853  
FXUS05 KWBC 161332  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EST THU NOV 16 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
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. 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. 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.  
 
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.  
 
EQUAL CHANCES (EC) ARE FORECAST OVER AREAS WHERE PROBABILITIES OF ABOVE-,  
BELOW-, OR NEAR-NORMAL SEASONAL MEAN TEMPERATURES AND SEASONAL ACCUMULATED  
PRECIPITATION AMOUNTS ARE FAVORED TO BE SIMILAR TO CLIMATOLOGICAL PROBABILITIES.  
 
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS  
NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE:  
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/TOOLS/BRIEFING  
 
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.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
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.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - DJF 2017 TO DJF 2018  
 
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.  
 
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. 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.  
 
FORECASTER: STEPHEN BAXTER  
 
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING  
THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3  
COMPLETE DECADES AS THE CLIMATIC REFERENCE PERIOD. THE PROBABILITY ANOMALIES  
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT  
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.  
 
FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE  
FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT  
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/LONG_RANGE/TOOLS.HTML  
(USE LOWER CASE LETTERS)  
INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT:  
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING/US/OUTLOOK/OUTLOOK.SHTM  
L  
(USE LOWERCASE LETTERS)  
NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR  
VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM  
RANGE FORECASTS SHOULD BE CONSULTED.  
 
THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT  
MONTH ON DEC 21 2017  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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