Written by Sig Silber
Updated on November 22, 2017 to incorporate JAMSTEC’s discussion re their Nino 3.4 Forecast which had not been available at the time of publication.
Both NOAA and JAMSTEC believe that La Nina Conditions are present and may last through Winter and into Spring. This leads to similar but not identical forecasts for Alaska and CONUS. We compare these two forecasts and also discuss the JAMSTEC forecast for the rest of the World. The JAMSTEC Nino 3.4 forecast raises the possibility that this period of La Nina and near La Nina Conditions may continue for another year into 2019. The details on this are discussed in this report.
Please share this article – Go to very top of page, right hand side for social media buttons.
There was a La Nina last winter and it looks like another one for this winter. It is too soon to tell for sure but there is a possibility that there will be a return visit the following summer.
Here is the current November 1, 2017 JAMSTEC forecast for the Nino 3.4 Index which is the primary forecast index for the phases of ENSO namely El Nino, Neutral, and La Nina all of which depend primarily on the Sea Surface Temperature in a particular part of the Eastern Equatorial Pacific Ocean.
This report is organized into a summary that has two graphics that show the temperature and precipitation forecasts and then a lengthy discusion which is organized into three parts:
A. A full discussion of the recent NOAA Seasonal Outlook
B. An analysis of the forecasts for ENSO by NOAA and JAMSTEC and others including the Australian Bureau of Meteorology
C. A comparison between the NOAA and JAMSTEC Forecasts.
But for those who want a quick synopsis of the two forecasts, below is a 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 Winter, Spring and into Summer. 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 | |
DJF Winter 2017-2018 Temp |  |  |  |
MAM Spring 2018 Temp |  |  |  |
JJA 2018 Summer Temp |  |  |  |
Precipitation
| NOAA Alaska Plus CONUS | JAMSTEC North America | JAMSTEC Europe | |
DJF Winter 2017/2018 Precip |  |  |  |
MAM Spring 2018 Precip |  |  |  |
JJA Summer 2018 Precip |  |  |  |
A. Focus on the NOAA Update
A note about terminology; the deviations from climatology/normal are color coded but also labeled “A” for more than (above) normal and “B” for less than (below) 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. So the words “warm”, “cool”, “wet”, “dry” should be generally interpreted as being relative to climatology/normal for that location and time of year.
First we will take a look at the NOAA Early Outlook for December 2017. It is called the Early Outlook because it will be updated at the end of November. Only the December 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 December maps from the October 19, 2017 NOAA Report to compare against. And November is not over so we can not really compare the December forecast against November actual. It is probably best to just try to understand what NOAA is trying to convey about December which can be summarized as for temperature, the CONUS Southern Tier and Northern Alaska will be warm and Southern Alaska and the Panhandle and the extreme North of CONUS from the middle of Minnesota west will be cold with the rest of CONUS EC. Re precipitation, the Southern Tier of CONUS except Western Arizona and California will be dry as will Southern Alaska and the Panhandle while Northern Alaska and the CONUS Northern Tier from the Great Lakes west will be wet.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. December/January/February is shown as DJF. You will see such abbreviations often in this report.
Prior Temperature Outlook for DJF 2017-2018
New Temperature Outlook for DJF 2017-2018
Prior Precipitation Outlook for DJF 2017 – 2018
New Precipitation Outlook for DJF 2017 – 2918
Now let us focus on the long-term situation and compare the new set of maps with the maps issued on October 19, 2017.
Prior 14 Month Temperature Outlook: DJF 2017/2018 – NDJ 2018/2019
New 14 Month Temperature Outlook: JFM 2018 – DJF 2018/2019
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:
Now Precipitation
Prior 14 Month Precipitation Outlook: DJF 2017/2018 – NDJ 2018/2019
New 14 Month Precipitation Outlook: JFM 2018 – DJF 2018/2019
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 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.
Discussion
Below are excerpts (significantly reorganized and with a lot of the redundancy and discussion of methodology removed) from the Discussion released by NOAA on November 16, 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
THE LATEST ENSO DIAGNOSTIC DISCUSSION UPDATED THE LA NINA WATCH TO A LA NINA ADVISORY, AS ATMOSPHERIC AND OCEANIC CONDITIONS, TAKEN IN TOTALITY, INDICATE ONGOING LA NINA CONDITIONS. THE LATEST WEEKLY NINO 3.4 VALUE IS -1.1 C, WHILE THE OCTOBER CONTRIBUTION TO THE ONI WAS -0.53 C. OCEANIC HEAT CONTENT (OCEAN TEMPERATURES ACROSS THE PACIFIC BASIN FROM THE SURFACE TO 300 METERS DEPTH) SHOW A CONSIDERABLE RESERVOIR OF COLDER THAN NORMAL WATER, OFTEN A PRECURSOR FOR THE DEVELOPMENT OF MORE ESTABLISHED LA NINA CONDITIONS.
IN TERMS OF THE ATMOSPHERE, SUPPRESSED CONVECTION REMAINS OBSERVED ACROSS MUCH OF THE WEST-CENTRAL EQUATORIAL PACIFIC WHILE ENHANCED RAINFALL CONTINUES ACROSS THE MARITIME CONTINENT REGION. THE TRADE WINDS IN THE PACIFIC REMAIN ONLY WEAKLY ENHANCED OVER THE PAST 30 DAYS, THOUGH MORE ROBUST UPPER-LEVEL WESTERLY WIND ANOMALIES ARE CURRENTLY OBSERVED. THE MJO HAS RECENTLY WEAKENED AND IS NOT EXPECTED TO CONTRIBUTE TO STRONG FLUCTUATIONS IN WINDS AND SSTS OVER THE COMING WEEKS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THERE HAS NOT BEEN MUCH CHANGE TO PREDICTIONS OF EQUATORIAL PACIFIC SST ANOMALIES FROM LAST MONTH WITH MOST STATISTICAL AND DYNAMICAL MODEL SOLUTIONS INDICATING A WEAK LA NINA EVENT, THOUGH SOME DYNAMICAL MODEL SOLUTIONS FORECAST NINO 3.4 VALUES TO FALL BELOW -1.0 C. SPECIFICALLY, THE CPC NINO3.4 SST CONSOLIDATION, WHICH OBJECTIVELY WEIGHTS STATISTICAL GUIDANCE (CCA, CA AND MARKOV) AND THE CFS, FORECASTS THE NINO3.4 SST ANOMALY TO PEAK BETWEEN -0.6 AND -0.7 EARLY, BEFORE APPROACHING ZERO BY SPRING. RELATIVE TO LAST MONTH, THESE VARIOUS STATISTICAL AND DYNAMICAL FORECASTS ARE IN BETTER AGREEMENT WITH RESPECT TO THE OVERALL EVOLUTION, THOUGH THE SST-CA REMAINS A BIT OF AN OUTLIER IN COLD NEUTRAL TERRITORY.
THE NMME SUITE OF MODELS FOLLOW THIS GENERAL THEME, ALTHOUGH THE PERIOD OF THE MOST NEGATIVE NINO3.4 SST ANOMALIES CONTINUES TO VARY FROM MODEL TO MODEL. THE ENSEMBLE MEAN PREDICTION IS QUITE CONSISTENT WITH THE CPC NINO3.4 SST CONSOLIDATED FORECAST, ALTHOUGH WITH SOMEWHAT MORE NEGATIVE TEMPERATURE DEPARTURES REACHING -0.9 DEGREES C DURING DECEMBER 2017 AND JANUARY 2018.
THE STATUS OF ENSO DURING SUMMER 2018 AND BEYOND IS UNCERTAIN. THE OFFICIAL SST CONSOLIDATION FAVORS NEUTRAL ENSO CONDITIONS DURING SUMMER 2018, WITH A SLIGHT TILT TOWARD LA NINA IN LATE 2018.
30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2017
THE DECEMBER 2017 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL MODEL GUIDANCE, THE TYPICAL INFLUENCE ASSOCIATED WITH LA NINA, AND LONG-TERM TRENDS. DURING THE PAST MONTH, LA NINA CONDITIONS DEVELOPED AS NEGATIVE SEA SURFACE TEMPERATURE ANOMALIES CONTINUED ACROSS THE EASTERN AND CENTRAL EQUATORIAL PACIFIC ALONG WITH SUPPRESSED (ENHANCED) CONVECTION ACROSS THE CENTRAL TROPICAL PACIFIC (MARITIME CONTINENT AND PHILIPPINES). CLIMATE SIGNALS TYPICALLY ASSOCIATED WITH LA NINA WERE CONSIDERED IN MAKING THE DECEMBER 2017 OUTLOOK, GIVEN THESE CURRENT ATMOSPHERIC AND OCEANIC STATES.
A ROBUST MJO OCCURRED DURING OCTOBER, BUT IT WEAKENED SINCE THE BEGINNING OF NOVEMBER. THE DYNAMICAL MODELS INDICATE A CONTINUED WEAK OR INCOHERENT SIGNAL DURING THE NEXT TWO WEEKS. THEREFORE, THE MJO IS NOT EXPECTED TO PROVIDE ANY FORCING TO THE EXTRATROPICS. ALTHOUGH THE MJO DID NOT FACTOR INTO THE DECEMBER OUTLOOK, ITS EVOLUTION WILL BE CLOSELY MONITORED FOR THE REVISED OUTLOOK AT THE END OF THE MONTH.
THE ARCTIC OSCILLATION (AO) INDEX IS FORECAST TO BECOME LARGELY NEGATIVE DURING MID-NOVEMBER AS A BLOCKING RIDGE PERSISTS OVER THE BERING SEA WITH ANOTHER UPPER-LEVEL RIDGE BUILDING OVER THE DAVIS STRAIT. THE DURATION OF THIS NEGATIVE AO INDEX IS UNCERTAIN AND COULD BE TRANSIENT WITH MANY GFS ENSEMBLE MEMBERS INDICATING THAT THE AO INDEX BECOMES MORE NEUTRAL BY THE END OF NOVEMBER. MOST INPUTS TO THE NMME AGREE ON ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS THE EASTERN CONUS. SINCE THE ECMWF MODEL AT WEEKS 3-4 (WHICH INCLUDES DEC 1-12) INDICATES INCREASED CHANCES FOR BELOW-NORMAL TEMPERATURES ACROSS MUCH OF THE EASTERN CONUS AND GREAT LAKES, EQUAL CHANCES OF BELOW, NEAR, OR ABOVE NORMAL TEMPERATURES ARE NECESSARY FOR THESE AREAS AT THIS TIME LEAD. THE SPATIAL PATTERN OF THE TEMPERATURE FORECAST ACROSS THE WESTERN AND SOUTH-CENTRAL CONUS IS SIMILAR TO THE SEASONAL OUTLOOK SINCE LA NINA WAS A MAJOR FACTOR IN CREATING THE DECEMBER OUTLOOK, BUT THE COVERAGE OF AREAS WHERE BELOW- AND ABOVE-NORMAL TEMPERATURES ARE FAVORED IS SMALLER DUE TO UNCERTAINTY. DYNAMICAL MODELS, INCLUDING WEEKS 3-4, AND LONG-TERM TRENDS SUPPORT THE RELATIVELY HIGH ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHWESTERN CONUS.
THE PRECIPITATION OUTLOOK FOR DECEMBER IS BASED PRIMARILY ON THE CALIBRATED NMME AND IS CONSISTENT WITH LA NINA CONDITIONS AND THE DJF OUTLOOK. THE HIGHEST PROBABILITIES FOR BELOW-NORMAL PRECIPITATION ARE FORECAST ACROSS PARTS OF THE GULF COAST AND SOUTHEAST WHERE A DRY SIGNAL IS STRONG IN LA NINA COMPOSITES FOR NDJ AND PROBABILITIES ARE RELATIVELY HIGH IN THE CALIBRATED NMME. THE BROAD AREA OF ENHANCED ODDS FOR ABOVE-NORMAL PRECIPITATION FROM THE PACIFIC NORTHWEST EAST TO THE GREAT LAKES IS EITHER SUPPORTED BY LA NINA COMPOSITES OR THE CALIBRATED NMME. PROBABILITIES FOR BELOW- AND ABOVE-NORMAL PRECIPITATION ARE MODEST DUE TO LIMITED SKILL INHERENT IN A MONTHLY OUTLOOK AT THIS TIME LEAD.
THE HIGHEST ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS ALASKA ARE FORECAST FOR AREAS OF THE STATE ADJACENT TO THE BERING AND CHUKCHI SEAS WHERE SEA SURFACE TEMPERATURE ANOMALIES ARE AVERAGING AS MUCH AS 1.5 DEGREES C ABOVE NORMAL. ENHANCED ODDS FOR BELOW-NORMAL TEMPERATURES FORECAST ACROSS PARTS OF SOUTHEAST MAINLAND ALASKA AND THE ALASKA PANHANDLE ARE BASED ON THE MONTHLY CFS TEMPERATURE FORECAST. THE FAVORED AREAS OF BELOW- AND ABOVE-NORMAL PRECIPITATION ACROSS ALASKA ARE CONSISTENT WITH THE TEMPERATURE OUTLOOK AND SUPPORTED BY THE WEEKS 3-4 CFS AND ECMWF PRECIPITATION FORECASTS ALONG WITH SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
Three Months: December 2017, January and February 2018
THE DECEMBER-JANUARY-FEBRUARY (DJF) 2017-18 OUTLOOK AND SUBSEQUENT OUTLOOKS ARE HEAVILY INFLUENCED BY ONGOING LA NINA CONDITIONS THAT ARE FORECAST TO CONTINUE THROUGH LATE WINTER.
Temperature
THE DJF OUTLOOK FAVORS ABOVE-NORMAL TEMPERATURES FOR THE MAJORITY OF THE FORECAST DOMAIN, INCLUDING MUCH OF ALASKA. THE HIGHEST PROBABILITIES OF WARMER-THAN-NORMAL TEMPERATURES ARE LOCATED ACROSS PORTIONS OF THE SOUTHWEST AND TEXAS.
THE DJF 2017-18 TEMPERATURE OUTLOOK IS LARGELY UNCHANGED FROM THE OUTLOOK RELEASED LAST MONTH. THE MAIN CHANGE WAS A DECREASE IN COVERAGE IN FAVORED ABOVE-NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTH-CENTRAL U.S. AND A SLIGHT ENHANCEMENT OF PROBABILITIES FAVORING BELOW-NORMAL TEMPERATURES OVER THE NORTHERN PLAINS AND UPPER MIDWEST. THIS CHANGE IS BASED LARGELY ON STATISTICAL GUIDANCE THAT SUGGESTS THE CURRENT SST CONDITIONS OVER THE TROPICS AND NORTHERN HEMISPHERE ARE SLIGHTLY CLOSER TO THOSE PRECEDING WINTERS WITH COLDER OUTCOMES ACROSS THE NORTHERN CONUS.
Precipitation
THE DJF 2017-18 PRECIPITATION OUTLOOK INDICATES INCREASED CHANCES OF ABOVE-NORMAL PRECIPITATION FOR WESTERN AND NORTHERN ALASKA, AS WELL AS MUCH OF THE NORTHERN CONUS, CONSISTENT WITH LA NINA. THIS FOOTPRINT SLOWLY DECREASES ENTERING THE CORE SPRING MONTHS BEFORE LONG-TERM TRENDS BECOME DOMINANT DURING THE WARM SEASON.
PROGNOSTIC DISCUSSION OF OUTLOOKS – DJF 2017 TO DJF 2018 (With a focus on months beyond DJF 2017/2018)
THE OFFICIAL TEMPERATURE AND PRECIPITATION OUTLOOKS FOR THE SEASONS FROM DJF 2017-18 THROUGH FMA 2018 TOOK INTO CONSIDERATION IMPACTS OFTEN OBSERVED DURING LA NINA EVENTS AS THE LATEST OFFICIAL ENSO OUTLOOK FORECASTS LA NINA CONDITIONS TO CONTINUE THROUGH THE UPCOMING COLD SEASON. STATISTICAL FORECAST TOOLS, SUCH AS REGRESSIONS ANCHORED TO THE CPC NINO3.4 SST CONSOLIDATION FORECAST AND THE CCA, ALONG WITH DYNAMICAL MODEL GUIDANCE FROM THE NMME SUITE OF MODELS, BOTH IN DETERMINISTIC AND CALIBRATED PROBABILISTIC FORM, CONTRIBUTED HEAVILY TO THE OUTLOOK. LONG TERM TRENDS IN BOTH TEMPERATURE AND PRECIPITATION WERE ALSO UTILIZED QUITE STRONGLY IN SOME AREAS IN THE OUTLOOKS, THOUGH THESE TRENDS ARE NOT INDEPENDENT OF THE AFOREMENTIONED FORECAST TOOLS. INTERNATIONAL MODEL GUIDANCE FROM THE ECMWF, UKMET, AND JMA, ARE ALL BROADLY CONSISTENT WITH THE OFFICIAL OUTLOOKS. THE SST-CA IS UTILIZED THIS MONTH SINCE IT IS LESS OF AN OUTLIER WITH RESPECT TO ONGOING AND FORECAST TROPICAL PACIFIC SSTS.
TEMPERATURE
THE UPDATED SET OF TEMPERATURE OUTLOOKS THIS MONTH KEEP NEAR PERFECT CONTINUITY WITH THOSE ISSUED LAST MONTH, AS ONLY MINOR CHANGES WERE NEEDED. STATISTICAL AND DYNAMICAL FORECAST TOOLS THAT IN LARGE PART ARE CONSISTENT WITH TYPICAL LA NINA IMPACTS, ESPECIALLY THOSE OBSERVED IN THE MORE RECENT PORTION OF THE AVAILABLE RECORD, ARE A STRONG CONTRIBUTION TO THE TEMPERATURE OUTLOOK EVOLUTION FROM DJF 2017-18 THROUGH FMA 2018. LONG-TERM TRENDS IN MANY AREAS ALSO PLAYED A CONSIDERABLE ROLE IN THE OUTLOOK EVOLUTION AT NEARLY ALL FORECAST LEADS. OUTLOOKS FROM SUMMER 2018 WERE PRIMARILY DRIVEN BY LONG TERM TRENDS AND THE SST-CA STATISTICAL TOOL AFTER ANY CONSIDERATIONS FOR RESIDUAL LA NINA IMPACTS ARE ANTICIPATED TO END.
DURING THE WINTER MONTHS THROUGH THE MARCH-APRIL-MAY (MAM) 2018 SEASON, ENHANCED ODDS FOR BELOW-NORMAL TEMPERATURES ARE HIGHLIGHTED IN VARYING AREAS OF THE NORTHERN CONUS, SOUTHEAST ALASKA AND THE ALASKA PANHANDLE, WHILE ABOVE-NORMAL TEMPERATURES REMAIN FAVORED FOR MUCH OF THE WESTERN AND SOUTHERN CONUS, AND NORTHERN ALASKA.
AS WE EVOLVE FROM THE WINTER SEASON THROUGH MAM 2018, AN ENHANCED LIKELIHOOD OF BELOW-NORMAL TEMPERATURES REMAINS HIGHLIGHTED FOR PORTIONS OF SOUTHEAST ALASKA INCLUDING THE PANHANDLE, THE PACIFIC NORTHWEST, AND THE NORTHERN PLAINS. RECENT TEMPERATURE TRENDS IN THE GREAT LAKES REGION AND MIDWEST, AS CHARACTERIZED BY 15 YEAR OCN METHODOLOGY, ARE VERY SLIGHTLY NEGATIVE AND CONTRIBUTE TO AN OUTLOOK THAT IS COOLER THAN THE NMME ANOMALY FORECAST (AND UNCALIBRATED PROBABILITIES) FOR THAT REGION.
THE REMAINING OUTLOOKS FROM AMJ 2018 ONWARD THROUGH DJF 2018-19 ARE PRIMARILY BASED ON LONGER TERM TEMPERATURE TRENDS THAT CAN BE STRONG AND REASONABLY PREDICTABLE IN MANY AREAS OF THE CONTIGUOUS U.S. AND ALASKA. ALONG WITH TRENDS, PREDICTIONS FROM THE SST-CA ALSO CONTRIBUTED TO THE OUTLOOKS.
PRECIPITATION
FOR PRECIPITATION, THE OUTLOOKS ARE AGAIN VERY SIMILAR TO THE SET OF OUTLOOKS RELEASED LAST MONTH. IN DJF THE MINOR CHANGES INCLUDE SUBTLE INCREASES IN THE PROBABILITIES FOR ABOVE-(BELOW-)NORMAL PRECIPITATION ACROSS THE NORTHWEST (CALIFORNIA). PROBABILITIES ARE INCREASED OVER ALASKA AS WELL, WITH BELOW-NORMAL PRECIPITATION NOW FAVORED OVER THE SOUTH COAST AND PANHANDLE. INTERESTINGLY, THE CALIBRATED NMME PROBABILITIES INDICATED ENHANCED ODDS OF ABOVE-NORMAL PRECIPITATION OVER TEXAS DURING DJF, WHICH IS AT ODDS WITH STATISTICAL GUIDANCE AND THE ECMWF SEASONAL FORECAST. A SMALL REDUCTION IN PROBABILITIES FAVORING BELOW-NORMAL PRECIPITATION WAS MADE IN THAT AREA AS A RESULT OF SOMEWHAT INCREASED UNCERTAINTY. PROGRESSING FROM THE DJF 2017-18 PERIOD THROUGH THE SPRING, ELEVATED ODDS FOR ABOVE-NORMAL PRECIPITATION ACROSS THE NORTHERN CONUS, DIPPING DOWN INTO THE OHIO AND TENNESSEE VALLEYS AT TIMES, REMAIN INTACT. BELOW-NORMAL PRECIPITATION OVER THE SOUTHERN TIER OF THE U.S. IS ALSO FAVORED INTO SPRING. OVER WESTERN AND CENTRAL MAINLAND ALASKA, ABOVE-NORMAL PRECIPITATION IS NOW FAVORED THROUGH MJJ 2018 BASED ON THE LATEST DYNAMICAL AND STATISTICAL GUIDANCE.
THE PRECIPITATION OUTLOOKS FROM AMJ 2018 ONWARD THROUGH OND 2018 WERE SIMILAR FROM THE OUTLOOKS PREPARED LAST MONTH. THESE FORECASTS ARE HIGHLIGHTING GENERALLY SMALL REGIONS WHERE LONG-TERM PRECIPITATION TRENDS ARE EVIDENT AND WHERE HISTORICAL CROSS VALIDATED PREDICTION SKILL HAS BEEN SHOWN TO BE POSITIVE. PROBABILITIES FAVORING BELOW-NORMAL PRECIPITATION WERE INTRODUCED OVER PARTS OF THE INTERIOR NORTHWEST FROM MJJ THROUGH JAS 2018 BASED ON LONG-TERM TRENDS.
I have not done this before but the discussion that was issued Friday with the Week 3 and Week 4 forecast (Operational for temperature and experimental for precipitation) is quite interesting so here it is.
Week 3-4 Forecast Discussion Valid Sat Dec 02 2017-Fri Dec 15 2017
The Week 3-4 outlook this week takes place within a backdrop of ongoing La Nina conditions and after the demise of a rather substantial MJO event during October into November. La Nina ocean and atmospheric conditions serve as the low frequency base state for this outlook with no predictions of revitalized, organized MJO activity anticipated over the next 1-2 weeks. The forecast temperature and precipitation outlooks are based on low frequency La Nina background conditions, in some areas local sea surface temperature anomalies, statistical model guidance and long term trends. Dynamical model guidance also played a substantial role in the outlooks, but primarily from the ECMWF system.
The dynamical model guidance had large spread this week with all three utilized operational center model systems offering varying depictions of some of the large scale features over the Pacific Ocean and North America region. There were large changes in Week-3 forecasts from the CFS and JMA solutions across the Pacific sector than that most likely to arise out of the Week-2 period at the moment. It was viewed that the ECMWF solution for Week-3 to be the most consistent and representative with the anticipated eventual evolution over the Week 2-4 time period. Therefore, its temperature and precipitation forecast was considerably more heavily weighted in the final outlook maps.
The temperature outlook depicts elevated probabilities for above normal temperatures for northern and western areas of Alaska supported by continuing above normal sea surface temperatures, long term trends and the majority of bias corrected, calibrated dynamical model guidance. Statistical model forecast guidance incorporating information from ENSO, the MJO and long term trends favors above normal temperatures for areas across the southwest corner of the CONUS with the primary drivers being La Nina and long term trends, rather than the MJO. Dynamical model guidance especially from the ECMWF and JMA further support this area of elevated odds of anomalous warmth so probabilities are highest in this region. The enhanced likelihood of above normal temperatures extends to the north to include much of the remainder of the West as well as much of the Great Plains. This is supported by the expectation of considerable Pacific air entering the CONUS consistent with the preferred ECMWF solution and so its calibrated dynamical model guidance, but also to a lesser degree from the CFS and JMA solutions. The probabilities are lessened for the northern Plains in deference to statistical model guidance favoring below normal temperatures related to a potential La Nina influence. There exists considerable uncertainty in both statistical and dynamical model guidance across the eastern CONUS as even model output from the ECMWF is quite muted as well as in contradiction to solutions from the CFS and JMA systems. Equal chances (EC) is forecast in the eastern CONUS.
The precipitation outlook utilized a mixture of statistical model forecast guidance, some commonly observed La Nina impacts and bias corrected, calibrated dynamical model guidance. Even though at odds with typical La Nina impacts, above normal precipitation is favored for parts of the South Coast of Alaska and the Alaska Panhandle as the preferred dynamical model guidance (i.e., ECMWF), supports wetter than normal conditions in this region. The North Slope of Alaska also has an enhanced likelihood of above normal precipitation as indicated by all bias corrected, calibrated dynamical model guidance. The strong trough and somewhat zonal flow across the Pacific to the West coast of North America predicted by the ECMWF solution favors above normal precipitation for areas of the Pacific Northwest. Statistical model guidance (mainly from long term trends) favors an extension of this area to the east to include parts of the northern Rockies. A rather large area of marginally elevated probabilities for below normal precipitation is shown from the Southwest CONUS, east and north to include much of the interior portion of the country, to the Gulf Coast and Florida. A combination of factors, the La Nina low frequency base state, long term trends and the anticipated upper-level height pattern (ridge-trough) over the period across the CONUS favors in the mean an area of upper-level convergence and so generally fair surface conditions.
For Hawaii, above normal ocean surface temperatures favor elevated odds for above normal temperatures for all areas. Dynamical model guidance quite marginally favors above normal precipitation for eastern areas of the Hawaiian Islands while uncertainty in the forecast tools results in an outlook of EC for western areas.
B. An analysis of the forecasts for ENSO by NOAA and JAMSTEC and others including the Australian Bureau of Meteorology
El Nino Probabilities used by NOAA in Their Forecast (The forecast for the value of the Nino 3.4 Index receives the most attention).
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.
Here is the NOAA forecast for the Nino 3.4 Index.
I have added a blue line at -0.5C which is the level that defines La Nina Sea Surface Temperature in the Nino 3.4 Measurement Area. This level needs to be maintained or exceeded on the downside for five consecutive overlapping three-month periods to constitute a La Nina not just a period of La Nina Conditions. In the above graphic, the required duration may be barely met over the period from mid October through MAM 2018. But it does not last that long in some other models that NOAA uses. It does not last that long in many International forecasting models. So it is a judgment call at this point in time re this La Nina Condition recently declared (click here to read the Advisory) will eventually be recorded as a full La Nina.
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. Below is the October 12 and October 19 CPC/IRI ENSO Forecasts
And here is the most recent set of graphics. We had anticipated that this would have been updated last Thursday but it was not and we doubt that it would have changed very much.
Published: November 09, 2017
El Niño/Southern Oscillation (ENSO) Diagnostic Discussion issued jointly by the Climate Prediction Center/NCEP/NWS and the International Research Institute for Climate and Society
ENSO Alert System Status: La Niña Advisory
Synopsis: La Niña conditions are predicted to continue (~65-75% chance) at least through the Northern Hemisphere winter 2017-18.
During October, weak La Niña conditions emerged as reflected by below-average sea surface temperatures (SSTs) across most of the central and eastern equatorial Pacific Ocean. The weekly Niño indices were variable during the month, with values near -0.5° C during the past week in the Niño-3.4 and Niño-3 regions. Sub-surface temperatures remained below average during October reflecting the anomalously shallow depth of the thermocline across the central and eastern Pacific. Also, convection was suppressed near the International Date Line and slightly enhanced over parts of the Maritime Continent and the Philippines. Over the equatorial Pacific Ocean, low-level trade winds were mainly near average, but the upper-level winds were strongly anomalously westerly and the Southern Oscillation Index was positive. Overall, the ocean and atmosphere system reflects the onset of La Niña conditions.
For the remainder of the Northern Hemisphere fall and winter 2017-18, a weak La Niña is favored in the model averages of the IRI/CPC plume and also in the North American Multi-Model Ensemble (NMME). The consensus of forecasters is for the event to continue through approximately February-April 2018. In summary, La Niña conditions are predicted to continue (~65-75% chance) at least through the Northern Hemisphere winter.
La Niña is likely to affect temperature and precipitation across the United States during the upcoming months (the 3-month seasonal temperature and precipitation outlooks will be updated on Thursday November 16th). The outlooks generally favor above-average temperatures and below-median precipitation across the southern tier of the United States, and below-average temperatures and above-median precipitation across the northern tier of the United States.
As you can see there has been some recent change to limit the period where La Nina is favored to just the Fall and Winter. The CFS.v2 model holds the La Nina conditions for perhaps an additional two months.
Now for a more detailed look. Below is the pair of graphics that I regularly provide in my Monday night Weather and Climate Report. The date shown is the midpoint of a five-day period with that date as the center of the five-day period. The bottom graphic shows the absolute values, the upper graphic shows anomalies compared to what one might expect at this time of the year in the various areas both 130E to 90W Longitude and from the surface down to 450 meters. At different times I have discussed the difference between the actual values and the deviation of the actual values from what is defined as current climatology (which adjusts every ten years except along the Equator where it is adjusted every five years) and how both measures are useful for other purposes.
| There is cold water from 170W to Land. To the west, the cool pool is no longer quite 200 meters deep. We now have warm water developing west of the Dateline and starting to cross the Dateline. Soon it will be intruding into the Eastern Pacific Nino 3.4 Measurement Area. La Nina’s days are numbered. But that process takes a few to several months to play out. |
 |
| The 28C Isotherm is at 175W, the 27C Isotherm is at 170W, the 25C Isotherm is at 145W. |
A flattening of the Isotherm Pattern is an indication of ENSO Neutral just as a steepening of the pattern indicates La Nina or El Nino depending on where the slope shows the warm or cool pool to be. That flattening occurred to some extent after last year’s La Nina and now we have returned to a steeper pattern consistent with a weak La Nina thermocline.
Tracking the change.
 |  |
It could well be that the every ten year 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.
Here is the current November 1, 2017 JAMSTEC forecast for the Nino 3.4 Index.
There has since last month been a significant change in the JAMSTEC forecast of the Nino 3.4 Index It is now fairly consistent with the NOAA forecast but the NOAA forecast is more suggestive that this cool event will have sufficient duration to be declared a La Nina and will reach a lower level of the Nino 3.4 index. The JAMSTEC forecasted Index may not be low enough for long enough to be declared an official La Nina (-0.5C or lower) but it is close and it continues to be a negative or neutral value through the forecast period way into 2019. The fairly minor differences between the various Nino 3.4 forecasts have an impact on the seasonal outlooks of the two Agencies.
Here is the discussion from JAMSTEC: [We updated this article on November 22 with the short JAMSTEC Discussion when it was posted]
Nov. 22, 2017 Prediction from 1st Nov., 2017
ENSO forecast:
The weak La Niña-like condition will persist until boreal spring of next year. Then the tropical Pacific will return to a normal state by summer.
Indian Ocean forecast:
A normal state in the tropical Indian Ocean will persist until spring of next year. Then we expect a positive Indian Ocean Dipole in summer of 2018. 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.
Regional forecast:
On a seasonal scale, most part of the globe will experience a warmer-than-normal condition, while some parts of Africa and Brazil will experience a colder-than-normal condition in boreal winter.
As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for some parts of East Africa, eastern Southern Africa, Philippine, East Australia, and northern Brazil during boreal winter, whereas most parts of Indonesia, West Australia, West Africa, southern Europe, western U.S, eastern China and southern Brazil will experience a drier condition during boreal winter. Those are partly due to the weak La Niña-like condition.
In winter, most parts of Japan will experience warmer- and drier-than-normal conditions.
Forecasts from Other Meteorological Agencies.
Here is the Nino 3.4 report from the Australian BOM (it updates every two weeks)
POAMA, run at the Bureau of Meteorology, generates a nine-month forecast each fortnight. The most recent model run (generated 5 November) indicates NINO3.4 will just touch on La Niña thresholds during the austral summer before warming again and returning to near average values by autumn 2018.
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 based on their criteria through their forecast period. But it would meet the NOAA criteria for La Nina Conditions but it is marginal for having sufficient duration.
Indian Ocean IOD (It updates every two weeks)
The IOD Forecast is indirectly related to ENSO but in a complex way.
Discussion Issued November 5
The IOD is currently neutral with the weekly IOD index value (to 5 November) at –0.1 °C.
All six models favour a neutral IOD for the rest of 2017 and early 2018.
Indian Ocean Dipole events are typically unable to form between December to April. This is because the monsoon trough shifts south over the tropical Indian Ocean changing wind patterns, which prevents the IOD pattern from being able to form. It has little effect on Australian climate at this time of year.
Does the Atmosphere as measured by the SOI Index confirm that we have La Nina Conditions?
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 suggest that we are entering La Nina “Conditions”. NOAA has declared that La Nina Conditions currently exist.
The SOI Index is quite volatile. So even + or – 7.0 is not that significant. + or – 20 means something.
 |
 |
C. Now we begin our comparison of the NOAA and JAMSTEC Forecasts (Focus on next nine months i.e. three seasons)
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.
JAMSTEC works in three-month intervals which correspond to seasons and does not change the selection of months each time they update but does so every three months. At that time they drop one season and add another season further in the future. So for JAMSTEC we have Winter (DJF 2017-2018) Spring (MAM 2018) and Summer (JJA) to work with and we have the corresponding maps from NOAA so that we can compare the two. 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 Europe including parts of North Africa and Western Asia from the Worldwide JAMSTEC maps and include it in the summary table at the beginning of this article.
DJF 2017/2018 (Winter)
Temperature
NOAA
And here is the DJF 2017/2018 temperature forecast for North America that I extracted from the JAMSTEC World Forecast
And now the JAMSTEC WORLD FORECAST (for this graphic my comments are mostly related to areas other than Alaska and CONUS as those comments appear with the graphics above)
Precipitation
NOAA
And here is the DJF 2017/2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast.
JAMSTEC WORLD FORECAST
Here is the precipitation forecast from Queensland Australia. It does not cover the same months but rather NDJ 2017-2018:
It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. In this graphic, CONUS looks like a north south divide with the southern tier dry which pretty much agrees with both NOAA and JAMSTEC. Southern Africa is wet. Eastern Australia is wet, Europe is dry. This forecast will be updated on December 1 when the monthly average of the SOI for November becomes available. .
MAM (Spring)
Temperature
NOAA
And here is the MAM 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
Fairly similar and the view of Canada helps to put it in perspective. But NOAA sees the cool anomaly extending into North Central CONUS but JAMSTEC limits the cool area to further west.
JAMSTEC WORLD FORECAST
For JAMSTEC we see a lot more cool areas in this season. Northern South America is cool plus much of Central America as is Northern Australia, Northern Africa, Eastern India, Western Canada and Greenland.
Precipitation
NOAA
And here is the MAM 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
NOAA shows Northern Alaska wet but for JAMSTEC it is mostly EC. NOAA shows the Northern Tier of CONUS wet but for JAMSTEC it is mixed to dry. JAMSTEC shows the extreme Southwest dry while NOAA shows a more consistent dry pattern for the Southern Tier of CONUS but not extending as far west but also less intense for the Southeast than JAMSTEC.
JAMSTEC WORLD FORECAST
Much of Southern Africa is wet as is Southern South America. Southeast Asia is Dry. So is Southern Europe.
JJA 2018 (Summer)
Temperature
NOAA
And here is the JJA 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
The cool areas are Scandinavia, Northern Australia, Northern Canada, east of the Caspian Sea Central America and Greenland.
Precipitation
NOAA
And here is the JJA 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Conclusion
Both forecasts are based on ENSO being primarily negative with NOAA going all the way to a weak but short La Nina and JAMSTEC not quite as convinced that this will be a full La Nina. The differences in the forecast maps are again less than last month. Aside from the comparison of NOAA and JAMSTEC for Alaska and CONUS, JAMSTEC also provides a worldview that NOAA does not.
One value of doing this sort of analysis is that as the projected value of Nino 3.4 changes, we have the basis for extrapolating between these two sets of forecast maps if the Nino 3.4 forecasts come closer together. If they become farther apart, it may still be possible to make some reasonable guesses as to how this will impact weather. This approach may not be as useful this month since both NOAA and JAMSTEC have similar forecasts for Nino 3.4
Some Housekeeping Issues.
The next Regular Weekly Weather and Climate Report will be published on November 20, 2017. 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.
