Days 3, 4, 5, 6 and repeated for Day 7. 

Day 3 Above, 6 Below	Day 4 Above,7 Below	Day 5 Above.

Here is the seven-day cumulative precipitation forecast. More information 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 April 16, 2018 was 3 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on April 16, 2018 was 2 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 April 16, 2018 was 3 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on April 16, 2018 was 2 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today April 16, 2018 and the Week 3/4 discussion released Friday April 13, 2018

6-10 DAY OUTLOOK FOR APR 22 – 26 2018  

TODAY’S VARIOUS ENSEMBLE MEAN SOLUTIONS ARE IN FAIR AGREEMENT ON THE 6-10 DAY  FORECAST PATTERN OVER THE FORECAST DOMAIN. THE MANUAL BLEND AT 500-HPA FORECASTS AN ANOMALOUS TROUGH OVER THE BERING SEA AND WESTERN MAINLAND ALASKA, AND POSITIVE HEIGHT ANOMALIES OVER MUCH OF THE CONUS. TODAY’S MANUAL 500-HPA BLEND SLIGHTLY FAVORS THE 0Z ECMWF ENSEMBLE MEAN, DUE TO ITS HIGHER RECENT 500-HPA FORECAST SKILL.

BELOW NORMAL TEMPERATURES ARE FAVORED ACROSS THE CENTRAL AND EASTERN CONUS, DUE TO THE PASSAGE OF SEVERAL COLD FRONTS AND ANOMALOUS SNOW COVER OVER THE UPPER MISSISSIPPI VALLEY. ABOVE NORMAL TEMPERATURES ARE FAVORED OVER THE MOST OF WESTERN CONUS, WHERE NEAR TO ABOVE NORMAL HEIGHTS ARE PREDICTED. ABOVE NORMAL TEMPERATURES ARE SLIGHTLY FAVORED IN SOUTHWESTERN PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS, CONSISTENT WITH REFORECAST-CALIBRATED GEFS AND ECMWF TOOLS.  

MUCH OF THE WESTERN CONUS, THE UPPER MISSISSIPPI VALLEY AND PARTS OF THE GREAT LAKES AND THE NORTHEAST ARE EXPECTED TO REMAIN RELATIVELY DRY, CONSISTENT WITH DYNAMICAL FORECAST TOOLS. A SHORTWAVE TROUGH EJECTING FROM THE SOUTH-CENTRAL CONUS FAVORS ABOVE NORMAL PRECIPITATION OVER THE LOWER MISSISSIPPI VALLEY, SOUTHEAST, AND MID-ATLANTIC. SEVERAL PREDICTED STORM SYSTEMS IN THE GULF OF ALASKA INCREASE THE LIKELIHOOD OF ABOVE NORMAL PRECIPITATION FOR THE SOUTH COAST OF MAINLAND ALASKA, THE ALASKA PENINSULA AND THE ALEUTIANS.   

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: NEAR AVERAGE, 3 OUT OF 5, DUE TO FAIR OVERALL AGREEMENT AMONG THE AVAILABLE FORECAST TOOLS.  

8-14 DAY OUTLOOK FOR APR 24 – 30 2018   

THE FORECAST 500-HPA HEIGHT PATTERN FOR WEEK-2 IS SIMILAR TO 6-10 DAY FORECAST PATTERN AND RELATIVELY LOW AMPLITUDE, LIKELY DUE TO INCREASED ENSEMBLE SPREAD IN THE WEEK-2 PERIOD.  

GENERALLY THE TEMPERATURE PROBABILITY FORECAST DURING THE WEEK-2 PERIOD IS SIMILAR TO THE 6-10 DAY PERIOD, EXCEPT THAT ANOMALOUS LOW LEVEL NORTHERLY FLOW  OVER THE NORTH-CENTRAL CONUS IS LESS LIKELY AND ABOVE NORMAL HEIGHTS OVER PARTS  OF THE NORTHEAST ENHANCE THE PROBABILITIES OF NEAR TO ABOVE NORMAL TEMPERATURES FOR THESE AREAS.

MUCH OF THE NORTHWESTERN CONUS IS PREDICTED TO REMAIN RELATIVELY DRY, CONSISTENT WITH DYNAMICAL FORECAST TOOLS. THE PREDICTED STORM TRACK IN THE  CENTRAL AND SOUTHERN PLAINS AND MUCH OF THE EAST COAST INCREASE PROBABILITIES  OF ABOVE NORMAL PRECIPITATION THERE. BELOW NORMAL PRECIPITATION IS FAVORED IN  PARTS OF THE LOWER MISSISSIPPI, TENNESSEE AND OHIO VALLEYS AND THE SOUTHEASTERN  U.S., CONSISTENT WITH DYNAMICAL FORECAST TOOLS. SEVERAL STORM SYSTEMS FORECAST OVER THE GULF OF ALASKA ENHANCE PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR  THE SOUTH COAST OF MAINLAND ALASKA, THE ALASKA PENINSULA AND THE ALEUTIANS.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO  FAIRLY POOR MODEL AGREEMENT WITH A RELATIVELY LOW-AMPLITUDE CIRCULATION PATTERN

Week 3-4 Forecast Discussion Valid Sat Apr 28 2018-Fri May 11 2018

La Nina conditions currently are present across the equatorial Pacific Ocean. Equatorial sea surface temperatures (SSTs) are below average across the east-central and eastern Pacific Ocean. Both the La Nina and the coupled atmospheric response to this cold event weakened in recent weeks. The CPC velocity potential based and RMM MJO indices indicate a strong MJO signal moved across the Western Hemisphere and into Africa within the past few days. The GEFS forecasts MJO to remain active across Africa and the Indian Ocean, then some weakening and continued rapid propagation during Week-2. The Week 3-4 temperature and precipitation outlooks rely primarily on dynamical model forecasts from the NCEP CFS, ECMWF, and JMA operational ensemble prediction systems, as well as forecasts from the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of experimental ensemble prediction systems. Consideration is also given to the possible evolution of the predicted circulation pattern for Week-2.

The various model guidance supporting the Week 3-4 outlook is in fair agreement today, depicting troughs over the Aleutians and eastern CONUS. The CFS and ECMWF ensemble means favor below-normal 500-hPa heights over most of the eastern CONUS and the Aleutians, while near- to above-normal 500-hPa heights are indicated over western CONUS. The CFS and ECMWF favor near-normal 500-hPa heights over Hawaii, while the JMA predicts above-normal 500-hPa heights over Hawaii.

Near- to above-normal 500-hPa heights enhance probabilities for above-normal temperatures for the western and southwestern CONUS. Anomalous troughing and below-normal 500-hPa heights tilt the odds to below-normal temperatures for most of the central and eastern CONUS, except for southern Florida where above-normal temperatures are indicated. This pattern is also supported by dynamical model temperature guidance tools (CFS and ECMWF). Calibrated temperature forecasts from the individual models and multi-model combinations of these forecasts also favor above-normal temperatures for Alaska, consistent with dynamical model guidance from SubX.

The various guidance is in fair agreement on the precipitation outlook. Anomalous troughing and below-normal 500-hPa heights lead to increased chances for near- to above-median precipitation for parts of the southeastern CONUS. Calibrated precipitation forecasts from the individual models and multi-model combinations of these forecasts favor below-median precipitation over parts of the Upper Mississippi Valley and Upper Great Lakes areas and the southwestern CONUS. As with the Desert Southwest, the North Slope is given equal-chances here as it is typically arid and models anticipate no precipitation, thus both below- and above-median precipitation are unreasonable forecasts. [Editor’s Note: True but sad]

Observed sea surface temperatures are warm in the vicinity of Hawaii, tilting odds towards above-normal temperatures. Dynamical model guidance from CFS, ECMWF and JMA precipitation forecasts indicates increased probabilities of above-median precipitation for Kahului and Honolulu during the Week 3-4 period.

Some Indices of Possible Interest:

Madden Julian Oscillation (MJO)

NCEP-NEFS	CFSv2

Analogs to the 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.

Last week NOAA was shuffling around some of their files so they only provided the second set of analogs so that is what I used last week. This week I have the set (A) that I prefer so here goes.

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. The first set (A) which is what I am using today applies to the 5 and 7 day observed pattern prior to today.

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

The spread among the analogs from April 5 to April 20 is 15 days which is very very tight. 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 April 8. These analogs are centered on 3 days and 4 days ago (April 12 or April 13). So the analogs could be considered to be way out of sync with respect to weather that we would normally be getting right now namely close to a week later than  we would expect. This is now a slightly delayed Spring.

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 six Neutral Analogs, two La Nina analogs and two El Nino Analogs. The pre-forecast analogs this week do strongly favor McCabe C and to a lesser extent McCabe D. The both are western drought scenarios one with the drought to the north, the other with the drought to the south. They both are correlated with AMO Positive. This is consistent with the NOAA forecast.

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

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.

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.

Recent CONUS Weather

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

And the 30 Days ending  March 31, 2018	And the 30 Days ending April  7, 2018
Not very much change in the precipitation pattern nor in the   temperature pattern but an overall shift to a cooler regime at least in terms of anomalies.	Not much change in the precipitation pattern, the temperature cold anomaly is more intense.
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

The U.S. Drought Monitor is a comprehensive way of understand the drought situation for the U.S. If is issued every Thursday and reflects the conditions as of the prior Tuesday. The drought monitor is not just based on precipitation but the condition of the land so it generally reflects more than a month’s precipitation and temperature and wind.

Because of the current drought conditions we now publish a Drought Update on Thursdays. You can access the most recent report here.  But notice the doubling of the size of area designated as D3.

Below are the Temperature followed by the Precipitation Outlooks for the month and three months shown in the Legend. These maps 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.

	To the left is the full month Temperature Outlook. To the right is the three-month Temperature outlook
	To the left is the full month Precipitation outlook. To the right is the three-month Precipitation outlook.

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 in the second half of April and should be returning to the set of positions shown below for July (and that appears to be happening at least in the Pacific).For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant. Notice the Winter position of the Pacific High (Hawaiian High). It has been further north than usual for this time of the year. But it is forecast to drop down closer to its usual position

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

Temperature.	Precipitation.
Not a lot of surprises here.  But Equatorial Africa is very warm.	We again see the dry belt stretching from Northern Africa to Eastern Asia now including part of Southeast Asia. But it does not seem as well defined as all Winter. The Southern Hemisphere is very 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

And now we have experimental forecasts from the U.S. NAEFS Model. They are difficult to read without first enlarging them.

Looking Out a Few Months

Here is the precipitation forecast from Queensland Australia:

It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. But the current reading of the SOI is probably more impacted by the SOI than ENSO so its predictive value out three months is questionable.

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 to 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
La Nina shows up	The cool anomaly is displaced to the west a bit. We see a lot of white where we used to see blue.

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 current daily SST anomalies.
Mediterranean, Black Sea and Caspian Sea	Western Pacific	West of North America	North and East of North America	North Atlantic
Fairly neutral Persian Gulf and Norther Arabian Sea warm.	Mixed along eastern coast of Asia; Warm south of Anadyr Cool off of Indochina	Slightly Warm Bering Sea Warm off Baja but offshore and stretching to the Dateline.	Warm off Nova Scotia Very-slightly Warm Northern Gulf of Mexico	Warm north of British Isles.
Equator	The La Nina cool anomaly is displaced to the west and exists only south of Equator.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Mixed south and southeast of Africa	Mostly neutral	Warm to the north . Slightly warm to the east and beyond New Zealand	Cool off Ecuador Cool off 60S	Warm off 30S to 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.

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
Eastern Mediterranean warming	Warming around Japan Cooling off Indochina Warming North of Australia	Warming offshore of Baja and Central America .	Fairly Neutral	Cooling around British Isles .  .
Equator	Eastern Pacific consistently extreme warming to the east except right along the South America Coast.  Cooling in the eastern Indian Ocean  warming to the west.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cooling off North Africa Warming east of Africa and engulfing Madagascar	Mostly neutral	Warming north	Sleight cooling off Ecuador and Peru	Warming east of 30S

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. Notice the change in the PDO in July of 2017 and the stability of the AMO index.

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

 * 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.

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.

Location Bar for Nino 3.4 Area Above and Below

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 April 16, in the afternoon working from the April 15 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

My estimate of the daily Nino 3.4 SST anomaly tonight is again -0.3 which is an ENSO Neutral not a La Nina value. NOAA has reported the weekly Nino 3.4 to be warmer than last week at -0.4 which is an ENSO Neutral value not a La Nina value. Nino 4 is reported to be warmer than last week at 0.0. Nino 3 is reported as the same at -0.3. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported a bit cooler at -1.3. It was up there close to -3.0 at one time so this index has been declining as an anomaly (rising) 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 graphic form but going back a couple of more years can be found here.  The full table of values can be found here.

This graphic brings the Nino 3.4 up to date and is easy to read. It may be more reliable than the NOAA readings.

Here is another way of looking at the TAO/TRITON Graphic. It is a fast way to assess the strength of an ENSO Event and provides a way to track it.  

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

The next graphic overlaps with the subsequent topic but I will show it here.

The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2017. The anomaly had returned to zero then reversed for a month and then returned to zero and now has gone positive. In retrospect it was the Kelvin Wave (#1) Activity the Upwelling Phase and the MJO which caused the brief reversal of the warming trend.

A side by side comparison can be useful

Comparison Week Probably Third Week of December 2017	Current 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.

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.

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

We are back to a single Kelvin Wave phase in operation. The up-welling phase of Wave #1 reached South America and is no longer a factor re the Nino 3.4 Measurement Area but is a factor further east.. The down-welling phase of Wave #2 is at the 120W. The down-welling phase will provide the warm water to end this La Nina and in our opinion already has.

 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).

.

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. These currents are very complicated and made even more so by the uneven nature of the ocean floor. So the exact pattern of where this warm water will erupt is beyond my level of understanding. But it will erupt to the surface in multiple different places.

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 neutral water from the Dateline to 110W and spotty but colder to the east. We now have warm water with a maximum anomaly of +4C developing west of the Dateline and crossing the Dateline at depth to 110W, the result of another Down-welling Kelvin Wave: Wave #2. La Nina is over but its demise is not yet acknowledged by NOAA.

The 28C Isotherm is at the Dateline, the 27C Isotherm is at 160W, the 25C Isotherm is now at100W and in many places at the surface further east. The 20C Isotherm is no longer close to reaching the surface.

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 an ENSO Neutral thermocline.

Tracking the change.

And now let us look at the atmosphere.

This graphic shows the 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 tell us where convection has been taking place. The bottom of a Hovmoeller graphic shows the most recent readings.
Reds and browns would be suppressed easterlies or enhanced westerlies and are typical of El Nino. You see the recent change in the pattern.	We see the change in the pattern of suppressed OLR as the MJO moves through and the La Nina declines.

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

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

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.

Here is the most recent update.

IRI ENSO Forecast CPC/IRI ENSO Update Published: April 12, 2018 El Niño/Southern Oscillation (ENSO) Diagnostic Discussion issued jointly by the Climate Prediction Center/NCEP/NWS and the International Research Institute for Climate and Society ENSO Alert System Status: La Niña Advisory

Synopsis: La Niña is expected to transition to ENSO-neutral during April-May, with ENSO-neutral then likely (greater than 50% chance) to continue through the Northern Hemisphere summer 2018.

During March 2018, La Niña continued to weaken, but was still reflected by below-average sea surface temperatures (SSTs) across the east-central and eastern equatorial Pacific Ocean. The latest weekly index values were -0.5°C and -0.3°C in the Niño-3.4 and Niño-3 regions, respectively, -1.1°C in the Niño1+2 region, and near zero in the Niño.4 region. While negative anomalies were weakening near the surface, the sub-surface temperature anomalies (averaged across 180°-100°W) warmed  due to the eastward propagation of a downwelling equatorial oceanic Kelvin wave. Convection was suppressed near and east of the Date Line and enhanced over the far western tropical Pacific Ocean. Low-level wind anomalies were easterly over the east-central Pacific, and westerly over the far western Pacific. At upper-levels, winds were anomalously westerly over the eastern Pacific. Overall, the ocean and atmosphere system remained consistent with a weak La Niña.

Most models in the IRI/CPC plume predict La Niña will decay and return to ENSO-neutral during the current March-May season 2018. The forecaster consensus similarly favors a transition to neutral, with a continuation of ENSO-neutral conditions through the summer 2018. Thereafter, there is considerable forecast uncertainty, in part due to the lower prediction skill for forecasts made at this time of year. In summary, La Niña is expected to transition to ENSO-neutral during April-May, with ENSO-neutral then likely (greater than 50% chance) to continue through the Northern Hemisphere summer 2018 (see the CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum section of CPC’s Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog.

The next ENSO Diagnostics Discussion is scheduled for 10 May 2018. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: [email protected].

Climate Prediction Center National Centers for Environmental Prediction  NOAA/National Weather Service College Park, MD 20740

The above is based on looking at a variety of models and other information but we should not forget that NOAA has their own model.

Here is another view of the same model with on the right the forecasts of the sea surface temperatures that result from the forecast. It is the model as of January 14 and is frozen i.e. will not update.

And here is what is called the plume of a varied of forecast models. We expect to have an updated version of this graphic on Thursday.

Forecasts from Other Meteorological Agencies.

Here is the JAMSTEC Model Forecast

And the recently released short discussion.

Mar. 16, 2018. Prediction from 1st Mar., 2018 ENSO forecast:

The La Niña-like condition will disappear by late spring. 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 in 2018.

Atlantic Ocean forecast:

The Atlantic Niño appears to develop in 2018.

Regional forecast:

On a seasonal scale, most part of the Eurasian Continent will experience a warmer-than-normal condition in spring and summer. In India, however, we expect colder-than-normal condition in summer. Northwestern U.S., western Canada, northern Brazil, Peru, Ecuador, western, eastern and southern Africa, and northern Australia will experience a colder-than-normal condition in boreal spring. This colder condition in northern Brazil and southern Africa will stay even in boreal summer.

As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for the Philippines, Indochina, northern India, eastern Africa, Mexico, eastern U.S. and northern Brazil during boreal spring, whereas western/central U.S., Europe, Iran, Indonesia, southern China, Australia, southern Africa, and southern Brazil will experience a drier-than-normal condition during boreal spring. This drier condition will stay in Europe, central U.S., southeastern Australia, and Indonesia in summer.

Most part of Japan will experience warmer and wetter-than-normal conditions in spring and summer; we expect an active rainy season in 2018.

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

And the ENSO Outlook Discussion Issued on April 10, 2018

El Niño–Southern Oscillation influence on the climate remains weak

The El Niño–Southern Oscillation (ENSO) remains neutral—neither El Niño nor La Niña. Most models predict a neutral ENSO pattern will persist through the southern autumn and winter.

Most atmospheric and oceanic indicators of ENSO are at neutral levels. Sea surface temperatures in the central Pacific are close to average for this time of year. Beneath the surface, the tropical Pacific Ocean is slightly warmer than average, but well within the neutral range. In the atmosphere, cloud and pressure patterns remain weakly La Niña-like, but trade winds are close to average.

Climate models indicate that tropical Pacific Ocean sea surface temperatures will continue to rise, but remain ENSO neutral for the remainder of the southern autumn and winter.

All eight of the surveyed international climate models indicate equatorial Pacific sea surface temperatures are likely to continue rising over the coming months. A neutral ENSO state is the most likely outcome for the remainder of the southern hemisphere autumn and winter. The Bureau’s model predicts the equatorial Pacific will continue to gradually warm throughout winter but remain within the neutral range.

Climate model outlooks for ENSO and the IOD have lower accuracy during autumn than at other times of the year. Hence, current model outlooks of these climate drivers should be viewed with some caution.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole Outlook  Discussion Issued April 10, 2018

The Indian Ocean Dipole (IOD) is currently neutral with a weekly index value to 8 April of +0.2 °C. All of the six international climate models surveyed by the Bureau indicate that the IOD will remain neutral during autumn. However, two models, including the Bureau’s model, suggest that a negative IOD event is possible during the southern hemisphere winter. It should be noted that outlook skill is lower at this time of year.

A negative IOD during winter tends to enhance rainfall across southern Australia..

The IOD Forecast is indirectly related to ENSO but in a complex way. It is important to understand how and where the IOD is measured.

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 that La Nina Conditions along the Equator have come to an end. The actual impacts on Worldwide weather lag the change in conditions along the Equator so we will have impacts from this La Nina for one or two more months.

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. 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 and it is probably three or more years out.

E. Relevant Recent Articles and Reports

Weather in the News  

Weekend Spring Storm

Note these are forecasts made last Thursday and covered this past weekend and are presented only as a matter of interest and are excerpted from the above Category 6 Article.

MLB Rainouts at High Level

Midwest Snow

Weather Research in the News

Nothing to report

Global Warming in the News

Nothing to report

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

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

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

2. Medium Frequency Cycles such as ENSO and IOD

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

4. Computer Models and Methodologies

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

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

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

1. Introduction

2. Climate Impacts of Global Warming

3. Economic Impacts of Global Warming

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

H. Useful Background Information

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

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.

Click for Source

Interaction between the MJO and ENSO

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

History of ENSO Events as measured by the ONI

The new SON reading of -0.8 is the fifth La Nina Reading. Not all Meteorological Agencies Worldwide will necessarily accept this La Nina to be legitimately declared but most will. 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. It would apply to the states that are at the apex of the trough.

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.]

Here is a time sequence animation. You may have to click on them to get the animation going.

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.

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.

Tropical Activity Possibly Impacting CONUS.

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.

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.