Written by Sig Silber
Both the NOAA and JAMSTEC forecasts are signaling ENSO Neutral this winter but JAMSTEC shows near-El Nino conditions for January 2018 while NOAA shows near-La Nina Conditions for the same month. The sum of the difference is 1C in the ENSO Index for January 2018 which is a significant difference. Thus the North American forecasts for the Second Period namely DJF i.e. the winter of 2017/2018 are very different in the two forecasts. And the forecasts for the third period, Spring, are also very different. JAMSTEC projects a very cold winter for Europe.
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In this Update, we compare the JAMSTEC temperature and precipitation forecast maps, which are for the World, with the NOAA temperature and precipitation forecast maps that cover only CONUS and Alaska. We do this primarily for educational purposes. Remember: these are forecasts not guarantees. But the differences between the NOAA and JAMSTEC forecasts are dramatically different this time.
Some Housekeeping Issues.
The next Regular Weekly Weather and Climate Report will be published on July 24. If you are reading this Update Report and wish to transfer to the Current Weather and Climate Report, Click Here for the list of Weather Posts. That link takes you to the archive of all weather articles written by Sig Silber so you can if the new Weekly Weather Report has been published go there or back to an earlier report but please keep in mind that the graphics in earlier reports in some cases auto-update and the text may no longer apply to the graphics shown. 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.
Now we Begin Our Report
Below is a quick summary of the temperature and precipitation forecasts for three time periods and from left to right the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S), then JAMSTEC for North America (which includes Canada and Northern Mexico), and then JAMSTEC for Europe and surrounding areas. Larger graphics are provided later in the report. It is kind of a tease to keep you reading but you can see the evolution of the weather pattern through Fall, Winter and into Spring. For some readers, these two sets of summary graphics may be all the information they wish to look at and that is fine.
Temperature
| NOAA Alaska Plus CONUS | JAMSTEC North America | JAMSTEC Europe | |
SON 2017 Temp |  |  |  |
DJF 2017/2018 Temp |  |  |  |
MAM 2018 Temp |  |  |  |
Precipitation
| NOAA Alaska Plus CONUS | JAMSTEC North America | JAMSTEC Europe | |
SON 2017 Precip |  |  |  |
DJF 2017/2018 Precip |  |  |  |
MAM 2018 Precip |  |  |  |
NOAA Updated Seasonal Outlook
NOAA issued their updated Seasonal Outlook on the third Thursday of the month i.e. July 20, 2017 as is their normal schedule. JAMSTEC was a week earlier than NOAA this month. Let’s first take a look at the NOAA maps. Then we will compare the NOAA Maps to those issued by JAMSTEC. A note about terminology; the deviations from climatology/normal are color coded but also labeled “A” for more than normal and “B” for less than normal. The area designated EC means Equal Chances of being more or less than normal. JAMSTEC relies on their color coding. In my comments I have used EC to cover all the situations where a clear anomaly is not shown.
First we will take a look at the Early Outlook for August 2017. It is called the Early Outlook because it will be updated at the end of July. Only the August Outlook will be updated at that time.
Temperature
Precipitation
We have nothing to compare these maps with as NOAA does not in their Update provide a forecast for two months out separate from their three-month forecast. Thus I do not have August maps from the June 15, NOAA Report to compare against. And July is not over so we can not really compare the August forecast against July actual. It is probably best to just try to understand what NOAA is trying to convey about August which can be summarized as for temperature warm almost everywhere and for precipitation EC almost everywhere except wet in an area associated with the Southwest Monsoon which also will receive relief from the heat and be EC.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. August/September/October is shown as ASO. You will see such abbreviations often in this report.
Prior Temperature Outlook for ASO 2017
New Temperature Outlook for ASO 2017
Prior Precipitation Outlook for ASO 2017
New Precipitation Outlook for ASO 2017
Now let us focus on the long-term situation and compare the new set of maps with the maps issued on June 15, 2017.
Prior 14 Month Temperature Outlook: ASO 2017 – JAS 2018
New 14 Month Temperature Outlook: SON 2017 – ASO 2018
To compare maps from one release to another, one needs to remember that the new release drops one three-month period and adds a later one. So to make the comparisons one has to shift the new maps to the right one position and that makes the map on the right drop down to become the left-most map in the next level. I do not have a computer software tool for doing that for you so you have to do it mentally. When I do the comparison, I print the two sets of maps and put them side by side and number the same three-month maps 1, 2, 3,…..,11 in both sets of maps to make it easier for me to easily compare the same three-month period in the new with the previous forecast. One uses the same procedure to compare the precipitation maps. Based on this procedure, I conclude that:
Prior 14 Month Precipitation Outlook: ASO 2017 – JAS 2018
New 14 Month Precipitation Outlook: SON 2017 – ASO 2018
If you want larger versions of each map (temperature and precipitation) you can find them here. And then each of those maps can be clicked on to further enlarge them.
Sometimes it is useful to compare the present month outlook to the three-month outlook
One can mentally subtract the August Outlook from the three-month Outlook and create the Outlook for the last two months in the three-month period namely September and October 2017. To do that you need to take into account that:
* 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.
Discussion
Below are excerpts (significantly reorganized and with some of the redundancy removed) from the Discussion released by NOAA on July 20, 2017.
Headings that are “Initial Cap” only rather than all caps were added by the Author of this Update Report for clarity. Also we have organized the sequence of the sections of NOAA Discussion to first present the Atmospheric and Oceanic Conditions and then the Current Month, the Three or Four-month period, and finally the remainder of the 15 Month Forecast. We think that sequence with the three- to four-month period broken out separately, makes the discussion more useful for more readers.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
OCEANIC AND ATMOSPHERIC OBSERVATIONS ACROSS THE EQUATORIAL PACIFIC INDICATE ENSO-NEUTRAL CONDITIONS. WHILE SEA SURFACE TEMPERATURES (SSTS) ARE SLIGHTLY ABOVE AVERAGE IN THE EAST-CENTRAL PACIFIC OCEAN, ATMOSPHERIC CONDITIONS ARE REPRESENTATIVE OF ENSO-NEUTRAL CONDITIONS. THE OBSERVED WEEKLY SSTS CENTERED ON JULY 12 INDICATE POSITIVE SST ANOMALIES OF 0.5 TO 1 DEGREE C JUST TO THE WEST OF THE DATE LINE AND FROM ABOUT 170W TO 120W LONGITUDE ALONG THE EQUATOR. THE UPPER-OCEAN TEMPERATURE ANOMALY IS ABOVE AVERAGE ACROSS MUCH OF THE EQUATORIAL PACIFIC OCEAN TO A DEPTH OF 100 TO 150 METERS, THOUGH WITH WEAK ANOMALIES OF LESS THAN 2 DEGREES C.
DESPITE WARMER-THAN-AVERAGE OCEAN TEMPERATURES ACROSS THE CENTRAL AND EASTERN PACIFIC SINCE MARCH, ATMOSPHERIC CONVECTIVE ANOMALIES FROM JUNE 17 TO JULY 12 CONTINUE TO REMAIN NEAR AVERAGE FROM NEAR THE DATE LINE TO THE EASTERN TROPICAL PACIFIC. ENHANCED CONVECTION WAS OBSERVED ACROSS PARTS OF INDONESIA DURING THIS TIME PERIOD. WESTERLY ANOMALIES IN LOWER LEVEL WINDS AT 850-HPA WERE OBSERVED OVER THE EAST-CENTRAL TROPICAL PACIFIC, WHILE EASTERLY ANOMALIES WERE OBSERVED IN UPPER LEVEL 200-HPA WINDS OVER THE EASTERN PACIFIC. THESE ATMOSPHERIC INDICATORS ARE CONSISTENT WITH ENSO-NEUTRAL CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
MOST MODELS OF THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) INDICATE A CONTINUATION OF ENSO-NEUTRAL CONDITIONS THROUGH THE AUTUMN, WITH SOME MODELS INDICATING WEAK TO MODERATE EL NINO CONDITIONS. THE NCEP CFSV2 PREDICTS NEAR-ZERO TEMPERATURE ANOMALIES IN THE EAST-CENTRAL TROPICAL PACIFIC OCEAN BY THE BEGINNING OF AUTUMN. THE CPC NINO 3.4 SST CONSOLIDATION OF THE CFS AND STATISTICAL FORECASTS INDICATES ELEVATED PROBABILITIES OF POSITIVE TEMPERATURE ANOMALIES THROUGH SON, AND A TEMPERATURE ANOMALY CLOSE TO ZERO DEGREES IS MOST LIKELY BY OND. THE CPC/IRI CONSENSUS FORECAST INDICATES PERSISTENCE OF ENSO-NEUTRAL CONDITIONS IS MOST LIKELY THROUGH FMA 2018 WITH A PROBABILITY GREATER THAN 50%, WHILE THE PROBABILITY OF DEVELOPMENT OF EL NINO CONDITIONS REMAINS ELEVATED FROM CLIMATOLOGICAL PROBABILITIES AND IS AT OR ABOVE 35% THROUGH OND.
30-DAY OUTLOOK DISCUSSION FOR AUGUST 2017
THE AUGUST 2017 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL MODEL GUIDANCE, STATISTICAL TOOLS, CURRENT SOIL MOISTURE CONDITIONS, AND POTENTIAL INFLUENCES FROM MODES OF TROPICAL VARIABILITY. ENSO IS NOT A FACTOR IN THESE OUTLOOKS SINCE IT IS IN A NEUTRAL STATE AND IS PREDICTED TO REMAIN NEUTRAL.
THE MADDEN-JULIAN OSCILLATION (MJO) BECAME MORE COHERENT DURING MID-JULY WITH ITS ENHANCED PHASE OVER THE WESTERN MARITIME CONTINENT. A COHERENT MJO SIGNAL IS FAVORED TO PROPAGATE EASTWARD DURING THE NEXT TWO WEEKS, BUT ITS EFFECTS ON THE EXTRATROPICS ARE EXPECTED TO BE MINIMAL GIVEN THE TIME OF YEAR. THE CFS MODEL INDICATES AN ATMOSPHERIC KELVIN WAVE (KW) CROSSING THE WESTERN HEMISPHERE DURING LATE JULY INTO THE BEGINNING OF AUGUST. THIS KW COULD PROVIDE A FAVORABLE ENVIRONMENT FOR TROPICAL CYCLONE DEVELOPMENT OVER THE EAST PACIFIC AND CONTRIBUTE TO A CONTINUATION OF ENHANCED MOISTURE ACROSS THE SOUTHWESTERN U.S.
Temperature
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) DEPICTS INCREASED PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ACROSS NEARLY ALL OF THE CONTINENTAL U.S. THE LARGEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES IN THE OFFICIAL OUTLOOK ARE FORECAST ACROSS THE NORTHERN GREAT PLAINS WHERE CURRENT SOIL MOISTURE VALUES RANK BELOW THE 10TH PERCENTILE. ALSO, THE GFS, ECMWF, AND CANADIAN ENSEMBLE MEANS INDICATE THAT THE ANOMALOUS 500-HPA RIDGE IS LIKELY TO PERSIST AT LEAST THROUGH THE BEGINNING OF AUGUST. ALTHOUGH MANY OF THE DYNAMICAL MODELS FAVOR ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHWESTERN U.S., EQUAL CHANCES FOR BELOW-, NEAR-, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR THIS REGION BASED ON A CONSISTENT SIGNAL AMONG DAILY RUNS OF THE NCEP CLIMATE FORECAST SYSTEM (CFS) MODEL, DEPICTING NEAR TO BELOW-NORMAL TEMPERATURES, AND THE ENHANCED ODDS FOR ABOVE-MEDIAN PRECIPITATION FORECAST IN THE PRECIPITATION OUTLOOK.
Precipitation
THE PROBABILITY ANOMALY CORRELATION (PAC) CALIBRATED PROBABILITY FORECAST FROM THE NMME FEATURES LITTLE IF ANY SIGNAL THROUGHOUT MOST OF THE FORECAST DOMAIN WITH ONLY A SLIGHT TILT IN THE ODDS (36 TO 40 PERCENT) FOR THE ABOVE NORMAL TERCILE FROM THE RIO GRANDE VALLEY NORTH TO THE CENTRAL ROCKIES. THE MOST CONSISTENT SIGNAL AMONG DAILY CFS MODEL RUNS IS A FAVORED AREA OF ABOVE-MEDIAN PRECIPITATION OVER THE RIO GRANDE VALLEY AND PARTS OF THE WESTERN U.S. BASED ON THESE TWO PRECIPITATION TOOLS ALONG WITH POTENTIAL INFLUENCES FROM AN EXPECTED ACTIVE PERIOD OF EAST PACIFIC TROPICAL CYCLONE ACTIVITY, ABOVE-MEDIAN PRECIPITATION IS FAVORED FOR THE RIO GRANDE VALLEY, MOST OF THE MONSOON REGION OF THE SOUTHWESTERN U.S., AND THE CENTRAL ROCKIES. FORECAST CONFIDENCE IN THE PRECIPITATION OUTLOOK IS LIMITED DUE TO THE LACK OF PREDICTABILITY OF CONVECTIVE RAINFALL ON A MONTHLY TIME SCALE.
Alaska
THE DYNAMICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH INCREASED CHANCES OF ABOVE-NORMAL TEMPERATURES ACROSS ALASKA. THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE FORECAST ACROSS THE ALASKA PENINSULA ALONG WITH PARTS OF WESTERN AND SOUTHERN ALASKA, BASED IN PART ON SEA SURFACE TEMPERATURES AVERAGING 1 TO 3 DEGREES C ABOVE NORMAL. THE DYNAMICAL MODEL CONSENSUS FAVORS A RELATIVELY WET AUGUST ACROSS WESTERN ALASKA.
Three-Month Outlook ASO 2017
Temperature
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS ALL OF THE FORECAST DOMAIN FOR THE ASO OUTLOOK, AS WELL AS OUTLOOKS FOR SON 2017 THROUGH NDJ 2017-2018, AS INDICATED BY A CONSENSUS OF MODELS FROM THE NMME, DRIVEN SOMEWHAT BY DECADAL TEMPERATURE TRENDS. LOWER PROBABILITIES FOR ABOVE NORMAL TEMPERATURES ARE INDICATED FOR ASO AND SON FROM PARTS OF TEXAS AND THE SOUTHERN PLAINS TO THE CENTRAL MISSISSIPPI VALLEY, DUE TO POTENTIAL MODERATION OF TEMPERATURES BY INCREASED SOIL MOISTURE IN RESPONSE TO PREDICTED PRECIPITATION IN THIS REGION. THE HIGHEST PROBABILITIES OF ABOVE NORMAL TEMPERATURES IN ASO ARE INDICATED FOR PARTS OF THE NORTHERN ROCKIES AND INTERMOUNTAIN WEST, AS WELL AS ALONG THE GULF AND ATLANTIC COASTS, AND THE NORTHEAST, WHERE DECADAL TRENDS ARE GREATER IN COMPARISON TO SEASONAL VARIABILITY. PROBABILITIES IN THE SOUTHWEST, WHERE DECADAL TRENDS ARE ALSO LARGE, ARE MODERATED BY A FORECAST FOR ABOVE MEDIAN PRECIPITATION AND RESULTING SURFACE-ATMOSPHERIC FEEDBACKS. PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE ALSO HIGHEST FOR PARTS OF SOUTHWESTERN, WESTERN AND NORTHWESTERN ALASKA, AS INDICATED BY THE PROBABILITY FORECASTS OF THE NMME, LARGELY RESULTING FROM DECADAL TRENDS.
Precipitation
THE ASO 2017 PRECIPITATION OUTLOOK INDICATES AN INCREASED CHANCE FOR ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE SOUTHERN PLAINS, THE SOUTHWEST, SOUTHWESTERN ALASKA, AND THE ALEUTIAN ISLANDS. [Editor’s Note: The discussion later under ASO 2017 TO ASO 2018 provides more information on ASO 2017 precipitation but I could not figure out a good way to subdivide the NOAA discussion into SON and later months.]
PROGNOSTIC DISCUSSION OF OUTLOOKS – ASO 2017 TO ASO 2018 (with focus on the months beyond ASO.
DYNAMICAL MODELS PROVIDE THE PRIMARY GUIDANCE FOR THE SEASONAL OUTLOOKS THROUGH DJF 2017-2018, WITH DECADAL TEMPERATURE AND PRECIPITATION TRENDS PROVIDING THE PRIMARY GUIDANCE FOR LONGER LEADS. THE CALIBRATED PROBABILITY FORECASTS FROM THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND ANOMALY FORECASTS FROM ITS INDIVIDUAL MODELS, INCLUDING THE NCEP CFS, WERE USED THROUGH DJF 2017/2018. THE DECREASING LIKELIHOOD OF EL NINO DEVELOPMENT, COMPARED TO PREVIOUS OUTLOOKS LED TO ADJUSTMENTS IN THE OUTLOOKS, ESPECIALLY FOR THE WINTER SEASONS.
TEMPERATURE
WITH ENSO-NEUTRAL CONDITIONS MOST LIKELY THROUGH WINTER, THE TEMPERATURE OUTLOOKS FROM ASO 2017 TO DJF 2017-18 ARE BASED PRIMARILY ON THE NMME CALIBRATED PROBABILITY FORECASTS. AN EXPECTED LACK OF SEA ICE ELEVATES CHANCES FOR ABOVE-NORMAL TEMPERATURES ACROSS NORTHERN ALASKA DURING THE AUTUMN. DECADAL TRENDS ARE USED AS GUIDANCE FOR THE TEMPERATURE OUTLOOKS AT LONGER LEADS FROM MAM TO ASO 2018 AND INDICATE INCREASED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES WHERE TRENDS ARE THE LARGEST RELATIVE TO SEASONAL TEMPERATURE VARIABILITY.
PRECIPITATION
ENHANCED PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION FOR THE NORTHERN PLAINS DURING THE FIRST SEVERAL LEADS IN LAST MONTHS OUTLOOKS HAVE BEEN REMOVED FROM THE CURRENT OUTLOOKS, WHERE EQUAL CHANCES IS NOW INDICATED. THIS CHANGE IS BASED ON THE MOST RECENT DYNAMICAL MODEL GUIDANCE FROM THE NMME AND CFS. CALIBRATED PRECIPITATION PROBABILITY FORECASTS FROM THE NMME INDICATE ABOVE MEDIAN PRECIPITATION IS MOST LIKELY FOR PARTS OF TEXAS AND THE SOUTHERN PLAINS EXTENDING EASTWARD TO THE MISSISSIPPI RIVER. THIS SIGNAL CONTINUES IN THE OUTLOOKS FOR SON 2017 THROUGH DJF 2017-2018. A CONSENSUS OF THE DYNAMICAL MODELS INDICATE AN INCREASED CHANCE OF BELOW MEDIAN PRECIPITATION FOR PARTS OF PACIFIC NORTHWEST FOR ASO. THE AUGUST PRECIPITATION FORECASTS FROM THE MOST RECENT RUNS OF THE CFS AND ADDITIONAL DYNAMICAL MODEL FORECASTS FOR THE BEGINNING OF AUGUST CONSISTENTLY INDICATE ABOVE MEDIAN PRECIPITATION FOR AUGUST IN THE SOUTHWEST MONSOON REGION. AS THE MONTH OF AUGUST HAS GREATER PRECIPITATION IN THIS REGION THAN THE FOLLOWING MONTHS, ENHANCED PRECIPITATION IN AUGUST HAS AN INCREASED IMPACT ON THE TOTAL SEASONAL PRECIPITATION. ABOVE MEDIAN PRECIPITATION IS THEREFORE INDICATED FOR THE SOUTHWEST FOR ASO. ABOVE MEDIAN PRECIPITATION IS INDICATED FOR PARTS OF SOUTHERN ALASKA IN ASO 2017 THROUGH DJF 2017-2018, AS INDICATED BY CALIBRATED PRECIPITATION PROBABILITY FORECASTS FROM THE NMME. DUE TO DECADAL TRENDS, ABOVE MEDIAN PRECIPITATION IS MOST LIKELY FOR PARTS OF THE NORTHERN PLAINS AND GREAT LAKES REGION FROM MAM TO MJJ 2018, AND FOR PARTS OF THE NORTHEAST FROM MJJ THROUGH ASO 2018.
SINCE THE PREVIOUS OUTLOOK, THE CHANCES FOR EL NINO DEVELOPMENT DURING THE AUTUMN AND WINTER HAVE DECREASED. GIVEN THE LATEST ENSO FORECAST INDICATING A GREATER CHANCE OF ENSO-NEUTRAL CONDITIONS THROUGH THE WINTER, THE INCREASED CHANCES FOR BELOW MEDIAN PRECIPITATION FOR PARTS OF THE NORTHERN ROCKIES [Editor’s Note: Probably better described as the Northwest] IN NDJ AND DJF 2017-2018 HAVE BEEN REMOVED. PRECIPITATION OUTLOOKS FROM JFM THROUGH FMA 2018 ARE BASED ON THE SEASONAL PRECIPITATION CONSOLIDATION FORECAST AND DECADAL TRENDS.
Forecasting the Evolution of ENSO
Here is the JAMSTEC July 1 forecast of the Nino 3.4 values which are the most looked at index used to forecast El Nino.
Here is the discussion that corresponds to the JAMSTEC July 1 Nino 3.4 Forecast.
Jul. 13, 2017
Prediction from 1st Jul., 2017
ENSO forecast:
A slightly warmer-than-normal sea surface temperature is predicted for the whole tropical Pacific. This condition will persist until boreal winter. Then, it will return into a neutral state by next spring.
Indian Ocean forecast:
All ensemble members of SINTEX-F continue to predict a positive Indian Ocean Dipole [Editor’s Note: The Australian BOM disagrees see BOM graphic and discussion below] ; the ensemble mean prediction suggests that it peaks in boreal fall. In accord to the positive IOD evolution, sea level anomalies are expected to be negative (positive) in the eastern (western) tropical Indian Ocean.
Regional forecast:
On a seasonal scale, most part of the globe will experience a warmer-than-normal condition, while some parts of central Russia and central U. S. will experience a colder-than-normal condition in the boreal fall.
As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for some parts of East Africa and West Africa during the boreal fall, whereas most parts of Indonesia, Australia, eastern China, and Brazil will experience a drier condition during the boreal fall. Those are partly due to the positive Indian Ocean Dipole.
Most parts of Japan will experience moderately warmer-than-normal and drier-than-normal conditions in the boreal fall. The wind and pressure anomalies averaged in September-November suggest that Japan might be covered by an equivalent barotropic high. Those may be due to the combined effect of “the monsoon-desert mechanism” of the positive Indian Ocean Dipole and “the Silk Road pattern” along the Asian jet.
Here is the latest NOAA forecast of Nino 3.4 temperature anomalies. You can see the “blue” newer model runs and the “red” older model runs. The Oceanic Niño Index (ONI) which is the three-month rolling average of the Nino 3.4 values is NOAA’s primary indicator for monitoring El Niño and La Niña. The secondary indicator is the Southern Oscillation Index (SOI) which is based on the extent that the air pressure anomaly in Tahiti exceeds the air pressure anomaly in Darwin Australia. It is a complicated formula and is intended to assess the response of the atmosphere to the changes in the pattern of warm and cool sea surface temperatures.
El Nino Probabilities used by NOAA in Their Forecast (The forecast for the value of the Nino 3.4 Index receives the most attention).
And now we have the IRI/CPC July 19, 2017 fully model-based report on the right and the earlier July 13 less formal mostly based on a Meteorologist survey on the left.
Here is the discussion that accompanied the new release from CPC/IRI. Sometimes this discussion has a lot of value as the NOAA Outlook probably does not consider the most recent release from IRI due to timing overlap but the outlook has not changed during the past week. So this discussion and the discussion released by NOAA are probably very similar. I thought about not including this discussion but decided that some might find the added detail informative.
IRI ENSO Forecast IRI Technical ENSO Update Published: July 19, 2017
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-July 2017, the NINO3.4 SST anomaly was at the borderline of a weak El Niño level. For June the SST anomaly was 0.55 C, just inside the category of weak El Niño, and for Mar-May it was 0.44 C, in the upper part of the ENSO-neutral 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 0.5, at the threshold of minimal El Niño. The pertinent atmospheric variables, including the upper and lower level zonal wind anomalies, have been showing neutral patterns. The Southern Oscillation Index (SOI) and the equatorial SOI have been near average to somewhat below average, weakly indicating an El Niño tendency. Subsurface temperature anomalies across the eastern equatorial Pacific have been somewhat above average. However, given the combination of the SST and the atmospheric conditions, an ENSO-neutral diagnosis still remains appropriate.
Expected Conditions
What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it stated that ENSO-neutral has an approximately 50 to 55% chance of persisting from northern summer through fall and into winter, with somewhat lower chances for El Niño development. The latest set of model ENSO predictions, from mid-July, now available in the IRI/CPC ENSO prediction plume, is discussed below. Those predictions suggest that the SST has the greatest chance for being in the ENSO-neutral range for July-September and show a likelihood of just 35-40% for El Niño development in fall and early winter.
As of mid-July, 79% of the dynamical or statistical models predicts neutral ENSO conditions for the initial Jul-Sep 2017 season, while 21% predicts El Niño conditions and 0% predicts La Niña conditions. 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 Oct-Dec 2017 season, among models that do use subsurface temperature information, no model predicts La Niña conditions, 25% predicts El Niño conditions, while 75% predicts neutral ENSO. For all model types, the probabilities for La Niña are 5% or less for for all predicted seasons from Jul-Sep 2017 through Mar-May 2018. The probability for El Niño conditions is between 20 and 29% through Oct-Dec, rises to 30% or more for Nov-Jan through Jan-Mar 2018, and then decreases again through Mar-May 2018. Chances for neutral ENSO conditions are mainly between 70 and 80% through Nov-Jan 2017-18, decreasing to 65-70% for Dec-Feb and Jan-Mar 2018, and then rising to 75% or greater through Mar-May 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 about 15% or less from Jul-Sep 2017 through the final season of Mar-May 2018, with highest probabilities at 16% during Nov-Jan. Probabilities for ENSO-neutral are more than 65% for Jul-Sep, dropping to slightly below 50% from Oct-Dec to Dec-Feb, and rising to about 60% for the final seasons of Feb-Apr and Mar-May 2018. Probabilities for El Niño are about 30 to 40% from Jul-Sep to Mar-May 2018, peaking at 38-39% from Oct-Dec to Jan-Mar. 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 preference for ENSO-neutral throughout the forecast period, with chances for El Niño peaking at just below 40% during fall and winter. Chances for La Niña are relatively low throughout the 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 in early June by CPC and IRI, which will include some human judgment in combination with the model guidance.
A look at the subsurface along the Equator is very useful.
It could well be that the every ten year adjustment adjustment mechanism NOAA uses for the base climatology of the Tropical Pacific for real time analysis (OISSTv2 data set) is not able to keep up with Ocean Warming which may slightly overstate warm anomalies. Even the five year adjustment they use to review the data for historical analysis (ERSSTv4) really does not help very much when there is a trend that is either a secular trend due to Global Warming or part of a sixty-year low-frequency cycle such as the PDO. Current values tend to be higher than the average.
Normally La Nina Conditions are confirmed by SOI 30 day values that are greater than or equal to +7.0. El Nino Conditions are confirmed by SOI 30 day values that are less than or equal to -7.0. So right now both the Nino 3.4 Index and the SOI remain in the ENSO Neutral phase of ENSO but June recorded as an El Nino value. You can also see that month to month there has been a lot of fluctuation and that is thought to also impact weather perhaps as much as the absolute value of SOI.
Here is the Nino 3.4 report from the Australian BOM (it updates every two weeks)
Discussion Issued July 16, 2017
Tropical Pacific Ocean warmer than average, but ENSO neutral to stay for 2017
he El Niño-Southern Oscillation (ENSO) remains neutral. All climate models surveyed by the Bureau indicate the tropical Pacific Ocean is likely to stay ENSO neutral for the rest of 2017.
Sea surface temperatures (SSTs) in the central tropical Pacific (the NINO3.4 region) have been warmer than average, though still in the neutral range, since mid-April. The current NINO3.4 value of +0.5 °C is the result of a localised warm anomaly. The overall sea surface temperature pattern is inconsistent with a developing El Niño, meaning further ocean warming and El Niño development remains unlikely. This is reflected in neutral ENSO outlooks from all international climate models surveyed. Other indicators of ENSO, such as the Southern Oscillation Index, cloudiness near the Date Line, and trade winds also remain at neutral levels.
The Australian BOM employs a different threshold for considering a SSTA to be either La Nina or El Nino. Note their forecast is showing ENSO Neutral through their forecast period. This report will be updated in a few days but we can only work from what has been published and is available.
The ENSO forecasts are not the only factor that is considered when making these fairly long-term forecasts but it is a very major factor so that ENSO forecast strongly influences the Temperature and Precipitation forecasts. I have not presented the Australian BOM forecast for the Indian Ocean Dipole (IOD) but it differs dramatically from the JAMSTEC forecast which is covered in the JAMSTEC discussion of their Nino 3.4 forecast. This difference impacts mostly the forecasts for nations bordering the Indian Ocean.
Now the Comparison of the NOAA and JAMSTEC Forecasts. I am only discussing the differences for CONUS since NOAA does not cover the World in this set of forecasts. But the JAMSTEC World forecast is here for you to see and I comment on the highlights of that forecast also.
JAMSTEC works in three-month intervals and does not change the selection of months each time they update. So we have SON 2017, DJF 2017-2018, and MAM 2018 to work with from JAMSTEC and and we will use the same three-month periods from NOAA for comparison purposes. In two updates out of three they do not line up perfectly in the first three-month period and this is one of the two times where it is not perfect which we correct for this month by starting our comparison with SON so that we are working with exactly the same three months. In a way it is a shame that we can not compare the NOAA ASO to the JAMSTEC ASO but when you are comparing three-month periods exactly when you start is not that significant since the major interest is about the future not the near term. The NOAA analysis presented earlier in this report is very complete re ASO.
I show the NOAA Maps first followed by the JAMSTEC maps. I extract North America from the Worldwide JAMSTEC map and use that to compare with the NOAA Maps. I also extract and enlarge the Europe Section of the Worldwide JAMSTEC maps.
SON 2017
Temperature
NOAA SON 2017
And here is the SON temperature forecast for North America that I extracted from the JAMSTEC World Forecast
And now the JAMSTEC WORLD FORECAST
Precipitation
NOAA SON 2017
And here is the SON 2017 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast.
JAMSTEC WORLD FORECAST
DJF 2017/2018
Temperature
NOAA DJF 2017 – 2018
And here is the DJF 2017 – 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Precipitation
NOAA DJF 2017 – 2018
And here is the DJF 2017 – 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
MAM 2018
Temperature
NOAA MAM 2018
And here is the MAM 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Precipitation
NOAA MAM 2018
And here is the MAM 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Conclusion
Both forecasts are based on no El Nino. But the winter bias of JAMSTEC is a near El Nino and the winter bias of NOAA is a near La Nina. That adds up re the Nino 3.4 Index to a difference of 1C which if it was starting from pure Neutral would be either an El Nino or La Nina. As it is the two deviations from Nino 3.4 = 0 are of opposite signs so both forecasts are for ENSO Neutral Conditions for January 2018 but they are biased in different directions so this produces different forecasts.
End Note
A final comment about temperature. One normally sees more temperature anomalies in these maps than precipitation anomalies. The adjustment mechanism for trends in most cases involves adjusting the norm or “climatology” every decade to calculate a three-decade average and in the special case of the Equatorial Pacific for purposes of assessing in retrospect the ENSO anomalies, the adjustment is made very five years. When there is a rising temperature trend, the average tends to be lower than the current values so one tends to see more warm anomalies than cool anomalies. That same problem does not exist with precipitation or if it does, it may exist in the opposite direction but at a much lower magnitude as the Planet may be getting wetter as it gets warmer. So far no one has come up with a good solution for dealing with trends some of which may be long cycles and some may be secular trends. It is worth being aware of especially when we have fixed criteria for how to interpret anomalies.
