February 19, 2018 Weather and Climate Report – Great Basin Blizzard

Written by Sig Silber

No need to get frightened. At any one point in time there are 3 to 7 Rossby Waves sometimes called Planetary Waves or Long Waves circling the Planet. They serve to equalize temperature between the Equator and the poles. The Long waves tend to produce a fairly predictable weather pattern. We will see how the current particular Rossby Wave, which is forecast to move slowly and even retrograde to the west in week two, might impact our weather for the next twenty-five days. The number of such waves at any point in time is called the Wave Number.

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Planetary Waves

This is a fairly good resource for more information and it has a similar diagram.

Great Basin

Map Source

Because this area is between two major mountain ranges it often serves as a conduit for troughs that drop down from the north and impact states along the way and in some cases Arizona and New Mexico. That is the current weather pattern in the West and is related to the Planetary Wave that is crossing Alaska and CONUS.  I am not going to provide detailed coverage of this blizzard because it, or at least the first wave within this pattern, will be over soon and local offices of the NWS are in a better position to do that. But it is the coldest storm so far this winter for the West. Some of the graphics in the article this evening will provide some coverage for this storm. There may be a follow-up storm later this week or even a third. We are not able to provide the hour by hour coverage that local offices of the NWS are able to do except when we run a special update which we do for major hurricanes etc. This is an important storm but does not rise to the level of justifying a special update report. It is mostly notable because it is February 19 and this is the first real winter storm of the winter for many states.

Let’s change topics.

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 not progressive. The pattern is rather static.
To the right is the week 3 and 4 Forecast. There is a warm anomaly in Northern Alaska and a large warm anomaly covering the Southern Tier of CONUS and a Northeast warm anomaly. There is a large cool anomaly in the Northwest that extends up into the Alaskan Panhandle and Southern Alaska.                      →			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left does not seem feasible with respect to the Southern Tier.

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) with the Western wet anomaly intensifying and the Eastern wet anomaly moderating.
To the right is the week 3 and 4 Experimental Forecast.    →                Northeast Alaska is wet and Southern Alaska, the Panhandle and a small area in the extreme Northwest is dry but south of that it is wet. The Northeast is dry.			↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left represents a very significant change.

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. 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 19, 2018, as I am looking at the above graphic, you see a continuation of the pattern of moisture entering the Northwest and via Mexico into Texas. The Moisture entering the Northwest is then partially traveling down the Great Basin rather than totally heading east.

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 1000 hPa. Further inland in Kamchatka there is High Pressure of at least 1024 hPa (the map ends there). The Aleutian Low is out of position to impact anything but Alaska. There remains a large and now better defined Low to the west of Hudson Bay with surface central pressure of 984 hPa. That Low actually extends all the way to the Atlantic Ocean. And very critical is the Pacific Subtropical High with surface central pressure of 1036 hPa. This High extends inland. The Bermuda High off the East Coast is also important with surface central pressure of 1024 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 just enough to allow troughs to form in the Great Basin. 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 interior to the Jet Stream.

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 19, 2018 was 4 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on February 19, 2018 was 4 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 19, 2018 was 4 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on February 19, 2018 was 4 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today February 19, 2018 and the Week 3/4 (assumption rich) discussion released Friday February 16, 2018

6-10 DAY OUTLOOK FOR FEB 25 – MAR 01, 2018  

TODAY’S ENSEMBLE MEAN SOLUTIONS ARE IN GOOD AGREEMENT ON THE EXPECTED 500-HPA FLOW PATTERN OVER THE FORECAST DOMAIN. A DEEP TROUGH IS FORECAST NORTHWEST OF HUDSON BAY EXTENDING EAST/SOUTHEAST OVER THE NORTH ATLANTIC, AND SOUTHWESTWARD OVER THE WESTERN CONUS. RIDGES ARE ANTICIPATED OVER THE GULF OF MEXICO AND WESTERN MAINLAND ALASKA. THE FLOW PATTERN IS PREDICTED TO BE RELATIVELY AMPLIFIED. THE ENSEMBLE SPAGHETTI DIAGRAMS INDICATE SMALL TO MODERATE SPREAD ACROSS THE MAJORITY OF THE FORECAST DOMAIN. TODAY’S MANUAL 500-HPA BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEANS FROM THE CANADIAN, EUROPEAN, AND GEFS MODEL SUITES. THE RESULTANT MANUAL BLEND DEPICTS NEAR TO ABOVE NORMAL HEIGHTS OVER MOST OF THE EASTERN CONUS, THE SOUTHERN PLAINS, THE ALEUTIANS, AND SOUTHWESTERN MAINLAND ALASKA, AND NEAR TO BELOW NORMAL HEIGHTS OVER MUCH OF THE WESTERN CONUS, THE NORTHERN PLAINS,  NORTHEASTERN MAINLAND ALASKA, AND THE ALASKA PANHANDLE.

PERSISTENT TROUGHING IN THE WESTERN CONUS LEADS TO INCREASED CHANCES FOR BELOW NORMAL TEMPERATURES FOR MUCH OF THE WESTERN AND NORTH-CENTRAL CONUS. A STRONG RIDGE FORECAST OVER THE SOUTHEASTERN U.S. LEADS TO ENHANCED CHANCES OF ABOVE NORMAL TEMPERATURES FOR THE EASTERN CONUS AND THE SOUTHERN PLAINS. ANOMALOUS  RIDGING OVER SOUTHWESTERN ALASKA FAVORS NEAR TO ABOVE NORMAL TEMPERATURES FOR MUCH OF WESTERN AND NORTHERN MAINLAND ALASKA AS WELL AS THE ALEUTIANS. ANOMALOUS NORTHERLY FLOW TILTS THE ODDS TO NEAR TO BELOW NORMAL TEMPERATURES FOR SOUTHEASTERN MAINLAND ALASKA AND THE ALASKA PANHANDLE.  

THE DEEP TROUGH FORECAST OVER THE WESTERN CONUS AND/OR ANOMALOUS SOUTHWESTERLY FLOW ENHANCE PROBABILITIES OF NEAR TO ABOVE NORMAL PRECIPITATION OVER PARTS OF THE SOUTHERN PLAINS, AND MOST OF THE EASTERN CONUS, EXCEPT FOR FLORIDA WHERE BELOW NORMAL PRECIPITATION IS INDICATED DUE TO THE HIGHLY ANOMALOUS SOUTHEAST RIDGE. BELOW NORMAL PRECIPITATION IS ALSO FAVORED FOR PARTS OF THE HIGH PLAINS, AND THE CENTRAL AND SOUTHERN ROCKIES, CONSISTENT WITH DYNAMICAL MODEL GUIDANCE FROM THE ECMWF ENSEMBLE MEAN SOLUTIONS. BELOW NORMAL HEIGHTS TILT THE ODDS TO NEAR TO ABOVE NORMAL PRECIPITATION FOR THE WESTERN CONUS. SURFACE LOW PRESSURE OVER THE EASTERN GULF OF ALASKA FAVORS ABOVE NORMAL PRECIPITATION FOR MUCH OF ALASKA.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE MODELS AND FORECAST TOOLS.  

8-14 DAY OUTLOOK FOR FEB 27 – MAR 05, 2018  

THE MEAN 500-HPA FLOW PATTERN EXPECTED FOR THE WEEK-2 PERIOD IS SIMILAR TO THAT DEPICTED FOR THE 6 TO 10 DAY TIME FRAME, ALTHOUGH SLIGHTLY LESS AMPLIFIED CIRCULATION FEATURES ARE INDICATED AND THE OVERALL LONG WAVE PATTERN IS SHIFTED A BIT WESTWARD. ABOVE NORMAL HEIGHTS ARE EXPECTED OVER MOST OF THE EASTERN CONUS, MAINLAND ALASKA, AND THE ALEUTIANS, WHILE BELOW NORMAL HEIGHTS ARE ANTICIPATED OVER THE WESTERN CONUS, AND THE SOUTHERN ALASKA PANHANDLE. 

THE WEEK-2 TEMPERATURE PROBABILITY FORECAST IS VERY SIMILAR TO THE 6-10 DAY FORECAST, EXCEPT SLIGHTLY LOWER PROBABILITIES DUE TO THE TYPICALLY INCREASED UNCERTAINTY IN THE WEEK-2 PERIOD, AND A GENERAL WESTWARD DISPLACEMENT OF THE TEMPERATURE ANOMALY PATTERN DUE TO AN EXPECTED RETROGRESSION OF THE OVERALL LONG WAVE HEIGHT PATTERN. 

THE BROAD TROUGH FORECAST OVER THE WESTERN CONUS ENHANCES PROBABILITIES OF NEAR TO ABOVE NORMAL PRECIPITATION OVER PARTS OF THE HIGH PLAINS AND MISSISSIPPI VALLEY AREA. ABOVE NORMAL HEIGHTS TILT THE ODDS TO NEAR TO BELOW NORMAL PRECIPITATION FOR PARTS OF THE EASTERN GREAT LAKES, THE OHIO VALLEY, THE MIDDLE ATLANTIC, THE NORTHEAST, AND FLORIDA. BELOW NORMAL PRECIPITATION IS ALSO FAVORED FOR COLORADO, CONSISTENT WITH DYNAMICAL MODEL GUIDANCE FROM THE ECMWF ENSEMBLE MEAN SOLUTIONS. BELOW NORMAL HEIGHTS TILT THE ODDS TO NEAR TO ABOVE NORMAL PRECIPITATION FOR PARTS OF THE UTAH, ARIZONA, NEVADA, AND CALIFORNIA. SURFACE LOW PRESSURE OVER THE EASTERN GULF OF ALASKA FAVORS ABOVE NORMAL PRECIPITATION FOR MUCH OF ALASKA.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE MODELS AND FORECAST 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 03 2018-Fri Mar 16 2018

This week’s outlook is influenced mostly by the La Nina base state and its extratropical response through the Pacific/North American pattern (PNA), which is negative and forecast by the GEFS to remain negative. The Madden Julian Oscillation (MJO), which was the dominant convective pattern over the Pacific during the past month, has weakened substantially over the past few days and is forecast to continue to weaken. Also, the GEFS forecasts both the Arctic and North Atlantic oscillations to trend negative over the next week, but this guidance was inconsistent over the past few days and isn’t used in this forecast. This leaves La Nina and its PNA-like response as the primary drivers for Weeks 3-4.

The dynamical models are in generally good agreement about the placement of a wave train that originates from the Central Pacific, associated with the negative PNA pattern. The main differences between the models are largely in the orientation and magnitude of a positive height anomaly over the Aleutians and a negative height anomaly to its south. There’s less agreement at the surface where the CFS extends cold in the Northwest quite far south through most of Texas, and east through much of the Ohio Valley. In contrast, the ECMWF keeps the cold in the Pacific Northwest and extends it east to the Northern Plains. This week’s outlook favors the ECMWF forecast because of its continuity with the Week-2 forecasts. The CFS and ECMWF models are in good agreement about warmth along the southern extent of the CONUS, which also agrees with historical trends expected from a La Nina base state. All of our dynamical guidance is in agreement on warmth throughout the Northeast. The temperature forecast for Alaska is also consistent with the La Nina base state.

All of our dynamical guidance agreed on below median precipitation throughout the Northeast CONUS and the Alaskan Panhandle, and on above median precipitation over the Northern California/Oregon/Northern Nevada regions. These regions also coincide broadly with the upper-level height pattern driven by a negative PNA. The CFS forecasts above median precipitation over the Gulf Coast, but the signal in the ECMWF is significantly weaker and covers a smaller area than in the CFS. The JMA model is even more different showing anomalous dryness over much of the same area. Given the differences between the three models and the lack of a strong La Nina precipitation signal in that area, we’ve opted to forecast equal chances.

Sea surface temperatures around Hawaii are slightly below normal, but model guidance suggests near-normal temperatures over the islands, resulting in a forecast of equal chances. However, the models which are in good agreement about slightly enhanced rainfall over the islands, have been reflected in the precipitation forecast.

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.

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

The spread among the analogs from January 30 to February 24 is 25 days which is a bit less tight than last week. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, is about February 12. These analogs are centered on 3 days and 4 days ago (February 15 or February 16). So the analogs could again be considered to be slightly out of 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 three or four days ago. 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.

Including the duplicates, there are two Neutral Analogs, five La Nina analogs and three El Nino Analogs. The phases of the analogs this week strongly correlate with McCabe condition B. McCabe B is associated with AMO (Negative while in reality it is Positive) and McCabe B is a relatively wet scenario but more so for the West and less so for the East. To some extent it is roughly consistent with the NOAA 6 – 10 Day and 8 – 14 Day Forecasts. But the association with periods of time when the AMO was Negative makes me less confident than NOAA in their 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  February 10, 2018	And the 30 Days ending February 17, 2018
Dry anomaly more intense but wetter to the north. The Warm Anomaly has switched to a cool anomaly in the West North Central region.	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.
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

Related to the dry conditions is the official Drought Monitor. If is issued every Thursday reflecting the conditions as agreed on as of the preceding Tuesday. I participate once a month in the discussion related to the situation in New Mexico. 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. The situation right now is fairly serious as it impacts cattle forage, dust, fire hazard among other things. It is likely to get worse before it gets better. Here are two useful links. First this one to the Drought Monitor Site and this to the NOAA Site that has additional information.

Reference Forecasts Full Month and Three Months.

Below are the Temperature followed by the Precipitation Outlooks for the month and three months shown in the Legend. These map are issued on the Third Thursday of the Month. The maps for the following month (but not the three-month maps) are updated on the last day of the month. The 6 – 10 day and 8 – 14 Day update daily and the Week 3/4 Map Updates every Friday so usually these are more up to date. Also the three shorter-term maps will generally cover a slightly different time period since they update daily as the month progresses. But these reference maps are sometimes useful if one wants to understand how the current month was originally forecast to play out.

	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 and should be returning to the set of positions shown below for July. 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	Cooling off of Asia except further north. Warming around and east of Kamchatka	Warming in Bering Sea and south of western Aleutians Slight cooling from the Equator to Baja The changes are definitely in the direction of a more negative PDO. .	Warming off East Coast Warming in the Gulf of Mexico	Cooling south of Greenland and British Isles and west of North Africa.  .
Equator	Eastern Pacific warming to the east but cooling further west.  Cooling near the Maritime Continent. Cooling east of South America
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cooling off North Africa Warming west of Angola Warming between Mozambique and Madagascar Cooling south and Southeast of Africa.	Slight cooling	Cooling North and East Warming Southeast and east of New Zealand	Warming offshore of 20S Cooling offshore of 30S	Cooling off entire Northeast Cooling off 20S down to Cape Horn

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 19 in the afternoon working from the February 18 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 -0.7 which is a La Nina value. NOAA has reported the weekly Nino 3.4 to be slightly cooler at -1.0 which is a moderate La Nina value and we believe it is too high. Nino 4 is reported a little cooler this week at -0.4. Nino 3 is a little warmer at -1.1. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported a bit warmer at -0.6. 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. I was planning to try to graph the slope of the decline to make a prediction as to when it reaches -0.5C.  The best laid plans oft go astray. The temperature anomaly has reversed and is colder. It explains why the models have added a month or half month to when the La Nina will be gone. The CDAS graphic which we also show is another way to do the same thing as is the BOM SOI graphic. The weather may already be reflecting the transition but this La Nina is saying “not so fast”.

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 we now have actually an upwelling wave. It is hard to assess it from the limited about of visual evidence here and it looks like it might be followed by another Kevin wave soon. Also notice there really is no cool water west of 100W meaning the La Nina is over even if not yet so reported. But we can see why the models added a half month or so to the expected duration of this La Nina.

 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 beyond the Dateline 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. 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. La Nina’s days are numbered but it looks like another month has been added to its life.

The 28C Isotherm is at 170E, the 27C Isotherm is at 175W, 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.

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. We have the opposite.	We see suppressed Outgoing Long Wave Radiation (OLR) at the Dateline i.e (dry) and we  see enhanced OLR at 120E ( wet)

And Now the Air Pressure to Confirm that the Atmosphere is Reacting to the Sea Surface Temperature Pattern. The most Common way to do that is to use an Index called the SOI.

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

Current SOI Readings

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 a 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 13, 2018:

La Niña decline may be hastened by recent shift in trade winds

The La Niña in the Pacific Ocean continues to decline. Sea surface temperatures in the central tropical Pacific have warmed steadily since late December, with most models forecasting La Niña will end early in the southern hemisphere autumn.

El Niño–Southern Oscillation (ENSO) indicators continue to show at least some La Niña characteristics. Sea surface temperatures indicate a weak La Niña pattern, with the coolest waters concentrated in the eastern Pacific Ocean, while the Southern Oscillation Index is neutral, but weakly positive. However, a very strong pulse of the  Madden-Julian Oscillation (MJO), which drove a burst of monsoonal activity over northern Australia in late January, has caused the western Pacific trade winds to weaken considerably. The rapid weakening of the trade winds may hasten the decline of La Niña. The MJO also led to above-average cloudiness at the Date Line for the first time since early September 2017.

In order for 2017–18 to be classed as a La Niña year, thresholds need to be exceeded for at least three months. Four of the eight climate models surveyed by the Bureau suggest this event is likely to last at least until late summer, while a few continue the event into the southern hemisphere autumn of 2018.

Typically, the strength of a La Niña event reflects the strength of its impact upon Australian climate. The current event is weak, and hence climate patterns have been significantly different from those observed in the last strong La Nina of 2010–12.  Large parts of eastern Australia have been drier than average for the past two or three months, the opposite of what is typically expected during La Niña.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole Outlook  Discussion Issued February 13, 2018

The Indian Ocean Dipole (IOD) is currently neutral. IOD events are unable to form between December and April.

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 11 February was −0.08 °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 are here for this Winter and Spring with La Nina Conditions already in place. But the situation for next Summer is not yet clear. However, we are getting very close to being able to forecast the end of this La Nina event. But it may only be a temporary end for the Summer and next Fall as it may return for next Winter or Spring. But that is now looking less likely with ENSO Neutral highly likely. There is no sign of the next El Nino.

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. On the other hand, AMO- is what is showing up in the pre-forecast analogs that NOAA provides and which I report on. That might mean something. So our assessment is that the standard time for Climate Shifts in the Pacific are likely to prevail and it most likely will be a gradual process with a speed up in less than five years but more than two years. The next El Nino may be the trigger.

E. Relevant Recent Articles and Reports

Weather in the News

Capetown Continues to Deal with Severe Drought.

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

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.