Written by Sig Silber
Yesterday we published a partial analysis of seasonal outlooks – namely the Update issued by NOAA on August 17, 2017. We could not compare it with the JAMSTEC forecast because JAMSTEC was slow in posting this month. What we published is complete with respect to NOAA but is missing the comparison with the forecast from another highly respected Meteorological Agency. Such comparisons can be very enlightening. This evening, JAMSTEC posted all of their forecast except for the short discussion that they usually post a few days later. It is clear that the difference between their view of the future and NOAA has not changed very much in that NOAA is forecasting ENSO Neutral with a cool bias bordering on a La Nina and JAMSTEC is still forecasting ENSO Neutral with a warm bias but less so than last month.
We can not process the JAMSTEC maps immediately, especially since the August 21, 2017 Weekly Weather Report is in the process of being finalized. But we thought it important to alert everyone that there is a disagreement on the short-term ENSO situation and actually also the ENSO situation going all the way into 2019. In this addition to the update (posted last night), we will show the old and new JAMSTEC Nino 3.4 forecast and include what we published last night with some very brief clarifying comments. The full analysis of the JAMSTEC forecast will appear later in the week.
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Here is the July 1 and Aug 1 JAMSTEC Nino 3.4 forecasts side by side with the older forecast on the left and newly issued forecast on the right.
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In this Update, we normally 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. At the time we published, we only had the NOAA forecast maps. Rather than delay providing you that information until we had the JAMSTEC information we decided to present the NOAA information and republish this report when we have the JAMSTEC information.
Some Housekeeping Issues.
The next Regular Weekly Weather and Climate Report will be published on August 21. 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.
What is shown for JAMSTEC is their maps issued with respect to their July 1 Nino 3.4 Forecast. We expect those maps to change dramatical when JAMSTEC updates their web site. So for now they are placeholders.
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 and Comparison with JAMSTEC
NOAA issued their updated Seasonal Outlook on the third Thursday of the month i.e. August 17, 2017 as is their normal schedule. JAMSTEC as of tonight has not updated their website. In this report we first take a look at the NOAA maps. We will follow our usual procedure tonight with respect to reviewing the new Update from NOAA. Then, normally, we compare the NOAA Maps to those issued by JAMSTEC. We are not able to do that tonight but will either update or republish this report when we have the JAMSTEC maps. .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.
Focus on the NOAA Update
First we will take a look at the Early Outlook for September 2017. It is called the Early Outlook because it will be updated at the end of August. Only the September 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 July 20, NOAA Report to compare against. And August is not over so we can not really compare the September forecast against August actual. It is probably best to just try to understand what NOAA is trying to convey about September which can be summarized as for temperature warm for Alaska and the Western third of CONUS and along the Atlantic Coast and Gulf Coast but EC in between with a small cool area centered on Kansas and for precipitation wet only for North and Southwest Alaska and about a third of CONUS east of a line running from Amarillo Texas to Isle Royale but not including Florida or the extreme New England.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. September/October/November is shown as SON. You will see such abbreviations often in this report.
Prior Temperature Outlook for SON 2017
New Temperature Outlook for SON 2017
Prior Precipitation Outlook for SON 2017
New Precipitation Outlook for SON 2017
Now let us focus on the long-term situation and compare the new set of maps with the maps issued on July 20, 2017.
Prior 14 Month Temperature Outlook: SON 2017 – ASO 2018
New 14 Month Temperature Outlook: OND 2017 – SON 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: SON 2017 – ASO 2018
Now Precipitation
New 14 Month Precipitation Outlook: OND 2017 – SON 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 September Outlook from the three-month Outlook and create the Outlook for the last two months in the three-month period namely October and November 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 August 17, 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. DURING THE PAST 1-2 WEEKS, THERE HAS BEEN A MODEST (BUT STILL NOTICEABLE) COOLING OF THE OCEAN SURFACE, ESPECIALLY EAST OF THE DATE LINE. NEAR TO ABOVE-NORMAL SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE BEEN REPLACED BY NEAR TO BELOW-NORMAL SST ANOMALIES. SUBSURFACE TEMPERATURE OBSERVATIONS OVER THE CENTRAL AND EASTERN EQUATORIAL PACIFIC REVEAL A LARGE RESERVOIR OF UNSEASONABLY COLD WATER FROM ABOUT 50-175 METERS BELOW THE SURFACE. THE PRESENCE OF THIS FEATURE DOES NOT SUPPORT THE DEVELOPMENT OF AN EL NINO ANY TIME SOON. IF THIS SUBSURFACE RESERVOIR OF RELATIVELY COLD WATER PERSISTS AND INTENSIFIES, THE ODDS OF A LA NINA BY WINTER WILL CORRESPONDINGLY INCREASE. ANOTHER IMPORTANT INDICATOR IS THE UPPER-OCEAN (TOP 300 METERS) HEAT CONTENT (UOHC), WHICH CONSIDERS THE POTENTIAL HEAT ENERGY AVAILABLE WITHIN A VOLUME OF SEAWATER THAT RUNS FROM THE DATE LINE EASTWARD TO 100W LONGITUDE, AND FROM 5S-5N LATITUDE. SINCE THE START OF THIS YEAR, POSITIVE UPPER-OCEAN HEAT ANOMALIES HAVE DOMINATED, BUT IN JUST THE PAST FEW WEEKS, THE HEAT ANOMALIES HAVE REVERSED SIGN, IMPLYING AN OVERALL COOLING OF THIS VOLUME OF WATER. THIS VOLUME INCLUDES THE NINO 3.4 REGION (170W-120W, 5S-5N), WHICH HAS A SIGNIFICANT IMPACT ON THE CLIMATE OF THE UNITED STATES THROUGH TROPICAL-EXTRATROPICAL INTERACTIONS. OUTGOING LONGWAVE RADIATION (OLR) ANOMALIES, USED AS A PROXY FOR THE DISTRIBUTION AND INTENSITY OF TROPICAL CONVECTION REVEAL NEAR-AVERAGE CONVECTION OVER THE EASTERN HALF OF THE PACIFIC, AND ENHANCED CONVECTION OVER THE WESTERN PACIFIC AND MARITIME CONTINENT DURING MOST OF JULY AND EARLY AUGUST. DURING THIS SAME PERIOD, THE LOW-LEVEL (850-HPA) AND UPPER-LEVEL (200-HPA) WIND ANOMALIES HAVE BEEN NEAR-AVERAGE. OVERALL, THE OCEAN AND ATMOSPHERE SYSTEM REMAINS CONSISTENT WITH ENSO-NEUTRAL CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
MOST MODELS IN THE NATIONAL MULTI-MODEL ENSEMBLE (NMME) AND THE INTERNATIONAL MULTI-MODEL ENSEMBLE (IMME) PREDICT A CONTINUATION OF ENSO-NEUTRAL CONDITIONS THROUGHOUT BOREAL AUTUMN AND INTO WINTER 2017/18, WITH SOME FAVORING A BORDERLINE NEUTRAL/LA NINA EVENT. THE NCEP CFS FORECAST PLUME DEPICTS CONSIDERABLE DISPERSION AMONG ITS ENSEMBLE MEMBERS, WITH PREDICTED NINO 3.4 SST ANOMALIES RANGING FROM ABOUT -1.5C TO +1.0C. THE ENSEMBLE MEAN DECLINES DURING THE NEXT FEW SEASONS, REACHING A PREDICTED MINIMUM NEAR -0.7C (WEAK LA NINA) DURING NDJ AND DJF 2017/18, THEN RECOVERING TO NEAR ZERO IN FMA 2018. THE CPC NINO 3.4 SST CONSOLIDATION OF THE CFS AND SEVERAL STATISTICAL FORECASTS INDICATES PERSISTENCE OF ENSO-NEUTRAL CONDITIONS IS MOST LIKELY AT LEAST INTO NEXT SPRING. THE CPC-IRI PROBABILISTIC ENSO FORECAST INDICATES AN 85-PERCENT CHANCE OF ENSO-NEUTRAL CONDITIONS CONTINUING THROUGH SEPTEMBER 2017, WITH THE PROBABILITIES GRADUALLY DECREASING TO ABOUT 55-PERCENT BY DJF 2017/18. THE ODDS OF A LA NINA INCREASE FAIRLY RAPIDLY FROM ABOUT 5-PERCENT IN SEPTEMBER TO A PEAK OF ABOUT 28-PERCENT BY DJF 2017/18, BEFORE GRADUALLY DECLINING. THE ODDS OF AN EL NINO SLOWLY INCREASE FROM ABOUT 10-PERCENT IN SEPTEMBER TO A PEAK NEAR 20-PERCENT BY MAM 2018.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
DYNAMICAL MODELS PROVIDE THE PRIMARY GUIDANCE FOR THE SEASONAL OUTLOOKS THROUGH JFM 2018, WITH DECADAL TEMPERATURE AND PRECIPITATION TRENDS PROVIDING THE PRIMARY GUIDANCE FOR LONGER LEADS. THE CALIBRATED PROBABILITY FORECASTS FROM THE NMME AND ANOMALY FORECASTS FROM ITS INDIVIDUAL MODELS, INCLUDING THE NCEP CFS, WERE USED THROUGH JFM 2018. THE DECREASING LIKELIHOOD OF EL NINO DEVELOPMENT COMPARED TO PREVIOUS OUTLOOKS, AND THE LATEST INDICATIONS FAVORING A BORDERLINE NEUTRAL/LA NINA EVENT, LED TO ADJUSTMENTS IN THE OUTLOOKS, ESPECIALLY FOR THE WINTER SEASONS. ADDITIONAL REFINEMENTS TO THE FORECAST WILL UNDOUBTEDLY BE NEEDED DURING THE NEXT FEW SEASONS, AS THE ENSO SITUATION BECOMES MORE CLEAR.
30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2017
THE SEPTEMBER 2017 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL MODEL GUIDANCE, STATISTICAL TOOLS, AND TO A LESSER EXTENT, SOIL MOISTURE ANOMALIES. 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) WAS ACTIVE DURING THE SECOND HALF OF JULY AND INTO VERY EARLY AUGUST, BUT HAS WEAKENED OVER THE PAST COUPLE OF WEEKS. THE LATEST DYNAMICAL MODEL GUIDANCE SUGGESTS THAT A MORE COHERENT SIGNAL MIGHT EMERGE OVER THE INDIAN OCEAN OVER THE NEXT WEEK OR TWO. WHILE THIS MAY PLAY A ROLE IN MODULATING TROPICAL CYCLONE ACTIVITY DURING OVER THE COURSE OF THE COMING WEEKS, THERE IS LITTLE TO BE HARVESTED IN TERMS OF TEMPERATURE AND PRECIPITATION PREDICTION FOR SEPTEMBER 2017.
THE LATEST RUNS OF THE CFS, AS WELL AS WEEK 3-4 GUIDANCE FROM THE ECMWF, DEPICT A REASONABLY HIGH AMPLITUDE TROUGH-RIDGE-TROUGH PATTERN EXTENDING FROM THE NORTHEASTERN PACIFIC THROUGH EAST-CENTRAL NORTH AMERICA AT LEAST THROUGH MID-SEPTEMBER. THIS PATTERN IS LARGELY CONSISTENT WITH THE LOW-FREQUENCY PATTERN OBSERVED OVER NORTH AMERICA OVER THE PAST 45-90 DAYS. SUCH A PATTERN FAVORS ABOVE-NORMAL TEMPERATURES OVER ALASKA AND MUCH OF THE WESTERN CONUS, AS WELL AS OVER PARTS OF THE NORTHEAST AND THE IMMEDIATE EASTERN SEABOARD AND GULF COAST REGION. THOSE LATEST DYNAMICAL TOOLS FAVOR BELOW-NORMAL TEMPERATURES OVER MUCH OF THE SOUTH-CENTRAL AND INTERIOR SOUTHEASTERN CONUS. THE DYNAMICAL TOOLS THAT WERE INITIALIZED EARLY IN THE MONTH FAVOR THE SAME GENERAL PATTERN, BUT WITH REDUCED PROBABILITIES FOR BELOW-NORMAL TEMPERATURES OVER PARTS OF THE SOUTHEASTERN AND SOUTH-CENTRAL U.S. SOIL MOISTURE DECREASES IN IMPORTANCE AS A LAGGED PREDICTOR OVER THE SOUTH-CENTRAL CONUS FROM AUGUST THROUGH OCTOBER. SOME MODEST COOLING EFFECT IS POSSIBLE WHERE POSITIVE SOIL MOISTURE ANOMALIES ARE THE GREATEST FOR PARTS OF THE CENTRAL AND SOUTHERN U.S., ESPECIALLY THROUGH THE FIRST HALF OF SEPTEMBER.
Temperature
THE TEMPERATURE FORECAST IS BASED LARGELY ON THE CALIBRATED NMME GUIDANCE, BUT TWEAKED TOWARD THE LATEST DYNAMICAL GUIDANCE THAT FAVORS A CONTINUATION OF THE WARM SEASON LOW-FREQUENCY PATTERN INTO AT LEAST THE FIRST HALF OF SEPTEMBER. THIS LEADS TO A LOW AMPLITUDE TWO-CATEGORY CHANGE OVER CENTRAL CONUS, WHERE BELOW-NORMAL TEMPERATURES ARE SLIGHTLY FAVORED DURING SEPTEMBER AND ABOVE-NORMAL TEMPERATURES ARE SLIGHTLY FAVORED FOR THE SEP-OCT-NOV SEASON. THE LOW-FREQUENCY TREND SIGNAL IS MORE LIKELY TO EMERGE IN OCTOBER AND NOVEMBER AS WE UNDERGO SEASONAL TRANSITION. OVER ALASKA, THE GREATEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE ALONG COASTAL REGIONS, WHERE WARMER-THAN-NORMAL SSTS ARE LIKELY TO HAVE SOME INFLUENCE ALONG WITH ANOMALOUSLY LOW SEA ICE EXTENT.
Precipitation
THE PRECIPITATION OUTLOOK FOR SEPTEMBER HAS LIMITED COVERAGE GIVEN THE GENERALLY POOR SKILL AT THESE LEAD TIMES THIS TIME OF YEAR. THE CALIBRATED NMME OUTLOOK IS USED AS A STARTING POINT, WITH THE COVERAGE OF PROBABILITIES FAVORING ABOVE-NORMAL RAINFALL ADJUSTED TO ALIGN WITH THE REGION FORECAST TO BE JUST EAST OF THE FORECAST ANOMALOUS TROUGH AXIS. THERE IS SOME REASON TO FAVOR BELOW-NORMAL PRECIPITATION OVER PARTS OF THE NORTH-CENTRAL AND NORTHWESTERN CONUS GIVEN THE LOW-FREQUENCY PATTERN AND THE FORECAST CIRCULATION PATTERN THROUGH MID-SEPTEMBER (DISCUSSED ABOVE). HOWEVER, FORECAST TOOLS THAT WERE INITIALIZED EARLIER, FOR WHICH INITIAL ATMOSPHERIC CONDITIONS ARE LESS IMPORTANT, SHOW LARGE UNCERTAINTY OVER THOSE REGIONS. GIVEN THE SIGNIFICANCE OF THE ONGOING DROUGHT OVER PARTS OF THE NORTH-CENTRAL U.S., THIS AREA WILL BE MONITORED CLOSELY FOR THE UPDATED OUTLOOK ISSUED ON AUGUST 31. OVER ALASKA, THE TOOLS WERE IN REASONABLY GOOD AGREEMENT FAVORING ABOVE-NORMAL PRECIPITATION ALONG THE SOUTHERN COAST, WHICH IS ALSO CONSISTENT WITH THE FORECAST CIRCULATION PATTERN. THE CALIBRATED NMME FAVORS ABOVE-NORMAL PRECIPITATION FOR THE NORTH SLOPE, CONSISTED WITH FORECAST ABOVE-NORMAL TEMPERATURES AND INCREASED MOISTURE AVAILABILITY.
Three Month: September/October/November (there is additional information on SON in the extended outlook below this section)
Temperature
THE SEPTEMBER-OCTOBER-NOVEMBER (SON) 2017 TEMPERATURE OUTLOOK INDICATES INCREASED CHANCES OF ABOVE-NORMAL TEMPERATURES ACROSS ALASKA AND THE CONTIGUOUS U.S. THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR PARTS OF THE SOUTHWEST, THE NORTHEAST, AND CENTRAL AND SOUTHERN FLORIDA (ALL AT OR ABOVE 50-PERCENT) AND THE NORTH SLOPE OF ALASKA (AT OR ABOVE 70-PERCENT).
Precipitation
THE SON 2017 PRECIPITATION OUTLOOK FAVORS ABOVE-NORMAL PRECIPITATION OVER AN AREA WHICH INCLUDES THE SOUTH-CENTRAL CONUS, THE SOUTHERN HALF OF THE MISSISSIPPI VALLEY, MOST OF THE TENNESSEE VALLEY, AND PORTIONS OF THE SOUTHEAST. ABOVE-NORMAL PRECIPITATION IS ALSO SLIGHTLY FAVORED OVER SOUTH-CENTRAL ALASKA.
PROGNOSTIC DISCUSSION OF OUTLOOKS – SON 2017 TO SON 2018
TEMPERATURE
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS THE ENTIRE FORECAST DOMAIN FOR THE SON AND OND 2017 OUTLOOKS, AS INDICATED BY A CONSENSUS OF MODELS FROM THE NMME, DRIVEN SOMEWHAT BY DECADAL TEMPERATURE TRENDS. ACROSS THE CONTIGUOUS U.S. (CONUS), THE HIGHEST PROBABILITIES (50-59 PERCENT) ARE PREDICTED FROM FAR SOUTHERN CALIFORNIA ACROSS MUCH OF THE SOUTHWEST AND INTO THE CENTRAL ROCKIES, THE NORTHEAST, AND THE FLORIDA PENINSULA, BASED ON A GENERAL CONSENSUS OF TOOLS/MODELS SUCH AS THE NMME PROBABILISTIC ANOMALY CALIBRATION (PAC), UPDATED OPTIMAL CLIMATE NORMALS (OCN), THE IMME, AND TO A LESSER EXTENT THE CFS. THE INCREASED ODDS OF ABOVE-NORMAL TEMPERATURES IN FAR SOUTHERN CALIFORNIA IS ASSOCIATED WITH RELATIVELY MILD SSTS. THE LOWER FREQUENCY COOL SIGNAL THAT HAS DOMINATED MUCH OF THE PLAINS REGION DURING THE PAST FEW MONTHS IS EXPECTED TO GIVE WAY THROUGHOUT THE SON SEASON TO WARMER LONG-TERM TRENDS. THIS IS WHY THE MONTHLY TEMPERATURE OUTLOOK FOR SEPTEMBER (WHICH DEPICTS A WEAK COOL SIGNAL OVER THE CENTRAL PLAINS) DOES NOT CONFLICT WITH THE SEASONAL TEMPERATURE OUTLOOK FOR SON (WHICH DEPICTS A WEAK WARM SIGNAL OVER THIS SAME REGION). A WIDESPREAD REGION OF MODESTLY ABOVE-NORMAL TEMPERATURES IS FAVORED OVER MANY AREAS EAST OF THE CONTINENTAL DIVIDE, INDICATED BY THE NMME PAC, CFS, AND TO A LESSER DEGREE, THE CONSTRUCTED ANALOG ON SSTS (CA-SST). IN ALASKA, ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS THE ENTIRE STATE, AS FORECAST BY ALMOST ALL DYNAMICAL MODELS, AND BY SIGNIFICANT DECADAL TEMPERATURE TRENDS. AN EXPECTED LACK, OR DELAYED ONSET, OF SEA ICE ELEVATES CHANCES FOR ABOVE-NORMAL TEMPERATURES ACROSS FAR NORTHERN ALASKA TO AT LEAST 70-PERCENT DURING THE AUTUMN, WHILE UNSEASONABLY WARM SSTS CURRENTLY SURROUNDING MOST OF THE STATE CONTRIBUTE TOWARDS THE FORECAST PROBABILITIES OF AT LEAST 60-PERCENT FOR ABOVE-NORMAL TEMPERATURES. DURING OND AND NDJ, ABOVE-NORMAL TEMPERATURES ARE FAVORED OVER NEARLY ALL OF THE CONUS, THOUGH WITH REDUCED PROBABILITIES FOR UPPER-TERCILE TEMPERATURES PREDICTED OVER PORTIONS OF THE NORTH-CENTRAL AND SOUTHEASTERN CONUS, AS SUPPORTED BY THE NMME PAC AND CONSOLIDATION (CON) TOOLS. DURING DJF 2017/18 AND JFM 2018, A BROAD AREA OF EQUAL CHANCES (EC) IS GRADUALLY CARVED OUT ACROSS THE NORTH-CENTRAL, GREAT LAKES, AND NORTHEAST REGIONS, SUPPORTED BY THE NMME PAC, AND TO SOME DEGREE, THE NCAR MODEL.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS THE WESTERN AND SOUTHERN CONUS DURING THESE TWO SEASONS, LARGELY ATTRIBUTED TO DYNAMICAL MODEL GUIDANCE AND DECADAL TEMPERATURE TRENDS. FOR THE SUBSEQUENT SEASONS, FMA TO SON 2018, THE TEMPERATURE OUTLOOKS ARE PRIMARILY BASED ON DECADAL TEMPERATURE TRENDS. PROBABILITIES FOR UPPER-TERCILE TEMPERATURES INCREASE TO 40-49 PERCENT OVER THE EASTERN CONUS DURING AMJ TO JAS 2018, AND TOP OUT OVER 50-PERCENT FOR THE FINAL THREE SEASONS (JAS TO SON 2018) ACROSS THE NORTHEAST, AND PARTS OF THE GULF COAST REGION. IN ALASKA, TRENDS FAVOR ABOVE-NORMAL TEMPERATURES FOR ALL LEADS. FROM AMJ TO SON 2018, THE PROBABILITIES FOR UPPER-TERCILE TEMPERATURES INCREASE ACROSS THE NORTH SLOPE REGION, RELATED TO THE EXPECTATION OF EARLY BREAKUP AND MELTING OF SEA ICE.
PRECIPITATION
ABOVE-NORMAL PRECIPITATION IS FAVORED FROM THE SOUTHERN GREAT PLAINS EASTWARD ACROSS THE LOWER HALF OF THE MISSISSIPPI VALLEY, MOST OF THE TENNESSEE VALLEY, AND MUCH OF THE SOUTHEAST. THIS HAS THE GENERAL SUPPORT OF THE CFS, THE NMME PAC, THE IMME, AND THE SST-CA. COMPARED TO THE PREVIOUS OUTLOOK ISSUED LAST MONTH (FOR THE SON SEASON), THE FORECAST EXPANSION OF ABOVE-NORMAL PRECIPITATION INTO THE SOUTHEAST (INCLUDING ALL OF FLORIDA) WAS INDICATED PRIMARILY BY THE SST-CA TOOL. THIS SAME TOOL ALSO PROVIDED MUCH OF THE JUSTIFICATION FOR THE PREDICTION OF ABOVE-NORMAL PRECIPITATION ACROSS SOUTH-CENTRAL PORTIONS OF ALASKA DURING SON AND OND. FOR THE OND THROUGH DJF SEASONS, THE AREA FAVORED TO RECEIVE UPPER-TERCILE PRECIPITATION INDICATED ON THE LEAD 1 MAP [Editor’s Note: This refers to the first three-month period period namely SON 2017] IS FORECAST TO SHIFT WESTWARD AND NORTHWESTWARD ACROSS THE CENTRAL AND SOUTHERN PLAINS, EVENTUALLY BECOMING FOCUSED OVER THE CENTRAL ROCKIES AND CENTRAL INTERMOUNTAIN REGION BY DJF 2017/18. THIS IS BASED PRIMARILY ON THE CFS, NMME PAC, SST-CA, AND CCA. WITH THE EXCEPTION OF THE CCA, THESE MODELS/TOOLS ALSO FORM THE BASIS FOR FAVORED DRYNESS (ALONG WITH THE IMME) ACROSS THE GULF COAST REGION DURING DJF 2017/18 AND JFM 2018. FROM FMA TO SON 2018, THE PRECIPITATION OUTLOOKS ARE BASED PRIMARILY ON PRECIPITATION TRENDS AS INDICATED BY THE CON TOOL. FOR THE FMA AND MAM 2018 SEASONS, LOWER-TERCILE PRECIPITATION IS FAVORED OVER THE SOUTHWEST. FROM MAM TO ASO 2018, UPPER-TERCILE PRECIPITATION IS FAVORED, INITIALLY ACROSS THE DAKOTAS AND UPPER MISSISSIPPI VALLEY, SHIFTING EASTWARD ACROSS THE GREAT LAKES AND NORTHEAST, AND THEN SOUTHWARD ACROSS THE ATLANTIC COAST. THIS WEAK WET SIGNAL VIRTUALLY DISAPPEARS FROM THE CON BY SON 2018, RESULTING IN AN EC FORECAST FOR THE UNITED STATES DURING LEAD 13 [Editor’s Note: This refers to the thirteenth three-month period period namely SON 2018 ].
Forecasting the Evolution of ENSO
Here is the JAMSTEC August 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. We should have an updated discussion soon and that will be reported on either when we do the JAMSTEC/NOAA comparison or in the subsequent Weekly Report. The JAMSTEC discussion is always brief and really if you look at their maps you see visually what is described in words in their discussion. I am leaving this discussion in our update-update report as the change in the JAMSTEC forecast for Nino 3.4 is not that large of a change so the prior discussion may still have some value.
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.
Below 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 August 18, 2017 fully model-based report on the right and the earlier August 10 less formal mostly based on a Meteorologist survey on the left.
This is another way of looking at it.
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 Technical ENSO Update
Published: August 18, 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-August 2017, the NINO3.4 SST anomaly was in the middle of the ENSO-neutral category. For July the SST anomaly was 0.39 C, toward the warm side of ENSO-neutral, and for May-July it was 0.47 C, in the far 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 had cooled to -0.2, in the lower half of the ENSO-neutral range. The pertinent atmospheric variables, including the upper and lower level zonal wind anomalies, have been showing mainly neutral patterns. The Southern Oscillation Index (SOI) and the equatorial SOI have been near to somewhat above average. Subsurface temperature anomalies across the eastern equatorial Pacific have declined to become just slightly below average. The combination of the SST and the atmospheric conditions clearly warrants an ENSO-neutral diagnosis.
Expected Conditions
What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued approximately one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it stated that ENSO-neutral has the greatest chance of prevailing through fall and into winter, with markedly lower chances for El Niño or La Niña development. The latest set of model ENSO predictions, from mid-August, 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 August-October through the rest of 2017, and show a likelihood of only 25% or less for El Niño development and for La Niña development through the period.
As of mid-August, at least 78% of the dynamical or statistical models predicts neutral ENSO conditions from the initial Aug-Oct 2017 season through the final Apr-Jun 2018 season. During this period, less than 10% of models predict El Niño conditions except for the final March-May and Apr-June 2018 seasons, when the percentage of models increases to about 20%. During this period, up to about 15% of models predict La Niña conditions, maximizing in the Dec-Feb season. 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 Nov-Jan 2017-18 season, among models that do use subsurface temperature information, 84% of models predicts neutral conditions, 11% predicts La Niña conditions, and 5% predicts El Niño conditions. These are similar percentages to those using all models, and the similarity persists also for longer lead target periods.
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 low throughout the forecast period, maximizing at about 25% during the Oct-Dec 2017 through Dec-Feb seasons. Similarly the chances for El Niño are low throughout, hovering just over 20% for fall 2017 and winter 2017-18, then rising to just over 30% by late spring 2018. Probabilities for ENSO-neutral are more than 80% for Aug-Oct, dropping to about 55% from Oct-Dec to Dec-Feb, and rising to about 65% for the final seasons of Feb-Apr through Apr-Jun 2018. Again, neutral is the clearly favored outcome. 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 or La Niña less than one-half those for neutral throughout. 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 judgement in combination with the model guidance. [Editors’s note: It may be that this last sentence may be artifact or perhaps should say in early September]
A look at the subsurface along the Equator is very useful.
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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 but this copy is frozen)
Discussion Issued August 16, 2017
ENSO neutral likely for the remainder of 2017
The El Niño—Southern Oscillation (ENSO) is currently neutral. All [Editor’s Note: eight] of the international climate models surveyed by the Bureau suggest the tropical Pacific Ocean is likely to stay ENSO neutral for the remainder of 2017.
Sea surface temperatures (SSTs) have cooled over much of the central tropical Pacific during the past four weeks, and are now close to the long-term average, and within the neutral range. The 30-day Southern Oscillation Index (SOI) also remains neutral, having steadied over the past three weeks. Other indicators of ENSO, such as cloudiness near the Date Line and trade winds are also at neutral levels.
The Indian Ocean Dipole (IOD) also remains neutral with consensus amongst climate models suggesting neutral conditions are likely to persist. Some models suggest positive IOD thresholds could be reached in the coming months but these values are unlikely to be sustained long enough to classify as a positive IOD event. Positive IOD events are typically associated with below average winter and spring rainfall over central and southern Australia.
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 July 1, 2017 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.
Comparison of the NOAA Outlook to the JAMSTEC Outlook
At this point we would begin to compare the NOAA forecast to the JAMSTEC forecast. Since JAMSTEC had not yet posted their updated forecast at the time we published Saturday evening, this comparison will have to wait until they do so and then we will publish yet another update which will include the NOAA JAMSTEC comparison.
I apologize for any confusion but we did not know that JAMSTEC would publish today and we did not want to withhold the NOAA information while waiting for JAMSTEC and it is always difficult dealing with both an Update Report and a Weekly Report and this is made more difficult if one or the other of these two agencies are late in posting.
