890  
FXUS05 KWBC 191231  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU OCT 19 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
THE NOVEMBER-DECEMBER-JANUARY (NDJ) 2017-18 OUTLOOK FAVORS ABOVE NORMAL  
TEMPERATURES FOR THE MAJORITY OF THE FORECAST DOMAIN, INCLUDING MUCH OF ALASKA.  
THE HIGHEST PROBABILITIES FOR ELEVATED ODDS OF WARMER THAN NORMAL TEMPERATURES  
ARE LOCATED ACROSS PORTIONS OF THE SOUTHWEST AND TEXAS. DURING THE WINTER  
MONTHS THROUGH FEBRUARY-MARCH-APRIL (FMA) 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 NDJ 2017-18 PRECIPITATION OUTLOOK INDICATES INCREASED CHANCES OF ABOVE  
NORMAL PRECIPITATION FOR WESTERN AND NORTHERN ALASKA, AS WELL AS AREAS OF THE  
NORTHERN AND CENTRAL ROCKIES. DURING NDJ 2017-18, BELOW NORMAL PRECIPITATION IS  
FAVORED ALONG THE SOUTHERN TIER OF THE CONUS, EXCLUDING SOUTHERN CALIFORNIA. AS  
WE MOVE THROUGH THE WINTER SEASON, ELEVATED ODDS FOR ABOVE NORMAL PRECIPITATION  
INCREASE IN COVERAGE FOR AREAS OF THE NORTHERN PLAINS, GREAT LAKES AND OHIO  
VALLEY THROUGH JANUARY-FEBRUARY-MARCH (JFM) 2018 AND THEN SLOWLY DECREASE  
ENTERING THE CORE SPRING MONTHS.  
 
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  
 
A LA NINA WATCH CONTINUES, AS ATMOSPHERIC AND OCEANIC CONDITIONS, TAKEN IN  
TOTALITY, REMAIN CLOSEST TO ENSO-NEUTRAL CONDITIONS THROUGH EARLY OCTOBER.  
OCEANIC CONDITIONS CONTINUE TO MOVE QUITE CLOSE TO THE LA NINA STATE AS  
EQUATORIAL SEA SURFACE TEMPERATURE (SST) DEPARTURES FROM NORMAL ARE NEGATIVE TO  
A MAGNITUDE OF -0.5 DEGREES C FROM ABOUT 150W TO THE SOUTH AMERICAN COAST WITH  
A HORSESHOE OF ABOVE NORMAL SSTS TO THE NORTH AND SOUTH OF THIS REGION AND  
ACROSS THE FAR WESTERN PACIFIC (TYPICAL OF DEVELOPING/ESTABLISHED LA NINA  
CONDITIONS). 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 CENTRAL EQUATORIAL PACIFIC WHILE ENHANCED RAINFALL CONTINUES ACROSS THE  
MARITIME CONTINENT REGION. ALTHOUGH GENERALLY WEAK OVERALL, THE TRADE WINDS IN  
THE PACIFIC HAVE BEEN ENHANCED AND UPPER-LEVEL WESTERLY WIND ANOMALIES ARE  
CURRENTLY OBSERVED IN THE REGION AS WELL. AN ADDITIONAL FACTOR TO BE COGNIZANT  
OF IN THE COMING MONTH IS THE CURRENT DEVELOPING MJO WHICH HAS, AND WILL LIKELY  
CONTINUE TO, MODULATE SST, WINDS AND CONVECTION ON THE SUBSEASONAL TIME SCALE  
ACROSS THE PACIFIC BASIN AS IT PROGRESSES ACROSS THE PACIFIC TO THE WESTERN  
HEMISPHERE, AS CURRENTLY PREDICTED.  
 
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  
HOVERING AROUND THE -0.5 DEGREES C THRESHOLD, GENERALLY TAKEN AS THE BOUNDARY  
FOR WEAK LA NINA CONDITIONS. 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 HOVER AT THE -0.5 DEGREES C VALUE  
THROUGH JFM 2018 BEFORE GRADUALLY REDUCING TOWARD AN ANOMALY NEAR ZERO BY AMJ  
2018. THERE ARE CONSIDERABLE DIFFERENCES IN THE EVOLUTION OVER TIME OF THESE  
FORECASTS THIS MONTH, WITH THE CA, AS AN EXAMPLE, PREDICTING NEAR ZERO ANOMALY  
THROUGHOUT THE FORECAST PERIOD.  
 
THE NMME SUITE OF MODELS FOLLOW THIS GENERAL THEME, ALTHOUGH THE PERIOD OF THE  
MOST NEGATIVE NINO3.4 SST ANOMALIES VARIES SOMEWHAT AS THE CFS REACHES THIS  
POINT DURING DJF 2017-18 WHILE THE GFDL MODEL DOES SO DURING OND 2017. THE  
ENSEMBLE MEAN PREDICTION IS QUITE CONSISTENT WITH THE CPC NINO3.4 SST  
CONSOLIDATED FORECAST, ALTHOUGH WITH SOMEWHAT MORE NEGATIVE TEMPERATURE  
DEPARTURES - REACHING -0.7 DEGREES C DURING DECEMBER 2017 AND JANUARY 2018. THE  
VARIATION AND IN SOME CASES THE INCREASE IN NINO3.4 SST ANOMALIES AT THE START  
OF THE PREDICTIONS IS RELATED SUBSEASONAL NOISE ASSOCIATED WITH THE ONGOING MJO  
EVENT.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
THE OFFICIAL TEMPERATURE AND PRECIPITATION OUTLOOKS FOR THE SEASONS FROM NDJ  
2017-18 THROUGH FMA 2018 TOOK INTO CONSIDERATION IMPACTS OFTEN OBSERVED DURING  
LA NINA EVENTS AS THE LATEST OFFICIAL ENSO OUTLOOK AND NINO3.4 SST MODEL  
GUIDANCE CONTINUES TO INDICATE ELEVATED PROBABILITIES AS COMPARED TO  
CLIMATOLOGY FOR LA NINA CONDITIONS DURING THIS PERIOD. STATISTICAL MODEL  
FORECAST TOOLS SUCH AS REGRESSIONS ANCHORED TO THE CPC NINO3.4 SST  
CONSOLIDATION FORECAST AND THE CCA U.S. TEMPERATURE AND PRECIPITATION  
PREDICTIONS 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. THE CA U.S. TEMPERATURE  
AND PRECIPITATION PREDICTIONS WERE ONLY USED AT INTERMEDIATE AND LATER LEADS AS  
ITS ENSO FORECAST WAS VIEWED AS SOMEWHAT OF AN OUTLIER AS COMPARED TO THE  
REMAINING NINO3.4 SST GUIDANCE EARLY IN THE PERIOD.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2017 TO NDJ 2018  
 
TEMPERATURE  
 
THE UPDATED SET OF TEMPERATURE OUTLOOKS THIS MONTH DO INDICATE SOME SUBSTANTIAL  
CHANGES FROM THE PRECEDING SET OF OUTLOOKS DURING THE WINTER SEASONS PRIMARILY  
ACROSS THE NORTHERN CONUS AND SOUTHEAST AREAS OF ALASKA INCLUDING THE ALASKA  
PANHANDLE. INCREASING PROBABILITIES FOR LA NINA (AS INDICATED IN OBSERVATIONAL  
DATA AND THE MOST RECENT SET OF MODEL FORECASTS) AS WELL AS 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 NDJ  
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  
CONSTRUCTED ANALOGUE STATISTICAL TOOL AFTER ANY CONSIDERATIONS FOR RESIDUAL LA  
NINA IMPACTS ARE ANTICIPATED TO END.  
 
THE NDJ 2017-18 TEMPERATURE OUTLOOK IS LARGELY UNCHANGED FROM THE OUTLOOK  
RELEASED LAST MONTH AND DEPICTS ELEVATED ODDS FOR ABOVE NORMAL TEMPERATURES FOR  
MOST OF THE FORECAST DOMAIN. THE MAIN CHANGE WAS A DECREASE IN COVERAGE IN  
FAVORED ABOVE NORMAL TEMPERATURES FOR PORTIONS OF SOUTHERN ALASKA. AS WE EVOLVE  
THROUGH THE WINTER SEASON THROUGH FMA 2018, HOWEVER, AN ENHANCED LIKELIHOOD OF  
BELOW NORMAL TEMPERATURES IS HIGHLIGHTED FIRST FOR PORTIONS OF SOUTHEAST AREAS  
OF ALASKA INCLUDING THE PANHANDLE, THE FAR PACIFIC NORTHWEST TO THE FAR  
NORTHERN PLAINS. DURING JFM AND FMA 2018, BELOW NORMAL TEMPERATURES ARE FAVORED  
FOR AN AREA IN THE MIDWEST AND WESTERN GREAT LAKES. THE ADDITIONS ARE BASED AS  
A RESULT OF A CONVERGENCE OF TOOL SUPPORT FROM TYPICAL LA NINA IMPACTS,  
TEMPERATURE PREDICTIONS BASED ON REGRESSION WITH THE CPC NINO3.4 SST  
CONSOLIDATION PREDICTION AND LONG TERM TRENDS AS PREDICTORS AND CONSISTENT, TO  
FIRST ORDER, FORECASTS FROM SEVERAL SHORT TERM CLIMATE DYNAMICAL MODEL GUIDANCE  
FROM THE NMME PARTICIPANT MODELS AND ITS ENSEMBLE MEAN IN BOTH DETERMINISTIC  
AND CALIBRATED PROBABILISTIC FORMATS. ALSO, RECENT LONGER TERM TEMPERATURE  
TRENDS IN THE GREAT LAKES REGION AND MIDWEST, AS CHARACTERIZED BY 15 YEAR OCN  
METHODOLOGY, ARE NEGATIVE AND CONTRIBUTE TO THE OUTLOOK AS WELL.  
 
THE REMAINING OUTLOOKS FROM MJJ 2018 ONWARD THROUGH NDJ 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 NEAR GLOBAL SST BASED CONSTRUCTED ANALOGUE TOOL ALSO  
CONTRIBUTED TO THE OUTLOOKS.  
 
PRECIPITATION  
 
FOR PRECIPITATION, THE OUTLOOKS ARE TO FIRST ORDER SIMILAR TO THE SET OF  
OUTLOOKS RELEASED LAST MONTH WITH THE PRIMARY DIFFERENCE IN MOST CASES, AN  
INCREASE IN FORECAST COVERAGE AND IN SOME CASES AN INCREASE IN FORECAST  
PROBABILITIES. PROGRESSING FROM THE NDJ 2017-18 PERIOD THROUGH THE WINTER,  
ELEVATED ODDS FOR ABOVE NORMAL PRECIPITATION, INITIALLY HIGHLIGHTED IN THE  
NORTHERN ROCKIES, EXPAND IN COVERAGE TO INCLUDE PARTS OF THE NORTHERN PLAINS,  
MIDWEST, GREAT LAKES AND OHIO VALLEY. DRIER THAN AVERAGE CONDITIONS ARE FAVORED  
ACROSS THE SOUTHERN TIER OF THE CONUS WITH THE GREATEST PROBABILITIES IN DJF  
2017-18 AND JFM 2018 IN SOME AREAS OF THE SOUTHEAST. AGAIN, IN MOST PARTS OF  
THE REGIONS DEPICTED, ALTHOUGH THE PROBABILITIES ARE MODEST, FORECASTS REFLECT  
WHERE THERE IS A PREPONDERANCE OF EVIDENCE FROM BOTH STATISTICAL FORECAST  
TOOLS, DYNAMICAL MODEL OUTPUT AND IN SOME REGIONS NON-TRIVIAL LONG TERM, BOTH  
POSITIVE AND NEGATIVE, PRECIPITATION TRENDS.  
 
THE PRECIPITATION OUTLOOKS FROM AMJ 2018 ONWARD THROUGH OND 2018 WERE GENERALLY  
UNCHANGED 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.  
 
FORECASTER: JON GOTTSCHALCK  
 
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 NOV 16 2017  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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