February 26, 2018 Weather and Climate Report – Change in Pattern

Written by Sig Silber

There has been a dramatic change in the pattern of Highs and Lows which may be a result of the shifting west of the core of the dying La Nina which is now located way offshore of Ecuador. It is clearly related to the westward shift in the location of the Planetary Wave which we reported on last week. The passing of the Active Phase of the MJO may also be part of what is happening. All in all, conditions lead to low confidence in the NOAA 6 to 14 Day Forecast with respect to precipitation. Keep reading to learn more about this and also the JAMSTEC forecast of an Atlantic Nino.

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

Pattern Change

La Nina Modoki

I am not going to try to explain a La Nina Modoki. It is complicated relative to the impact on CONUS as opposed to the Coast of Asia and I am not sure that we really have a La Nina Modoki but it is westerly displaced that is for sure. Whether or not that has led to the Hawaiian High retrograding to the West I just do not know.

Notice instead of a La Nina cold tongue extending from Ecuador, we now have more of an El Nino warm tongue. But I think this is a transition state rather than a true La Nina Modoki so that is all I am going to say about it but instead focus on this from the JAMSTEC discussion which we published last Monday (and again today).

Atlantic Ocean forecast:

The Atlantic Niño and the Benguela Niño [Editor’s Note: Benguela Current which when warmed has lees upwelling and thus becomes less nutrient rich] appear to develop in 2018.

What are they talking about?

This is the JAMSTEC explanation of “El Nino’s Little Brother”. This Wikipedia discussion is good also especially in regards to the impact of the Atlantic Nino on Western Equatorial Africa. And one more that shows that we do not really understand this ENSO like pattern in the Atlantic.  And then there is the very important Nnamchi et al paper which addresses the question of whether or not the Atlantic Nino and the South Atlantic Ocean (SAO), also peaking in boreal summer and termed the SAO dipole (SAOD) are related. And of course we should never ignore the paper written by Michael McPhaden and his co-author Joke Lubbecke where the differences between the Pacific ENSO and Atlantic Nino are quantified. There is a lot written about this relatively “unknown” pattern. Part of the reason may be that this pattern which has been know at least since 1996 and probably before then is not well enough understood to enter public discourse and probably also because it mostly impacts African weather and fisheries not CONUS but it may as it may impact the formation of hurricanes.

First we need to consider where it is measured.

Notice the trigger for the Atlantic Nino is a 0.4 C warm anomaly where for ENSO the trigger is plus or minus 0.5 C. But Australia uses 0.8C. In general the variation in the Atlantic is 1/2 to 1.3 of the variation during the Pacific ENSO Cycle. This is mostly because the Pacific is so much wider than the Atlantic. And of interest the ENSO Cycle is mostly about winter and the Atlantic Nino is mostly about Spring and Summer. And from the JAMSTEC write up, a short description of what the Atlantic Nino is

This all has to do with the weakening of the Easterlies. So in that sense it is very similar to the ENSO cycle in the Pacific. Some say the magnitude of this cycle is 1/2 to 1.3 of the magnitude of El Nino and the impacts are difficult to observe except just east of the ATL

And from the Wikipedia Article a description of the impacts inland from the Gulf of Guinea.

Impact on African Climate

Warming or cooling of the equatorial oceans has understandable consequences for atmospheric climate. The equatorial oceans comprise a major portion of the overall heat budget and, therefore, alter convective regimes near the equator. In the case of the Pacific El Niño, enhanced convection over the central Pacific and reduced convection over the Maritime Continent fundamentally change climate not just in the tropics, but globally. Since the Atlantic Niño is physically similar to ENSO, we might expect climate impacts from it as well. However, given its reduced size both spatially (the Atlantic basin is much smaller than the Pacific basin) and in magnitude, the climate impacts of the Atlantic Niño are best seen in the tropical and subtropical regions nearest to the equatorial Atlantic

The impact of the Atlantic Niño on African climate can be best understood by assessing how above normal equatorial sea surface temperatures impact the seasonal migration of the Intertropical Convergence Zone (ITCZ). Warm equatorial sea surface temperatures lower surface air pressure which induces more equatorward flow than normal. This, in turn, prevents the ITCZ from migrating as far north as it would under normal conditions during the summer, reducing rainfall in the semi-arid Sahel to the north, and increasing rainfall in regions along the Gulf of Guinea. Increased rainfall relative to normal is typically associated with negative temperature anomalies over these tropical land areas. Some evidence suggests that a warming trend in Indian Ocean equatorial sea surface temperatures contributes to long-term drying of the Sahel, which is exacerbated by periodic warming of the equatorial Atlantic related to the Atlantic Niño. In fact, the ability to predict the Atlantic Niño is a major research question given its impact on seasonal climate.

So let us take a look at the JAMSTEC precipitation forecast for MAM and JJA.

	MAM	JJA
SST
Precipitation
Temperature

You can see the dry north, wet south pattern in MAM and the change into one of all wet in JJA.

Let’s change the subject.

Because it is Winter 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.

First Temperature

		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 progressive. It is looking more like the JAMSTEC forecast.
To the right is the week 3 and 4 Forecast. There is a cool anomaly in Southern Alaska, the Alaskan Panhandle and Northwest CONUS. There is a warm anomaly covering a narrow strip of the Southern Tier of CONUS and a Great Lakes and Northeast warm anomaly.                   →			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left seems feasible.

And then Precipitation

		Transitioning from the 6 to 10 day outlook on the left to the 8 to 14 day outlook on the right.                                         →
		A continuation of the pattern into the second week (Days 8 – 14).
To the right is the week 3 and 4 Experimental Forecast.    →                Northeast Alaska is wet and Southern and Western Alaska are dry but south of that it is wet extending down into a narrow strip of the West Coast. Florida also has a wet anomaly and the Northeast is Dry and Texas, Oklahoma and SE New Mexico have the dry anomaly forecast.			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left seems feasible.

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

Water Vapor.

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

You can see from this animation, moisture is entering North America in the Northwest and also streaming in through Mexico but further south than last week. Below is the same graphic as above but without the animation to show the current situation with respect to water vapor imagery for Western North America.

Tonight, Monday evening February 26, 2018, as I am looking at the above graphic, you see a pattern of light moisture entering California and also moisture entering Texas via Mexico.

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.

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 large Low west of the Aleutians and east of Kamchatka with surface central pressure of 1008 hPa. The Aleutian Low is out of position to impact anything but Alaska. There is now a large High (last week it was a Low) north of Hudson Bay with surface central pressure of 1036hPa. And very critical is the Pacific Subtropical High with surface central pressure of 1036 hPa. This High is out of position out to sea and between it and land there is a Low with surface central pressure of 1016 i.e. a very weak Low. Inland there is a High with surface central pressure of 1028 hPa. The Bermuda High off the East Coast is not there and instead there is a Low with surface central pressure of 988 hPa.

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.
There is not a lot of change in the pattern over the five days shown. The High has retrograded offshore enough to allow troughs to form in the Great Basin. In fact it is far enough offshore for there to be a weak Low between it and the Coast. 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. As the MJO moves out of range this splitting is likely to increase. You can not really see from this graphic but the Northern Branch is going up and over Alaska and then dropping down into the Gulf of Alaska and paralleling British Columbia and then impacting CONUS. You can see the current trough being mostly interior to the Jet Stream. But the trough is not extending very far south.

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. 

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 February 26 was 2 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on February 26, 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 February 26, 2018 was 2 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on February 26, 2018 was 2 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today February 26, 2018 and the Week 3/4 (assumption rich) discussion released Friday February 23, 2018

6-10 DAY OUTLOOK FOR MAR 04 – 08 2018

TODAY’S MODEL SOLUTIONS FEATURE STRONG POSITIVE 500-HPA ANOMALIES AT HIGH LATITUDES CONSISTENT WITH A NEGATIVE AO PATTERN. RIDGES ARE PREDICTED SOUTH OF THE ALEUTIANS AS WELL AS OVER EASTERN CANADA CENTERED OVER OR JUST TO THE NORTH OF NORTHERN QUEBEC. FARTHER TO THE SOUTH, NEAR TO BELOW NORMAL HEIGHTS ARE EXPECTED FOR MUCH OF THE CONUS AS A TROUGH OVER THE WESTERN CONUS EARLY IN THE PERIOD PROGRESSES TOWARD THE EASTERN CONUS LATER IN THE PERIOD. SLIGHTLY POSITIVE HEIGHTS ARE INDICATED FOR PARTS OF THE SOUTHWESTERN CONUS AS HEIGHTS RISE IN ADVANCE OF A TROUGH OVER THE EASTERN PACIFIC LATE IN THE PERIOD. POSITIVE HEIGHT ANOMALIES ARE ALSO EXPECTED FOR PARTS OF THE GREAT LAKES AND NORTHEAST IN ASSOCIATION WITH THE MEAN RIDGE OVER EASTERN CANADA. ENSEMBLE SPREAD IS VERY HIGH OVER MUCH OF THE FORECAST DOMAIN, LEADING TO LOWER THAN NORMAL CONFIDENCE. DUE TO HIGH MODEL SPREAD, TODAY’S MANUAL 500-HPA HEIGHT BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEAN SOLUTIONS.  

TROUGHING AND BELOW NORMAL HEIGHTS LEAD TO ENHANCED PROBABILITIES OF BELOW NORMAL TEMPERATURES ACROSS THE WESTERN CONUS, PARTICULARLY EARLY IN THE PERIOD. ABOVE NORMAL HEIGHTS ASSOCIATED WITH THE RIDGE OVER EASTERN CANADA FAVOR ABOVE NORMAL TEMPERATURES FOR THE GREAT LAKES AND NORTHEAST. THERE ARE ENHANCED PROBABILITIES OF BELOW NORMAL TEMPERATURES FOR PARTS OF THE SOUTHEAST AND MID-ATLANTIC DUE TO BELOW NORMAL HEIGHTS AND ANOMALOUS NORTHERLY 500-HPA FLOW. RIDGING AND ABOVE NORMAL SSTS LEAD TO FAVORED ABOVE NORMAL TEMPERATURES ACROSS MUCH OF THE ALEUTIANS AND WESTERN MAINLAND ALASKA. WEAK TROUGHING DOWNSTREAM  FAVORS BELOW NORMAL TEMPERATURES FOR PARTS OF SOUTHEASTERN MAINLAND ALASKA AND THE PANHANDLE.   

AS A TROUGH PROGRESSES FROM WEST TO EAST ACROSS THE CONUS, ABOVE NORMAL PRECIPITATION IS FAVORED FOR MUCH OF THE EAST-CENTRAL CONUS. WEAK RIDGING LEADS TO SLIGHTLY ENHANCED PROBABILITIES OF BELOW NORMAL PRECIPITATION FOR PARTS OF THE SOUTHWESTERN AND NORTHWESTERN CONUS. MOIST FLOW AHEAD OF A TROUGH IN THE EASTERN PACIFIC LEADS TO ENHANCED PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR MUCH OF CALIFORNIA. CONVERSELY, NEAR TO BELOW NORMAL PRECIPITATION IS FAVORED FOR THE EASTERN SEABOARD UNDERNEATH ANOMALOUS NORTHERLY MID-LEVEL FLOW. ENHANCED WESTERLY 500-HPA FLOW LEADS TO INCREASED PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR WESTERN MAINLAND ALASKA AND THE ALEUTIANS. OFFSHORE FLOW IS ANTICIPATED FOR THE ALASKA PANHANDLE, FAVORING BELOW NORMAL PRECIPITATION  THERE. 

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO HIGHER THAN NORMAL SPREAD OVER MUCH OF THE FORECAST DOMAIN.  

8-14 DAY OUTLOOK FOR MAR 06 – 12 2018   

DURING THE WEEK-2 PERIOD POSITIVE 500-HPA HEIGHT ANOMALIES CONTINUE OVER MUCH  OF THE HIGH LATITUDES DUE TO RIDGES SOUTH OF THE ALEUTIANS AND OVER EASTERN  CANADA. HOWEVER, THE RIDGE OVER EASTERN CANADA IS FORECAST TO WEAKEN RELATIVE TO THE PRECEDING 6 TO 10 DAY PERIOD. BETWEEN THESE TWO FEATURES, HEIGHTS ARE EXPECTED TO LOWER OVER MAINLAND ALASKA IN ASSOCIATION WITH A DEVELOPING TROUGH. FARTHER TO THE SOUTH, NEAR TO BELOW NORMAL HEIGHTS ARE DEPICTED OVER MOST OF THE CONUS. GENERALLY, CYCLONIC FLOW IS EXPECTED OVER THE EASTERN CONUS WHILE WEAK RIDGING IS FORECAST OVER PARTS OF THE WESTERN CONUS. MODERATE TO HIGH SPREAD CONTINUES OVER MUCH OF THE FORECAST DOMAIN. THE ENSEMBLE MEAN SOLUTIONS FORM THE BASIS FOR THE WEEK-2 500-HPA BLEND DUE, IN PART, TO LARGE DISAGREEMENTS AMONG THE DETERMINISTIC MODELS.

BELOW NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE CONUS UNDERNEATH NEAR TO BELOW NORMAL HEIGHTS. HOWEVER, ABOVE NORMAL TEMPERATURES ARE SLIGHTLY FAVORED FOR PARTS OF THE NORTHEASTERN CONUS IN ASSOCIATION WITH THE RIDGE OVER EASTERN CANADA. NEAR TO ABOVE NORMAL HEIGHTS LEAD TO SLIGHTLY ELEVATED CHANCES FOR ABOVE NORMAL TEMPERATURES FOR PARTS OF THE SOUTHWEST. TROUGH DEVELOPMENT OVER MAINLAND ALASKA LEADS TO ENHANCED PROBABILITIES OF BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE STATE. HOWEVER, ABOVE NORMAL SSTS AND BELOW NORMAL SEA ICE EXTENT FAVOR ABOVE NORMAL TEMPERATURES FOR THE ALEUTIANS AND PARTS OF WESTERN MAINLAND ALASKA.   

THERE ARE LARGE DISAGREEMENTS AMONG RAW AND CALIBRATED DYNAMICAL MODEL  PRECIPITATION GUIDANCE LEADING TO LOWER THAN NORMAL CONFIDENCE. THERE ARE SLIGHTLY ENHANCED PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR PARTS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST CONUS DUE, IN PART, TO TELECONNECTIONS FROM THE EXPECTED POSITIVE HEIGHT ANOMALY CENTER OVER EASTERN CANADA. CALIBRATED DYNAMICAL MODEL GUIDANCE, AS WELL AS ANALOGS FROM THE MANUAL BLEND  FAVOR BELOW NORMAL PRECIPITATION FOR PARTS OF THE GREAT LAKES EXTENDING NORTHEAST TO PARTS OF NORTHERN NEW ENGLAND. WEAK RIDGING SLIGHTLY FAVORS BELOW NORMAL PRECIPITATION ACROSS THE WEST-CENTRAL CONUS. THERE ARE ENHANCED PROBABILITIES FOR ABOVE NORMAL PRECIPITATION FOR THE WEST COAST OF THE CONUS AHEAD OF A TROUGH OVER THE EASTERN PACIFIC. ENHANCED WESTERLY 500-HPA FLOW LEADS TO INCREASED PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR MUCH OF WESTERN ALASKA.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO FAIRLY HIGH MODEL SPREAD AND POOR AGREEMENT AMONG THE PRECIPITATION TOOLS. 

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON MARCH 15.

Week 3-4 Forecast Discussion Valid Sat Mar 10 2018-Fri Mar 23 2018

The Madden Julian Oscillation has been active for the last few weeks with convection propagating across the tropical Pacific into the Western Hemisphere. La Nina conditions continue, but a transition to ENSO neutral conditions is predicted during the boreal spring. The week 3-4 outlook relies primarily on dynamical model forecasts from the ECMWF, CFS and JMA ensembles, with additional input from a statistical regression model derived from the current state of ENSO and the MJO, as well as the contribution of decadal trends. Individual models and the multi-model ensemble (MME) from the Subseasonal Experiment (SubX), a suite of non-operational ensemble prediction systems, was also consulted.

Dynamical models for the week 3-4 period predict a changing circulation pattern from the week 2 through week 3-4 period. Models predict persistent above normal 500-hPa heights near the western Aleutian Islands for weeks 2, 3 and 4. During week 2 and week 3, models predict an amplification of negative 500-hPa height anomalies from southeastern Alaska into the North Pacific, near the Pacific Northwest of the CONUS. By week 4, most models predict a change to the circulation pattern with rising heights over the southern and eastern CONUS. Calibrated temperature probabilities from the ECMWF, CFS and JMA indicate increased probabilities of below normal temperatures for the northwestern CONUS, as well as much of Alaska, in the week 3-4 period, under predicted negative 500-hPa height anomalies. Anomalously low sea ice in the Bering Sea and strong positive temperature trends for the North Slope decrease the probabilities of below normal temperatures leading to a forecast of equal chances. Operational models also consistently indicate increased probabilities for above normal temperatures for parts of the Southwest, southern Texas and the Gulf Coast, as well as for eastern regions of the Northern Plains across the Great Lakes region into the Northeast. These dynamical model temperature forecasts for the CONUS are consistent overall with the combined impacts of MJO, ENSO and decadal trends, as indicated by the statistical multivariate regression forecast.

The week 3-4 outlook indicates increased probabilities of above median precipitation for the Pacific coast of central and northern California, Oregon, and Washington, as well as the southern Alaska Panhandle, ahead of negative 500-hPa height anomalies, as indicated by the SubX MME. Above median precipitation is also indicated for the North Slope of Alaska, as in the ECMWF forecast and decadal trends. Below median precipitation is most likely for southwestern regions of Alaska, ahead of a predicted ridge over the Aleutians. The probabilities of below median precipitation are also increased for the Southern Plains states and the Northeast CONUS, as indicated by operational ensemble prediction systems from ECMWF, CFS and JMA, as well as the models of the SubX MME. Above median precipitation is most likely for much of Florida, as indicated by the SubX MME mean and consistent with regressions based on the current MJO phase.

Sea surface temperatures are slightly below normal to the northwest of Hawaii and above normal near southeastern islands, resulting in a forecast of equal chances for most of the islands and a forecast of more likely above normal temperatures for Hilo and the big island of Hawaii. All dynamical models are consistent in predicting greater probabilities of above median precipitation across the Hawaiian Islands.

Some Indices of Possible Interest:

MJO

NCEP-NEFS	CFSv2

Analogs to the Outlook.

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

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

* Some concern due to the uniformity of the pattern that this is a computer error. I may redo tomorrow if the report is very different. [ after reviewing the new analogs today Tuesday February 27] I am sure that half are not correct so I can not fix the above but suggest you ignore the five Feb 5 Analogs as possibly one is correct]

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

The spread among the analogs from February 5 to March 12 is 35 days* which is fairly wide. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, is about February 22. These analogs are centered on 3 days and 4 days ago (February 22 or February 23). So the analogs could again be considered to be in sync with respect to weather that is we are likely to be getting weather that is similar to some extent to what we would expect to normally be getting now*. That  is not surprising given the projected cold air intrusion. 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.

Assuming the reported analogs are valid, including the duplicates, there are three Neutral Analogs, two La Nina analogs and five El Nino Analogs. The phases of the analogs this week strongly correlate with McCabe condition D and also with McCabe B. McCabe B and D are in some ways opposites. They both are associated with PDO Negative but McCabe B is associated with AMO Negative (while in reality it is Positive) and McCabe D (which is related to the Analogs for which I have less than full confidence) is associated with AMO Positive. McCabe D is the extreme Southwest Drought Scenario but both are associated with Great Lakes Drought. To some extent they both are roughly consistent with the NOAA 6 – 10 Day and 8 – 14 Day Forecasts so this makes me a bit more confident in the NOAA 6 – 14 Day Forecast than NOAA is.[Correction note made February 27, 2018: I am now certain that five of the Feb 5 for five successive years Analogs in the February 26, 2018 6 – 14 Day NOAA Report are a computer error by NOAA and possibly one is correct with four duplicates that are not valid. That suggests that McCabe B is probably more correct than McCabe B and D. It is probably best to ignore this part of my report as the raw data most likely is not reliable i.e. it looks like I have five or six good data points out of the ten. It may be that my analysis is still correct but missing four or five data points reduces my confidence in my analysis]

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  February 17, 2018	And the 30 Days ending February 24, 2018
A break in the drought for a small part of Arizona and NM and the warm anomaly spread to the East. A fairly major change.	Smaller coverage of the Southwest drought. The temperature anomaly pattern is not much changed.
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.

Reference Forecasts Full Month and Three Months.

Below are the Temperature followed by the Precipitation Outlooks for the month and three months shown in the Legend. These 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 into late February/Early March 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. It is further north than usual right now for this time of the year.

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

This graphic is anomalies i.e. deviations from normal not the actual temperatures.	This graphic is actuals not anomalies as is the case in the temperature map.
Notice that below the map there is a tabulation of magnitude of the current anomalies by region. The Arctic is very warm having shipped their cold air to Canada and CONUS. Eastern Asia is cool. So is Western Europe	We again see the dry belt stretching from Northern Africa to Eastern Asia but not including Southeast Asia. Mexico is very dry.

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. Western CONUS looks fairly wet, Eastern Australia is dry. 

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	It now looks fairly similar to the three-month average except that the western part of the cool anomaly no longer exists. .

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
Neutral	Cool along coast of Asia	Warm off of Anadyr Coast Warm off of Baja	Warm off East Coast Warm Northern Gulf of Mexico	Fairly Neutral but warm north of Scandinavia.
Equator	The La Nina cold tongue is fading.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cool west of North Africa Cool southeast of Africa south of Madagascar	cool	Warm southeast all the way to and beyond New Zealand	Cool but now mostly offshore Cool off of 30S but mostly offshore Warm anomaly way offshore at 40S.	Warm off 40S

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
Mediterranean and Black Sea neutral.  Caspian Sea cooling	Slight cooling off of Asia	Warming in Bering Sea Slight cooling west of CONUS Northwest Warming east of Dateline at Midlatitudes The changes are definitely in the direction of a more negative PDO. .	Warming off East Coast	Cooling south of Greenland and British Isles and west of North Africa.  .
Equator	Eastern Pacific warming to the east but cooling further west resembling a Modoki Pattern.  Cooling near the Maritime Continent. Warming east of Africa and Cooling west of Africa.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cooling off North Africa and Gulf of Guinea Warming west of Angola Warming off of a large part of East Africa to and beyond Madagascar Cooling Southwest of Africa.	Cooling	Cooling Northwest Cooling south and more extreme to the southeast and beyond New Zealand	Neutral except west of Ecuador as previously mentioned	Cooling off entire Northeast Cooling off 20S Cooling off 50S

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

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

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 February 26 in the afternoon working from the February 25 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 -0.8 which is a La Nina value. NOAA has reported the weekly Nino 3.4 to be slightly cooler at -1.1 which is a relatively strong La Nina value and we believe it is too high. Nino 4 is reported a little warmer this week at -0.2. Nino 3 is a little warmer at -0.9. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported much warmer at -0.0. I  understand that CDAS reports this Index to be considerable warmer than 0. It was up there close to 3 at one time so this index has been declining quite a bit and also fluctuating quite a bit which is not surprising as it is the area most impacted by the Upwelling off the coast. So it is an indication of the interaction between surface water and rising cool water. Thus it is subject to larger changes. I am only showing the currently issued version of the NINO SST Index Table as the prior values are shown in the small graphics on the right with this graphic. The same data in 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.

This is probably the best place to AGAIN express the thought that this way of measuring an ENSO event leaves a lot to be desired. Only the surface interacts with the atmosphere and is able to influence weather. The subsurface tells us how long the surface will remain cool (or warm). Anomalies are deviations from “Normal”. NOAA calculates and determines what is “Normal” which changes due to long ocean cycles and Global Warming. So to some extent, the system is “rigged”. Hopefully it is rigged to assist in providing improved weather forecasts. But to assume that any numbers reported can be assumed to be accurate to a high level of precision is foolhardy.

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

The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2016. The anomaly had returned to zero then reversed for a month but has again returned to zero and I expect positive values soon. In retrospect it was the Kelvin Wave 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.

The Kelvin Wave that would have put a quick end to this La Nina has faded and then we had and an upwelling wave. And now we have another looking more significant Kelvin Wave. This explains the gyrations in the forecast models first adding a month to the life of the La Nina and then recently removing that month and next time the models run the La Nina will be shown to be in its death throes. It almost looks like an El Nino is coming.

 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.

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

There is cold water from 170W to Land. At the west end of the cool anomaly it is not consistently even 100 meters deep (it was once over 200 meters deep). But we see some new cool anomalies at depth so it is hard to know what to make of that but they also now seem to be moving towards the surface.  We now have warm water developing west of the Dateline and crossing the Dateline at depth but no longer extending all the way to 120W and beyond but now to 160W which is more than 20 degrees further east than just a few weeks ago. La Nina’s days are numbered and the transition is happening differently that I thought it would but it is clearly happening and the pace is quickening.

The 28C Isotherm is at 165E, the 27C Isotherm is at 175E, the 25C Isotherm is now at 150W and the 20C Isotherm no longer is reaching the surface. It has been fairly stable for a number of weeks but the Indo-Pacific Warm Pool is gradually moving East and the Eastern Pacific Cool Pool is gradually being forced deeper..

The flattening of the Isotherm Pattern is an indication of ENSO Neutral just as the steepening of the pattern indicates La Nina or El Nino depending on where the slope shows the warm or cool pool to be. That flattening has occurred and we have gone to a Weak La Nina thermocline.

Tracking the change.

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 tells 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.

And now we have a recent update. It is quite dramatic.

This is the discussion

IRI Technical ENSO Update Published: February 19, 2018

Note: The SST anomalies cited below refer to the OISSTv2 SST data set, and not ERSSTv4. OISSTv2 is often used for real-time analysis and model initialization, while ERSSTv4 is used for retrospective official ENSO diagnosis because it is more homogeneous over time, allowing for more accurate comparisons among ENSO events that are years apart. During ENSO events, OISSTv2 often shows stronger anomalies than ERSSTv4, and during very strong events the two datasets may differ by as much as 0.5 C. Additionally, the ERSSTv4 may tend to be cooler than OISSTv2, because ERSSTv4 is expressed relative to a base period that is updated every 5 years, while the base period of OISSTv2 is updated every 10 years and so, half of the time, is based on a slightly older period and does not account as much for the slow warming trend in the tropical Pacific SST.

Recent and Current Conditions

In mid-February 2018, the NINO3.4 SST anomaly was in the upper portion of the weak La Niña range. For January the SST anomaly was -0.75 C, indicating weak La Niña, and for November-January it was -0.79 C, also in that range. The IRI’s definition of El Niño, like NOAA/Climate Prediction Center’s, requires that the SST anomaly in the Nino3.4 region (5S-5N; 170W-120W) exceed 0.5 C. Similarly, for La Niña, the anomaly must be -0.5 C or less. The climatological probabilities for La Niña, neutral, and El Niño conditions vary seasonally, and are shown in a table at the bottom of this page for each 3-month season. The most recent weekly anomaly in the Nino3.4 region was -0.9, showing weak La Niña but not far from the borderline of moderate La Niña. The pertinent atmospheric variables, including the lower level zonal wind anomalies, the Southern Oscillation Index and the anomalies of outgoing longwave radiation (convection), have been showing patterns suggestive of La Niña, although the Southern Oscillation has been weak and variable and the enhanced trade winds in the western Pacific have ceased. Subsurface temperature anomalies across the eastern equatorial Pacific, while recently weakening significantly, are also still mildly negative and not inconsistent with a La Niña nearing the end of its duration. Given the current and recent SST anomalies, the subsurface profile and the La Niña patterns in most key atmospheric variables, it appears we are in the later stage of a weak (but nearly moderate) La Niña.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued approximately one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it stated that the La Niña is likely to transition to ENSO-neutral during spring. A La Niña Advisory was once again issued with that Discussion. The latest set of model ENSO predictions, from mid-February, now available in the IRI/CPC ENSO prediction plume, is discussed below. Those predictions suggest that the SST is likely to remain in the weak La Niña range just for the February-April season, followed by a likely return to neutral starting with the March-May season.

As of mid-February, about 60% of the dynamical or statistical models predicts La Niña conditions for the initial Feb-Apr 2018 season, dropping to only around 25% for Mar-May and Apr-Jun. At lead times of 3 or more months into the future, statistical and dynamical models that incorporate information about the ocean’s observed subsurface thermal structure generally exhibit higher predictive skill than those that do not. For the May-Jul 2018 season, among models that do use subsurface temperature information, about 75% of models predicts neutral conditions and about 15% predicts La Niña conditions. For all models, starting with the second lead time of Mar-May 2018 and lasting through most of the forecast range, predictions for ENSO-neutral conditions have more than a 50% probability, with probabilities peaking around 75-80% for May-Jul. However, near the end of the forecast range, Sep-Nov and Oct-Dec, the probability for El Niño rises to over 40% and La Niña probabilities are only about 10%, leaving only about 45% for neutral.

Note  – Only models that produce a new ENSO prediction every month are included in the above statement.

Caution is advised in interpreting the distribution of model predictions as the actual probabilities. At longer leads, the skill of the models degrades, and skill uncertainty must be convolved with the uncertainties from initial conditions and differing model physics, leading to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution from that taken verbatim from the raw model predictions.

An alternative way to assess the probabilities of the three possible ENSO conditions is more quantitatively precise and less vulnerable to sampling errors than the categorical tallying method used above. This alternative method uses the mean of the predictions of all models on the plume, equally weighted, and constructs a standard error function centered on that mean. The standard error is Gaussian in shape, and has its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill results in a relatively narrower error distribution, while low skill results in an error distribution with width approaching that of the historical observed distribution. This method shows probabilities for La Niña at about 55% for Feb-Apr, dropping to near 35% for Mar-May, and decreasing thereafter to less than 20% for Apr-Jun through Oct-Dec. Probabilities for neutral conditions begin around 45% for Feb-Apr, rise to a peak around 80% for Apr-Jun, after which they drop to about 50% for Jul-Sep and to about 40% or less for Aug-Oct to Oct-Dec as El Niño probabilities rise, reaching nearly 50% by Oct-Dec. A plot of the probabilities generated from this most recent IRI/CPC ENSO prediction plume using the multi-model mean and the Gaussian standard error method summarizes the model consensus out to about 10 months into the future. The same cautions mentioned above for the distributional count of model predictions apply to this Gaussian standard error method of inferring probabilities, due to differing model biases and skills. In particular, this approach considers only the mean of the predictions, and not the total range across the models, nor the ensemble range within individual models.

In summary, the probabilities derived from the models on the IRI/CPC plume describe, on average, a slight preference for weak La Niña conditions for Feb-Apr 2018, followed by the period from Mar-May through Jun-Aug with neutral having more than a 50% chance. Chances for El Niño are small through May-Jul 2018, rising to near 35% for Jul-Sep and nearly 50% by the final period of Oct-Dec. A caution regarding this latest set of model-based ENSO plume predictions, is that factors such as known specific model biases and recent changes that the models may have missed will be taken into account in the next official outlook to be generated and issued early next month by CPC and IRI, which will include some human judgment in combination with the model guidance.

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 next week.

Forecasts from Other Meteorological Agencies.

Here is the JAMSTEC Model Forecast

And the recently released short discussion.

Feb. 19, 2018  Prediction from 1st Feb., 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 until summer. Then we expect evolution of a moderately positive Indian Ocean Dipole in fall. However, there is a large uncertainty in the prediction at present because of the large spread in the prediction plumes of the dipole mode index.

Atlantic Ocean forecast:

The Atlantic Niño and the Benguela Niño appear to develop in 2018. [Editor’s Note: We had noticed the strange temperature pattern along the Equator in the Atlantic and will research this further]

Regional forecast:

On a seasonal scale, most part of the Eurasian Continent will experience a warmer-than-normal condition except for western Europe. Northern/eastern U.S., southern Canada, central America, northern Brazil, Peru, Ecuador, Indochina, western, central and southern Africa, and northern Australia will experience a colder-than-normal condition in boreal spring.

As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for the Philippines, Indochina, central and southern Africa, Mexico, Ecuador, and northeastern Brazil during boreal spring, whereas most parts of Indonesia, southern China, Korea, East Africa, eastern U.S, and northern Brazil will experience a drier condition during boreal spring.

Most part of Japan will experience somewhat warmer-than-normal and drier-than-normal conditions in spring.

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

And the ENSO Outlook Discussion Issued on February 27, 2018: La Niña retreats

La Niña continues its decline, with sea surface temperatures in the central tropical Pacific Ocean warming over the past fortnight. Most models indicate a return to neutral conditions is likely early in the southern autumn.

The decline of this La Niña is evident in oceanic and atmospheric patterns, with several indicators recently returning to levels more consistent with a neutral ENSO phase. Sea surface temperatures are very close to neutral levels, cloudiness near the Date Line has increased, and trade winds are generally near normal across the equatorial Pacific. However, the current pulse of the Madden-Julian Oscillation (MJO) has been strong, and the effects of wind variations associated with it is likely to have amplified the decline. As the MJO progresses east, its effect will reverse, meaning some La Niña indicators are likely to strengthen briefly.

Four of eight international climate models surveyed by the Bureau maintain La Niña values through March. By May, only one model still exceeds La Niña thresholds. For July, all eight are within the neutral range. This ENSO event has had relatively little effect on Australian rainfall patterns over the 2017–18 summer.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole Outlook  Discussion Issued February 27, 2018

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 25 February was +0.20 °C. All six of the climate models surveyed by the Bureau indicate that the IOD will remain neutral into the southern hemisphere winter of 2018.

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

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 are coming 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 two or three more months. But the situation for next Summer is not yet totally clear.

Forecasting Beyond Five Years.

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

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

The odds of a climate shift for the Pacific taking place has significantly increased. It may be in progress. The AMO is pretty much neutral at this point (but more positive i.e. warm than I had expected) so it may need to become a bit more negative for the “McCabe A” pattern to become established. That seems to be slow to happen so I am thinking we need at least a couple more years for that to happen. 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

Planetary Wave Causes Freeze in California

Ohio River and Related Flooding and other Weather Impacts

200 Rivers at Flood Stage

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 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

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

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

History of ENSO Events as measured by the ONI

The new SON reading of -1.0 is the third La Nina Reading. These would have to extend through JFM 2018 for this to be recorded as a La Nina. The chances of this are about  60:40. These are three-month averages so DJF is pretty much determined since two months are in. The key will be March. Will March be sufficiently Neutral to have the three-month average be Neutral? 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.