Written by Sig Silber
It just happens that the last day of April is on a Monday so we are running a BOGO special: May Update and Regular Weekly Weather and Climate Report. We will see how that works. It is a bit of mix and match but I think it is easier to read a single consolidated report than two separate reports both of which are based on the same information supplied today by NOAA. Also in this report I will show why it is very unlikely that we will have an El Nino next winter. But the “Pre-Forecast” NOAA Analogs suggest that I may be incorrect about this. .
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Because it seems like Spring has arrived, I will not be showing the full set of snow maps until next Fall. But there is still snow in the Northwest so I am showing the six-hour foreecast which auto-updates so it is always current.
This graphic shows the way our weather pattern has changed recently
And as stated in the lede paragraph, an El Nino for next winter seems unlikely. Below is the reason.
A. Now we will begin with our regular approach and focus on Alaska and CONUS (all U.S.. except Hawaii). Then I will address the May Update released today.
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.
|This shows magnitude rather than probability of being higher or lower than Normal and shows the middle day of the five day period.||It is difficult to compare this with the other maps that show deviation from climatology as we expect the north to be cooler than the south. But it does seem to be consistent with the 6 – 10 day map. You can see the difference between North and South is now normal and not impacted by cold air intrusions from Canada.|
|Click to Enlarge|
Transitioning from the 6 to 10 day outlook on the left (also called Week One) to the 8 to 14 day outlook (Week Two) on the right →
The pattern is slightly progressive west to east.
To the right is the week 3 and 4 Forecast. →
There is a warm anomaly for Alaska. There is a warm anomaly for 2/3rds of CONUS only excluding the Far West and the North Tier west of Michigan..
← The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems feasible.
B. Now let us address the NOAA Update of the May, 2018 Forecast.
NOAA has, as usual, issued an update for the month following the last day of the prior month. This NOAA update was issued today Monday April 30, 2018. In this Update Report, we present the Updated NOAA Outlook for May and compare it to the NOAA “Early Outlook” for May issued on April 19, 2018 about ten days ago. Please note: all smaller graphics can be enlarged by clicking on them or right clicking and selecting the “view image) option.
First, I present a summary showing the prior and the new May forecast and the previously issued three-month forecast. Larger graphics follow but these smaller graphics can be enlarged.
|Prior Issued on April 19, 2018|
|Updated on April 30, 2018|
|Three Month Forecast Issued on April 19, 2018|
Prior May Temperature Forecast Issued on April 19, 2018
New May Temperature Forecast Issued on April 30, 2018
Turning to Precipitation
Prior May Precipitation Forecast issued on April 19, 2018
New May Precipitation Forecast Issued on April 30, 2018
Here is the NOAA Discussion released on April 30, 2018 with the May Update. Because this is a few days after the Week 3 – 4 Release, we are assuming that todays discussion of the May Update incorporates or supersedes the key elements of the Week 3 – 4 discussion so we are not including that discussion in this section but it is presented later in this report.
30-DAY OUTLOOK DISCUSSION FOR MAY 2018
THE MAY 2018 FORECAST IS UPDATED TO ACCOUNT FOR THE LATEST MODEL GUIDANCE AND SHORT TERM WEATHER PHENOMENA THAT ARE LIKELY TO EXERT A STRONG INFLUENCE ON THE MONTHLY-AVERAGED CLIMATE. OUR MID-MONTH ASSESSMENT OF LOW-FREQUENCY CLIMATE VARIABILITY IS LARGELY UNCHANGED. THE MJO IS CURRENTLY WEAK, BUT COULD REORGANIZE OVER THE WESTERN HEMISPHERE DURING WEEK-2. WHILE THIS IS NOT EXPECTED TO YIELD A STRONG EXTRATROPICAL RESPONSE, THERE IS VERY MODEST EMPIRICAL EVIDENCE THAT THIS EVOLUTION COULD FAVOR A COOLING TREND, RELATIVE TO NORMAL, OVER PARTS OF THE PLAINS DURING THE MONTH.
THE TEMPERATURE FORECAST IS UPDATED TO REFLECT MAJOR WARMING TRENDS FORECAST OVER BOTH THE EASTERN AND WESTERN PARTS OF THE CONUS: THE FORMER DURING THE FIRST FIVE DAYS OF THE MONTH, THE LATTER DURING THE DAY 6-14 PERIOD. THE LATEST MODEL GUIDANCE FROM THE CFS AND OUR OFFICIAL WEEK-2 AND WEEK 3-4 FORECAST PRODUCTS ALL SUPPORT A GENERAL TILT TOWARD ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE CONUS. THE ODDS OF ABOVE-NORMAL TEMPERATURES ARE THE GREATEST OVER PARTS OF THE INTERIOR WEST, WHERE A MAJOR, PROLONGED WARMUP IS FORECAST FROM ABOUT MAY 6 ONWARD. A WEAKNESS IN PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES IS EVIDENT OVER PARTS OF THE PLAINS, MISSISSIPPI VALLEY, AND SOUTHEAST. PERIODIC UPPER-LEVEL TROUGHING IS INDICATED FOR THESE REGIONS, LIMITING FORECAST CONFIDENCE. ABOVE-NORMAL TEMPERATURES ARE ALSO FORECAST FOR ALASKA, WITH THE BEST ODDS ACROSS THE NORTH SLOPE, WHERE LONG-TERM WARMING TRENDS ARE DOMINANT.
THE PRECIPITATION FORECAST FIRST TAKES INTO ACCOUNT AREAS OF HEAVY RAINFALL FORECAST AT THE BEGINNING OF THE MONTH. THE HEAVIEST RAIN RELATIVE TO NORMAL IS FORECAST OVER TEXAS, WITH A SECONDARY REGION OVER THE CENTRAL PLAINS AND UPPER MIDWEST. THE MONTHLY-AVERAGED CIRCULATION OVER NORTH AMERICA IS EXPECTED TO FAVOR ENHANCED SOUTHERLY FLOW ACROSS MUCH OF THE CENTRAL CONUS, SO PRECIPITATION EVENTS ARE LIKELY TO OCCUR THROUGH THE MONTH. THE FIRST WEEK OF MAY IS FORECAST TO BE QUITE DRY OVER PARTS OF THE TENNESSEE VALLEY, SOUTHERN APPALACHIANS, AND THE SOUTHEAST. BEYOND WEEK-1, PRECIPITATION SIGNALS ARE WEAK OVER MUCH OF THE EASTERN CONUS, LEADING TO EXPANDED COVERAGE OF AN EQUAL CHANCES FORECAST FOR PARTS OF THE EASTERN SEABOARD. UPPER-LEVEL RIDGING IS FORECAST OVER THE NORTHWEST, LEADING TO A FORECAST FAVORING BELOW-AVERAGE PRECIPITATION. ANOMALOUS SOUTHERLY FLOW IS FORECAST OVER ALASKA, ESPECIALLY EARLY IN THE MONTH; THIS FAVORS ABOVE-NORMAL PRECIPITATION AT REASONABLY HIGH PROBABILITIES FOR THE SOUTHWESTERN PARTS OF THE STATE.
THE NEXT MONTHLY OUTLOOK…FOR JUN … WILL BE ISSUED ON THU MAY 17 2018
Visual Consistency Testing.
Sometimes it is useful to see how the Monthly forecast fits with the 1 – 5 Day, 6 – 10 Day , 8 – 14 Day and Week 3 and 4 forecasts. I do not have comparable maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing for temperature is the Day 3 Maximum Temperature and for precipitation the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week but showing absolute QPF (inches of precipitation) not QPF deviation from Normal.
|The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts? →|
← The full month forecast seems to fit with the concatenated partial month forecasts.
And then Precipitation
Sometimes it is useful to compare the forecast for the current month with the prior three-month forecast to see if the updated forecast for May might impact the prior forecast for May/June/July issued eleven days ago.
May 2018 Plus May – July 2018 Outlook
One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.
*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two and Three forecast that one derives must average out to the probabilities shown in the three-month maps.
For comparison purposes, here are the NOAA May-June-July forecast maps on the first set of rows and the June-July-August AMSTEC forecast maps for North America in the seond set of rows.
|NOAA May-June-July 2018 Temperature||NOAA May-June-July 2018 Precipitation|
|JAMSTEC June-July-August 2018 Temperature||JAMSTEC June-July-August 2018 Precipitation|
Let’s now return our focus back on Alaska and CONUS (all U.S.. except Hawaii).
This view of the past 24 hours provides a lot of insight as to what is happening.
You can see from this animation that most of the moisture entering CONUS is coming across the southern tier of CONUS or Mexico or entering from the Gulf of Mexico.
Tonight, Monday evening April 30, 2018, as I am looking at the above graphic, you see the continuation of that pattern with it seems a break in the action of moisture entering from the Pacific. The next storm is forecast to drop down from further north. . ..
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
Day One CONUS Forecast
|Day Two CONUS Forecast|
These graphics update and can be clicked on to enlarge but my brief comments are only applicable to what I see on Monday night prior to publishing.
60 Hour Forecast Animation
Here is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. Beyond 60 hours, additional maps are available at links provided below. The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color coding.
You can enlarge the below daily (days 3 – 7) weather maps for CONUS by clicking on Day 3 or Day 4 or Day 5 or Day 6 or Day 7. These maps auto-update so whenever you click on them they will be forecast maps for the number of days in the future shown. You can see the next East Coast Nor’easter.
What is Behind the Forecasts? Let us try to understand what NOAA is looking at when they issue these forecasts.
Below is a graphic which highlights the forecasted surface Highs and the Lows re air pressure on Day 7. The Day 3 forecast can be found here. the Day 6 Forecast can be found here. Actually all the small graphics below can be clicked on to enlarge them.
When I look at this Day 7 forecast, there is a Low over Kamchatka with surface central pressure of 1000 hPa. There is a another Low to the east in the Gulf of Alaska with two centroids with surface central pressure of 1008 hPa: one cetroid over the Eastern Aleutians and the other to the southwest. This week, the Hawaiian High with surface central pressure of 1024 hPa and extending very much onshore will play a decisive role in blocking storms after Day 7 from tracking down offshore of California but forcing them to stay north or travel down the Great Basin. Over the Southern Rockies there is a High with surface central pressure of 1020hPa which may be the leading edge of the Hawaiian High.
The Northeast has a Low with surface central pressure of 996 hPa and the Southeast has a High 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.
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.
We do not see a consistent pattern for the Jet Stream right now. That is probably seasonal.
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. Of interest is the Pacific Coast Storm which looks like it will not make it very far south.
|Day 3 Above, 6 Below||Day 4 Above,7 Below||Day 5 Above.|
Here is the seven-day cumulative precipitation forecast. More information is available here.
Four – Week Outlook: Looking Beyond Days 1 to 5, What is the Forecast for the Following Three + Weeks?
I use “EC” in my discussions although NOAA sometimes uses “EC” (Equal Chances) and sometimes uses “N” (Normal) to pretty much indicate the same thing although “N” may be more definitive.
First – Temperature
6 – 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on April 30, 2018 was 3 out of 5
8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on April 30, 2018 was 3 out of 5).
Looking further out.
Now – Precipitation
6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on April 30, 2018 was 3 out of 5)
8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on April 30, 2018 was 3 out of 5)
Looking further out.
Here is the 6 – 14 Day NOAA discussion released today April 30, 2018 and the Week 3/4 discussion released Friday April 27, 2018.
6-10 DAY OUTLOOK FOR MAY 06 – 10 2018
DURING THE 6-10 DAY PERIOD, TODAY’S ENSEMBLE MEAN SOLUTIONS DEPICT A 500-HPA TROUGH OVER EASTERN NORTH AMERICA AND A RIDGE OVER WESTERN CANADA AND EASTERN ALASKA. A WEAK TROUGH IS PREDICTED OVER THE SOUTHWESTERN COUNS. UPSTREAM, A THROUGH CONTINUES OVER THE BERING SEA EXTENDING SOUTHEASTWARD OVER THE EASTERN PACIFIC OCEAN. THE 500-HPA HEIGHT BLEND, BASED ON THE ENSEMBLE MEAN SOLUTIONS, DEPICTS ABOVE NORMAL HEIGHTS ACROSS MOST OF THE CONUS, AND EASTERN ALASKA.
ENHANCED PROBABILITIES OF BELOW NORMAL TEMPERATURES ARE INDICATED FOR MUCH OF THE NORTHEASTERN CONUS ASSOCIATED WITH THE TROUGH OVER THE EASTERN CONUS MOVING EASTWARD. INCREASED CHANCES OF ABOVE NORMAL TEMPERATURES ARE INDICATED OVER PARTS OF THE SOUTHEASTERN CONUS AHEAD THE TROUGH. ABOVE NORMAL TEMPERATURES ARE ALSO FAVORED FOR THE WESTERN CONUS EXTENDING TO THE HIGH PLAINS AS A RIDGE PERSISTS OVER THE REGION. ABOVE NORMAL TEMPERATURES ARE FAVORED FOR WESTERN AND NORTHERN ALASKA AHEAD OF A TROUGH OVER THE BERING SEA. BELOW NORMAL TEMPERATURES ARE FAVORED FOR PARTS OF SOUTHERN ALASKA RELATED TO ANTICIPATED CLOUDINESS AND PRECIPITATION. PERSISTENT RIDGING OVER EASTERN ALASKA LEADS TO INCREASED ODDS OF ABOVE NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE.
ABOVE NORMAL PRECIPITATION IS FAVORED FOR THE CENTRAL AND SOUTHERN HIGH PLAINS IN ASSOCIATION WITH A WEAK TROUGH OVER THE SOUTHWESTERN CONUS. THE TROUGH OVER THE EASTERN CONUS LEADS TO INCREASED ODDS OF ABOVE NORMAL PRECIPITATION FROM FLORIDA TO THE MIDDLE ATLANTIC COAST STATES. MEANWHILE, BELOW NORMAL PRECIPITATION IS FAVORED BEHIND THE TROUGH OVER MUCH OF THE REST OF THE EASTERN CONUS. BELOW NORMAL PRECIPITATION IS ALSO FAVORED FOR THE NORTHWESTERN CONUS EXTENDING TO PARTS OF THE NORTHERN PLAINS AS HEIGHTS RISE ACROSS THESE REGIONS. ABOVE NORMAL PRECIPITATION IS FAVORED FOR MUCH OF ALASKA AHEAD OF A TROUGH OVER THE BERING SEA.
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: NEAR AVERAGE, 3 OUT OF 5, DUE TO RELATIVELY GOOD OVERALL MODEL AGREEMENT OFFSET BY AN ANTICIPATED PATTERN CHANGE ACROSS MUCH OF THE FORECAST DOMAIN.
8-14 DAY OUTLOOK FOR MAY 08 – 14 2018
DURING WEEK-2, A MEAN LONGWAVE 500-HPA TROUGH IS PREDICTED OVER EASTERN NORTH AMERICA, WHILE A MEAN RIDGE IS EXPECTED OVER THE WESTERN CONUS EXTENDING TO EASTERN ALASKA. A MEAN TROUGH IS ANTICIPATED TO PERSIST UPSTREAM OVER THE BERING SEA EXTENDING TO THE GULF OF ALASKA. THE MANUAL 500-HPA HEIGHT BLEND IS BASED ON THE ENSEMBLE MEAN SOLUTIONS AND FEATURES ABOVE NORMAL HEIGHTS ACROSS MUCH OF THE CONUS AND EASTERN ALASKA. NEAR TO BELOW NORMAL HEIGHTS ARE ANTICIPATED FOR WESTERN ALASKA.
ABOVE NORMAL TEMPERATURES ARE FAVORED ACROSS THE WESTERN CONUS DUE TO RIDGING. A MEAN TROUGH OVER THE EASTERN CONUS LEADS TO INCREASED CHANCES OF BELOW NORMAL TEMPERATURES FOR THE GREAT LAKES REGION. NEAR TO ABOVE NORMAL TEMPERATURES ARE FAVORED FOR WESTERN AND NORTHERN ALASKA AHEAD OF A TROUGH OVER THE BERING SEA, WHILE BELOW NORMAL TEMPERATURES ARE FAVORED FOR SOUTHEASTERN MAINLAND ALASKA. ABOVE NORMAL TEMPERATURES ARE FAVORED FOR THE FLORIDA PENINSULA DUE TO AHEAD OF THE TROUGH OVER EASTERN NORTH AMERICA.
THERE ARE ENHANCED PROBABILITIES OF ABOVE NORMAL PRECIPITATION FOR THE CENTRAL HIGH PLAINS AND PARTS OF THE SOUTHEASTERN SEABOARD CONSISTENT WITH GEFS REFORECAST GUIDANCE. ENHANCED PROBABILITIES OF BELOW NORMAL PRECIPITATION ARE FAVORED FOR THE SOUTHERN PLAINS BEHIND THE TROUGH OVER EASTERN NORTH AMERICA. BELOW NORMAL PRECIPITATION IS ALSO FAVORED FOR PARTS OF THE MID-ATLANTIC AND NORTHEAST DUE TO ANTICIPATED MEAN SURFACE HIGH PRESSURE. RIDGING AND ABOVE NORMAL HEIGHTS ACROSS MUCH OF THE WESTERN AND NORTH-CENTRAL CONUS LEAD TO ENHANCED PROBABILITIES OF BELOW NORMAL PRECIPITATION FOR THESE REGIONS. NEAR TO ABOVE NORMAL PRECIPITATION IS FAVORED FOR ALASKA AHEAD OF A MEAN TROUGH OVER THE EASTERN BERING SEA.
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 3 OUT OF 5, DUE TO GOOD AGREEMENT ON THE OVERALL 500-HPA PATTERN, OFFSET BY INCONSISTENCIES WITH THE GEFS AND ECMWF BIAS CORRECTED REFORECAST TOOLS OVER THE EASTERN CONUS FOR BOTH TEMPERATURE AND PRECIPITATION.
THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON MAY 17.
Week 3-4 Forecast Discussion Valid Sat May 12 2018-Fri May 25 2018
The Northern Hemisphere circulation has started to spin down as meridional temperature gradients weaken during the transition to the warm season. This means that teleconnections have weakened, and will continue to weaken, during the Week 3/4 forecast period. Also, the tropics are quiet as La Nina continues to weaken and Nino 3.4 SST anomalies have crept up towards zero over the past few months. The MJO is inactive right now and there isn’t any trustworthy guidance that suggests it will strengthen appreciably within the next few weeks. This means that the forecast is based mostly on a blend of calibrated CFS and ECMWF model output.
Dynamical model guidance mostly agrees on moderate amplitude ridging over the eastern 2/3 of the CONUS during Week-3 and a less amplified pattern than Week-2. There is some uncertainty in how quickly the anomalous ridging will leave the eastern CONUS during Week-4; the CFS forecasts much weaker height anomalies during this period than the ECMWF. Even if the area of near zero height anomalies were to verify during Week-4, the eastern CONUS would probably still end up warmer than normal during the entire forecast period. Because of this we’ve forecast most of the eastern CONUS to experience above normal temperatures.
We have also forecast an area of enhanced 55% probabilities of above normal temperatures over the Southern and Central Plains. Since there’s a lack of dynamical forcing over the west in any of the models, we are forecasting equal chances of above and below normal temperatures over the West Coast and Northern Tier stretching from the Pacific Northwest to the Great Lakes. Model agreement is strong for above normal temperatures over Alaska, including an area of 55% probabilities over Northwestern Alaska, especially during Week-3.
Enhanced ridging over the eastern CONUS is expected to lead to a broad area of below normal precipitation during the forecast period, but the duration of the upper level ridge over the eastern CONUS is also a question here. While the calibrated dynamical guidance from the CFS, ECMWF, and JMA models all agree on this area of dryness, the JMA and some of the SubX models suggest that there could also be anomalous precipitation over the very central part of the country (northeast TX, OK, KS, MO, and IA). This is mostly because these models move the ridge out faster than the CFS and ECMWF and replace it with weak troughing. We’ve left the potential area of enhanced precipitation off of the map because it is low confidence, but it’s important to keep it in mind as a possible scenario.
We have forecast a 60% chance of above-normal temperatures and a 55% chance of above-normal precipitation over the Hawaiian Islands, which is supported by both the CFS and ECMWF models.
Some Indices of Possible Interest:
Madden Julian Oscillation (MJO)
Analogs to the Outlook.
Now let us take a detailed look at the “Analogs”.
NOAA normally provides two sets of Analogs.
A. Analogs related to the 5 day period centered on 3 days ago and the 7 day period centered on 4 days ago. “Analog” means that the weather pattern then resembles the recent weather pattern and the recent pattern is used to initialize the models to predict the 6 – 14 day Outlook.
B. There is a second set of analogs associated with the Outlook. It compares the forecast (rather than the prior period) to past weather patterns. I have not been regularly analyzing this second set of information. The first set applies to the 5 and 7 day observed pattern prior to today. The second set, relates to the correlation of the forecasted outlook 6 – 10 days out and 8 – 14 days out with similar patterns that have occurred in the past during a longer period that includes the dates covered by the 6 – 10 Day and 8 – 14 Day Outlook. The second set of analogs also has useful information as it indicates that the forecast is feasible in the sense that something like it has happened before. I am not very impressed with that approach. But in some ways both Approach A and B are somewhat similar. I conclude that if the Ocean Condition now are different then the analogs and if the state of ENSO now is different than the analogs that is a reason to have increased lack of confidence in the forecasts and vice versa.
They put the first set of analogs in the discussion with the second set available by a link so I am assuming that the first set of analogs is the most meaningful and I find it so. But NOAA prefers the first set (A) as it helps them (or at least they think it does) assess the quality of the forecast.
Here are today’s analogs in chronological order although this information is also available with the analog dates listed by the level of correlation. I find the chronological order easier for me to work with. The first set (A) which is what I am using today applies to the 5 and 7 day observed pattern prior to today.
|Apr 17, 1964 (2)||Neutral||–||N||Just after Modoki Type I|
|Apr 25, 1979||Neutral||+||–|
|May 10, 1992||El Nino||+||–||Modoki Type II|
|May 11, 1992||El Nino||+||–||Modoki Type II|
|Apr 17, 2002||Neutral||–||+(t)||Just before Modoki Type I|
|Apr 26, 2004||Neutral||+||+||Just Before Modoki Type II|
|Apr 15, 2008||Neutral||–||+||Before Modoki Type II|
|Apr 22, 2009 (2)||La Nina||–||–||Tail End|
(t) = a month where the Ocean Cycle Index has just changed or does change the following month.
The spread among the analogs from April 15 to May 11 is 26 days. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, and fairly accurate if the dates are reasonably evenly distributed, is about April 28. These analogs are centered on 3 days and 4 days ago (April 26 or April 27). So the analogs could be considered to be close to being in sync with respect to weather that we would normally be getting right now.
For more information on Analogs see discussion in the GEI Weather Page Glossary. For sure it is a rough measure as there are so many historical patterns but not enough to be a perfect match with current conditions. I use it mainly to see how our current conditions match against somewhat similar patterns and the ocean phases that prevailed during those prior patterns. If everything lines up I have my own measure of confidence in the NOAA forecast. Similar initial conditions should lead to similar weather. I am a mathematician so that is how I think about models.
Including duplicates, there are six Neutral Analogs, two La Nina analogs and two El Nino Analogs. The pre-forecast analogs this week do not favor any of the McCabe Conditions. The oceans’ low-frequency cycles also appear to be mixed. This mixture in a number of different dimensions casts doubt on the ability of the models to be very reliable right now.
The seminal work on the impact of the PDO and AMO on U.S. climate can be found here. Water Planners might usefully pay attention to the low-frequency cycles such as the AMO and the PDO as the media tends to focus on the current and short-term forecasts to the exclusion of what we can reasonably anticipate over multi-decadal periods of time. One of the major reasons that I write this weather and climate column is to encourage a more long-term and World view of weather.
|In color||Black and White same graphics|
|McCabe Condition||Main Characteristics|
|A||Very Little Drought. Southern Tier and Northern Tier from Dakotas East Wet. Some drought on East Coast.|
|B||More wet than dry but Great Plains and Northeast are dry.|
|C||Northern Tier and Mid-Atlantic Drought|
|D||Southwest Drought extending to the North and also the Great Lakes. This is the most drought-prone combination of Ocean Phases.|
You may have to squint but the drought probabilities are shown on the map and also indicated by the color coding with shades of red indicating higher than 25% of the years are drought years (25% or less of average precipitation for that area) and shades of blue indicating less than 25% of the years are drought years. Thus drought is defined as the condition that occurs 25% of the time and this ties in nicely with each of the four pairs of two phases of the AMO and PDO.
Historical Anomaly Analysis
When I see the same dates showing up often I find it interesting to consult this list.
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.
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. It is important since drought impacts the U.S. economy.
C. Beyond Alaska and CONUS Let’s Look at the World which of course also includes Alaska and CONUS
It is Useful to Understand the Semipermanent Pattern that Control our Weather and Consider how These Change from Winter to Summer. These two graphics (click on each one to enlarge) are from a much larger set available from the Weather Channel. They highlight the position of the Bermuda High which they are calling the Azores High in the January graphic and is often called NASH and it has a very big impact on CONUS Southeast weather and also the Southwest. You also see the north/south migration of the Pacific High which also has many names and which is extremely important for CONUS weather and it also shows the change of location of the ITCZ which I think is key to understanding the Indian Monsoon. A lot of things become much clearer when you understand these semi-permanent features some of which have cycles within the year, longer period cycles and may be impacted by Global Warming. We are now moving ito May and should be returning to the set of positions shown below for July (and that appears to be happening at least in the Pacific).For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant. Notice the Winter position of the Pacific High (Hawaiian High). It has been further north than usual for this time of the year. But it is forecast to drop down closer to its usual position
Forecast for Today (you can click on the maps to enlarge them)
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
|Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader.||The pattern is less Amplified.|
And now we have experimental forecasts from the U.S. NAEFS Model. They are difficult to read without first enlarging them.
|You can really see that Northern Africa is quite warm.||You have click on this to read it. There are a lot of extremes dry and wet shown.|
Looking Out a Few Months
Here is the precipitation forecast from Queensland Australia:
It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. But the current reading of the SOI is probably more impacted by the SOI than ENSO so its predictive value out three months is questionable.
One can always find the latest JAMSTEC maps by clicking this link. You will find additional maps that I do not general cover in my monthly Update Report. Remember if you leave this page to visit links provided in this article, you can return by hitting your “Back Arrow”, usually top left corner of your screen just to the left of the URL box.
Sea Surface Temperature (SST) Departures from Normal for this Time of the Year i.e. Anomalies
My focus here is sea surface temperature anomalies as they are one of the two largest factors determining weather around the World. If we want to have a good feel for future weather we need to look at the oceans as our weather mostly comes from oceans and we need to look at
- Surface temperature anomalies (weather develops from the ocean surface and
- The changes in the temperature anomalies since that may provide clues as to how the surface anomalies will change based on the current trend of changes. This is not that easy to do since the oceans are deep, there are many currents, winds have an impact etc. Two ways that are available to use are to look at the change in the situation today compared to the average over a period of time and NOAA also produces a graphic of monthly changes. I use both. The first set of graphics is simply looking at the average compared to today and that is below.
|Three Month Average Anomaly||Current Anomaly|
|La Nina shows up||The cool anomaly is displaced to the west a bit. We see a lot of white where we used to see blue.|
And when we look in more detail at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.
Then we look at the change in the anomalies. The SST anomaly is sort of like the first derivative and the change in the anomaly is somewhat like a second derivative. It tells us if the anomaly is becoming more or less intense.
Here it gets a little tricky as for this graphic red does not mean a warm anomaly but a warming of the anomaly which could mean more warm or less cool and blue does not mean cool but more cool or less warm.
|Mediterranean, Black Sea and Caspian Sea||Western North Pacific||West of North America||East of North America||North Atlantic|
Eastern Mediterranean warming
Warming around Japan
Cooling off Indochina
|Cooling southwest of Alaska|
Warming around British Isles
|Equator||Eastern Pacific consistently extreme warming to the east except in one spot at about 90W.|
|Africa||West of Australia||North, South and East of Australia||West of South America||East of South America|
|Warming west of Angola|
Warming east of Africa beyond Madagascar
Sleight cooling offshore of 40S
Warming east of 30S to 50S
This may be a good time to show the recent values to the indices most commonly used to describe the overall spacial pattern of temperatures in the (Northern Hemisphere) Pacific and the (Northern Hemisphere) Atlantic and the Dipole Pattern in the Indian Ocean. Notice the change in the PDO in July of 2017 and the stability of the AMO index.
|Most Recent Six Months of Index Values||PDO Click for full list|
AMO click for full list.
|Indian Ocean Dipole (Values read off graph)|
Switching gears, below is an analysis of projected tropical hazards and benefits over an approximately two-week period.
* Moderate Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend. ** High Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.
C. Progress of ENSO
A major driver of weather is Surface Ocean Temperatures. Evaporation only occurs from the Surface of Water. So we are very interested in the temperatures of water especially when these temperatures deviate from seasonal norms thus creating an anomaly. The geographical distribution of the anomalies is very important. To a substantial extent, the temperature anomalies along the Equator have disproportionate impact on weather so we study them intensely and that is what the ENSO (El Nino – Southern Oscillation) cycle is all about. Subsurface water can be thought of as the future surface temperatures. They may have only indirect impacts on current weather but they have major impacts on future weather by changing the temperature of the water surface. Winds and Convection (evaporation forming clouds) is weather and is a result of the Phases of ENSO and also a feedback loop that perpetuates the current Phase of ENSO or changes it. That is why we monitor winds and convection along or near the Equator especially the Equator in the Eastern Pacific.
Starting with Surface Conditions.
TAO/TRITON GRAPHIC (a good way of viewing data related to the part of the Equator and the waters close to the Equator in the Eastern Pacific where we monitor to determining the current phase of ENSO. It is probably not necessary in order to follow the discussion below, but here is a link to TAO/TRITON terminology.
And here is the current version of the TAO/TRITON Graphic. The top part shows the actual temperatures, the bottom part shows the anomalies i.e. the deviation from normal.
Location Bar for Nino 3.4 Area Above and Below
My Calculation of the Nino 3.4 Index
I calculate the current value of the Nino 3.4 Index each Monday using a method that I have devised. To refine my calculation, I have divided the 170W to 120W Nino 3.4 measuring area into five subregions (which I have designated from west to east as A through E) with a location bar shown under the TAO/TRITON Graphic). I use a rough estimation approach to integrate what I see below and record that in the table I have constructed. Then I take the average of the anomalies I estimated for each of the five subregions.
So as of Monday April 30, in the afternoon working from the April 29 TAO/TRITON report [Although the TAO/TRITON Graphic appears to update once a day, in reality it updates more frequently.], this is what I calculated.
Calculation of Nino 3.4 from TAO/TRITON Graphic
|Anomaly Segment||Estimated Anomaly|
|Last Week||This Week|
|A. 170W to 160W||-0.1||-0.1|
|B. 160W to 150W||-0.0||0.0|
|C. 150W to 140W||-0.3||-0.1|
|D. 140W to 130W||-0.5||-0.2|
|E. 130W to 120W||-0.3||-0.1|
Total divided by five i.e. the Daily Nino 3.4 Index
|(-1.2/5 = -0.2||(-0.1)/5 = -0.0|
My estimate of the daily Nino 3.4 SST anomaly tonight is 0.0 which is clearly an ENSO Neutral not a La Nina value. NOAA has reported the weekly Nino 3.4 to be warmer than last week at -0.0 which is clearly an ENSO Neutral value not a La Nina value and is the same value I have calculated. Nino 4 is reported to be warmer than last week at +0.4. Nino 3 is reported a bit warmer at -0.2. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported much warmer at -0.7. It was up there close to -3.0 at one time so this index has been declining as an anomaly (rising) quite a bit and also fluctuating quite a bit which is not surprising as it is the area most impacted by the Upwelling off the coast. So it is an indication of the interaction between surface water and rising cool water. Thus it is subject to larger changes. I am only showing the currently issued version of the NINO SST Index Table as the prior values are shown in the small graphics on the right with this graphic. The same data in graphic form but going back a couple of more years can be found here. The full table of values can be found here.
This graphic brings the Nino 3.4 up to date and is easy to read. It may be more reliable than the NOAA readings.
Here is another way of looking at the TAO/TRITON Graphic. It is a fast way to assess the strength of an ENSO Event and provides a way to track it.
The below table only looks at the Equator and shows the extent of anomalies along the Equator. The ONI Measurement Area is the 50 degrees of Longitude between 170W and 120W and extends 5 degrees of Latitude North and South of the Equator so the above table is just a guide and a way of tracking the changes. The top rows show El Nino anomalies. The two rows just below that break point contribute to ENSO Neutral.
Subareas of the Anomaly
|Westward Extension||Eastward Extension||Degrees of Coverage||Total by ENSO Phase|
Portion in Nino 3.4 Measurement Area
|These Rows below show the Extent of El Nino Impact on the Equator|
1C to 1.5C (strong)
|+0.5C to +1C (marginal)|
|These Rows Below Show the Extent of ENSO Neutral Impacts on the Equator|
|0.5C or cooler Anomaly (warmish neutral)|
|0C or cooler Anomaly (coolish neutral)|
|These Rows Below Show the Extent of La Nina Impacts on the Equator.|
|-0.5C or cooler Anomaly|
|-1.0C or cooler Anomaly|
|-1.5C or cooler Anomaly|
|-2.0C or cooler Anomaly|
|-2.5C or cooler Anomaly|
|This week 18 degrees of longitude along the Equator in the Nino 3.4 Measurement Area registers La Nina values. The other 32 degrees register Neutral. That is not the case for the full +5N and +5S width of the Nino 3.4 Measurement Area but in this analysis we are just looking at the Equator. Roughly speaking, the ratio of the Neutral Value to 50 tells us if we are close to being in Neutral. To some extent it is difficult to assess as the boundary of the cool water is the Equator so it is not clear how to count it.|
The next graphic overlaps with the subsequent topic but I will show it here.
The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2017. The anomaly had returned to zero then reversed for a month and then returned to zero and now has gone positive. In retrospect it was the Kelvin Wave (#1) Activity the Upwelling Phase and the MJO which caused the brief reversal of the warming trend.
A side by side comparison can be useful
|Comparison Week Probably Third Week of December 2017||Current Week|
Sea Surface Temperature and Anomalies
It is the ocean surface that interacts with the atmosphere and causes convection and also the warming and cooling of the atmosphere. So we are interested in the actual ocean surface temperatures and the departure from seasonal normal temperatures which is called “departures” or “anomalies”. Since warm water facilitates evaporation which results in cloud convection, the pattern of SST anomalies suggests how the weather pattern east of the anomalies will be different than normal.
A major advantage of the Hovmoeller method of displaying information is that it shows the history so I do not need to show a sequence of snapshots of the conditions at different points in time. This Hovmoeller provides a good way to visually see the evolution of this ENSO event. I have decided to use the prettied-up version that comes out on Mondays rather that the version that auto-updates daily because the SST Departures on the Equator do not change rapidly and the prettied-up version is so much easier to read. The bottom of the Hovmoeller shows the current readings. Remember the +5, -5 degree strip around the Equator that is being reported in this graphic. So it is the surface but not just the Equator.
This next graphic is more focused on the Equator and looks down to 300 meters rather than just being the surface.
We are back to a single Kelvin Wave phase in operation. The up-welling phase of Wave #1 reached South America and is no longer a factor re the Nino 3.4 Measurement Area but is a factor further east.. The down-welling phase of Wave #2 is at the 120W. The down-welling phase provided the warm water that ended 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. These currents are very complicated and made even more so by the uneven nature of the ocean floor. So the exact pattern of where this warm water will erupt is beyond my level of understanding. But it will erupt to the surface in multiple different places.
Now for a more detailed look. Below is the pair of graphics that I regularly provide. The date shown is the midpoint of a five-day period with that date as the center of the five-day period. The bottom graphic shows the absolute values, the upper graphic shows anomalies compared to what one might expect at this time of the year in the various areas both 130E to 90W Longitude and from the surface down to 450 meters. At different times I have discussed the difference between the actual values and the deviation of the actual values from what is defined as current climatology (which adjusts every ten years except along the Equator where it is adjusted every five years) and how both measures are useful for other purposes.
There is neutral water from the Dateline to beyond 100W but colder to the east. We now have warm water with a maximum anomaly of +4C developing west of the Dateline and crossing the Dateline at depth to 100W, the result of another Down-welling Kelvin Wave: Wave #2. La Nina is over but its demise is not yet acknowledged by NOAA.
We also see that the Warm Pool moving to the East does not appear to be sufficient to fully reverse the prior La Nina into a El Nino. Sometimes the human eye is better than a computer model with respect to pattern recognition.
|The 28C Isotherm is now east of the Dateline, the 27C Isotherm is at 150W, the 25C Isotherm is now at 100W and in many places at the surface further east. The 20C Isotherm still close to reaching the surface due to the cool water being pushed to the surface by Kelvin Wave #2.|
Tracking the change.
And now let us look at the atmosphere.
And Now the Air Pressure to Confirm that the Atmosphere is Reacting to the Sea Surface Temperature Pattern. The most Common way to do that is to use an Index called the SOI.
This index provides an easy way to assess the location of and the relative strength of the Convection (Low Pressure) and the Subsidence (High Pressure) near the Equator. Experience shows that the extent to which the Atmospheric Air Pressure at Tahiti exceeds the Atmospheric Pressure at Darwin Australia when normalized is substantially correlated with the Precipitation Pattern of the entire World. At this point there seems to be no need to show the daily preliminary values of the SOI but we can work with the 30 day and 90 day values.
Current SOI Readings
The 30 Day Average on April 30, 2018 was reported as + 4.02 which is an ENSO Neutral value. The 90 Day Average was reported at +1.83 which is also an ENSO Neutral value. Looking at both the 30 and 90 day averages is useful with the 90 day lagging the 30 day as one would expect. They are not in agreement at this point in time. The trend is down (i.e. less La Nina-ish). So Queensland in their forecast is basing it on a rising SOI and that forecast is shown elsewhere in this report. But the La Nina has ended. So their forecast is questionable at this point. But there are lags so it gets complicated. The Queensland forecast may update later tonight or tomorrow and I will update that map in this report when it it is available.
SOI = 10 X [ Pdiff – Pdiffav ]/ SD(Pdiff) where Pdiff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question. So really it is comparing the extent to which Tahiti is more cloudy than Darwin, Australia. During El Nino we expect Darwin Australia to have lower air pressure and more convection than Tahiti (Negative SOI especially lower than -7 correlates with El Nino Conditions). During La Nina we expect the Warm Pool to be further east resulting in Positive SOI values greater than +7).
To some extent it is the change in the SOI that is of most importance. The MJO or Madden Julian Oscillation is an important factor in regulating the SOI and Ocean Equatorial Kelvin Waves and other tropical weather characteristics. More information on the MJO can be found here. Here is another good resource.
Forecasting the Evolution of ENSO
|Here is the primary NOAA model for forecasting the ENSO Cycle.||The CDAS model is a legacy “frozen” NOAA system meaning the software is maintained but not updated. We find it convenient to obtain this graphic from Tropical Tidbits.com|
|This model is forecasting ENSO Neutral. Click here to see a month by month version of the same model but without some of the correction methodologies applied. It gives us a better picture of the further out months as we are looking at monthly estimates versus three-month averages.||Notice that since February, 2018 the Nino 3.4 Index has been rising. The CDAS data It is not in conflict with the primary NOAA model but shows daily values rather then smoothing them out like the CFSv2 Model does. The CDAS data has now risen to and even above -0.5C that had seemed to be a lid. That lid is being tested and most likely will be substantially reached soon. Will NOAA notice?|
The CFS.v2 is not the only forecast tool used by NOAA. The CPC/IRI Analysis which is produced out of The International Research Institute (IRI) for Climate and Society at Columbia University is also very important to NOAA.
Here is the most recent update.
IRI Technical ENSO Update
Published: April 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-April 2018, the NINO3.4 SST anomaly was at the level of warm-neutral to borderline La Niña. For March the SST anomaly was -0.73 C, indicating weak La Niña, and for January-March 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 -0.4, showing warm-neutral conditions. However, the pertinent atmospheric variables, including the lower level zonal wind anomalies, the Southern Oscillation Index and the anomalies of outgoing longwave radiation (convection), continue showing patterns suggestive of La Niña. On the other hand, subsurface temperature anomalies across the eastern equatorial Pacific have warmed to moderately above-average, suggesting that the dissipation of the La Niña is imminent, if not occurring right now. Given the current and recent SST anomalies, the subsurface profile and the conditions of most key atmospheric variables, it appears we are currently in transition from weak La Niña to neutral, ending the weak-to-moderate La Niña of 2017-18.
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 the March-May season. A La Niña Advisory was once again issued with that Discussion. The latest set of model ENSO predictions, from mid-April, now available in the IRI/CPC ENSO prediction plume, is discussed below. Those predictions also suggest that the SST is likely to return to neutral during within the March-May season.
As of mid-March, more than 90% of the dynamical or statistical models predict neutral conditions for the initial Apr-Jun 2018 season, with less than 10% showing a continuation of La Niña conditions. Over the course of the rest of 2018, probabilities for neutral remain greater than 50% through Sep-Nov, after which probabilities for El Niño rise to over 60% for Oct-Dec and over 70% for Nov-Jan and Dec-Feb 2018-19. 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 Jul-Sep 2018 season, among models that do use subsurface temperature information, 65% of models predicts neutral conditions and 35% predict El Niño conditions. For all models, predictions for La Niña probabilities are less than 10% for the Apr-Jun and May-Jul periods, and near zero during the second half of 2018.
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 approximately 10% for the full range of seasons, from Apr-Jun 2018 through to Dec-Feb 2018-19. Probabilities for neutral conditions begin at 90% for Apr-Jun, drop to about 60% for Jun-Aug and to less than 40% from Sep-Nov through the final season of Dec-Feb. Meanwhile the probabilities for El Niño, which begin at 0% for Apr-Jun, rise to about 30% for Jun-Aug, 40% for Jul-Sep, exceed 50% beginning with Sep-Nov and reach 60-65% for Nov-Jan and Dec-Feb 2018-19. 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 strong preference for ENSO-neutral from Apr-Jun to Jun-Aug 2018, approximately equal probabilities for neutral or El Niño conditions for Aug-Oct, followed by a period from Sep-Nov through Dec-Feb 2018-19 when El Niño conditions are between approximately 55% and 65% likely. Probabilities for La Niña are roughly 10% throughout the entire forecast period. 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.
And here is what is called the plume of a variety of forecast models.
Forecasts from Other Meteorological Agencies.
Here is the JAMSTEC Model Forecast
And the short discussion related to the April 1 ENSO forecast released recently
Apr. 24, 2018 Prediction from 1st Apr., 2018
The La Niña-like condition will disappear by late spring. Then the tropical Pacific will return to a normal state by fall and continue to be normal during the whole year.
Indian Ocean forecast:
Our ensemble average shows the evolution of a moderately positive Indian Ocean Dipole from late summer. 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.
On a seasonal scale, most part of the globe will experience a warmer-than-normal condition in summer, while some parts of northern Europe, some part of Russia, north of Mongolia, Pakistan and India will experience a cooler-than-normal condition. In fall, the cold anomaly spreads over whole Europe and central Russia. Most part of Canada will experience a relatively cold condition As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for India, southern West Africa, the Philippines, Indochina, and western U.S., while Indonesia, central China, North/South Korea, southern Europe, central Africa, and central U.S. will experience a drier-than-normal condition during boreal summer. In fall, we expect a drier-than-normal condition in Western Europe facing the Atlantic. Indonesia, Australia, New England in US will be drier than normal, as well. The drier condition in Indonesia and Australia may be due to the expected positive Indian Ocean Dipole.
Most part of Japan will experience warmer and relatively wetter-than-normal conditions in summer. Monthly prediction (not sown) suggests an active rainy season (Baiu) in June.
Here is the Nino 3.4 report from the Australian BOM (it updates every two weeks)
And the ENSO Outlook Discussion Issued on April 24, 2018
El Niño–Southern Oscillation expected to remain neutral through winter
In the tropical Pacific, the El Niño–Southern Oscillation (ENSO) remains neutral—neither El Niño nor La Niña. All climate models indicate the tropical Pacific Ocean will continue to warm slowly, but temperatures will remain close to average through the southern hemisphere winter.
Most atmospheric and oceanic indicators of ENSO are at neutral levels. Sea surface temperatures in the central Pacific are close to average for this time of year. Beneath the surface, the tropical Pacific Ocean is slightly warmer than average, but well within the neutral range. In the atmosphere, cloud patterns remain La Niña-like, but trade winds are close to average.
All international climate models surveyed by the Bureau suggest that sea surface temperatures in the tropical Pacific will continue to rise, but remain ENSO neutral for the remainder of the southern autumn and winter. By September, two of the eight models suggest ocean temperatures may approach El Niño thresholds.
Climate model outlooks for ENSO and the IOD have lower accuracy during autumn than at other times of the year. Hence current model outlooks for these climate drivers should be viewed with some caution.
Indian Ocean IOD (It updates every two weeks)
Indian Ocean Dipole Outlook Discussion Issued April 24, 2018
The Indian Ocean Dipole (IOD) is currently neutral. The weekly index value to 22 April was −0.03 °C.
Three of the six international climate models surveyed by the Bureau anticipate that the IOD will become negative IOD during the southern hemisphere winter. A negative IOD during winter tends to enhance rainfall across southern Australia.
It should be noted that outlook skill is lower at this time of year.
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 La Nina Conditions along the Equator have come to an end. The actual impacts on Worldwide weather lag the change in conditions along the Equator so we may have impacts from this transitioning La Nina for a short period of time but these impacts seem to be tailing off quite dramatically.
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
Nothing to Report
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.
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.
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|
|Eastern Pacific Easterlies|
|Western Pacific Westerlies|
|MJO Active Phase|
|MJO Inactive Phase|
History of ENSO Events as measured by the ONI
The new SON reading of -0.8 is the fifth La Nina Reading. Not all Meteorological Agencies Worldwide will necessarily accept this La Nina to be legitimately declared but most will. The full history of the ONI readings can be found here. The MEI index readings can be found here.
Four Quadrant Jet Streak Model Read more here This is very useful for guessing at weather as a trough passes through. It would apply to the states that are at the apex of the trough.
If the centripetal accelerations owing to flow curvature are small, then we can use the “straight” jet streak model. The schematic figure directly below shows a straight jet streak at the base of a trough in the height field. The core of maximum winds defining the jet streak is divided into four quadrants composed of the upstream (entrance) and downstream (exit) regions and the left and right quadrants, which are defined facing downwind.
Isotachs are shaded in blue for a westerly jet streak (single large arrow). Thick red lines denote geopotential height contours. Thick black vectors represent cross-stream (transverse) ageostrophic winds with magnitudes given by arrow length. Vertical cross sections transverse to the flow in the entrance and exit regions of the jet (J) are shown in the bottom panels along A-A’ and B-B’, respectively. Convergence and divergence at the jet level are denoted by “CON” and “DIV”. “COLD” and “WARM” refer to the air masses defined by the green isentropes.
[Editor’s Note: There are many undefined words in the above so here are some brief definitions. Isotachs are lines of equal wind speed. Convergence is when there is an inflow of air which tends to force the air higher with cooling and cloud formation. Divergence is when there is an outflow of air which tends to result in air sinking which causes drying and warming, Confluence is when two streams of air come together. Diffluence is when part of a stream of air splits off.]
Here is a time sequence animation. You may have to click on them to get the animation going.
When we discuss the jet stream and for other reasons, we often discuss different layers of the atmosphere. These are expressed in terms of the atmospheric pressure above that layer. It is kind of counter-intuitive to me. The below table may help the reader translate air pressure to the usual altitude and temperature one might expect at that level of air pressure. It is just an approximation but useful.
Re the above, H8 is a frequently used abbreviation for the height of the 850 millibar level (which is intended to represent the atmosphere above the Boundary Layer most impacted by surface conditions), H7 is the 700 mb level, H5 is the 500 mb level, H3 is the 300 mb level. So if you see those abbreviations in a weather forecast you will know what they are talking about.
Tropical Activity Possibly Impacting CONUS.
When there is activity and I have not provided the specific links to the storm of “immediate” interest, one can obtain that information at this link. At this point in time, no (new) tropical events are expected to appear in this graphic during the next 48 hours. If that changes, we will provide an update.
Now let us look at the Western Pacific in Motion.
The above graphic which I believe covers the area from the Dateline west to 100E and from the Equator north to 45N normally shows the movement of tropical storms towards Asia in the lower latitudes (Trade Winds) and the return of storms towards CONUS in the mid-latitudes (Prevailing Westerlies). This is recent data not a forecast. But, it ties in with the Week 1 forecast in the graphic just above this graphic. Information on Western Pacific storms can be found by clicking here. This (click here to read) is an unofficial private source but one that is easy to read.
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