90 Day Narrative

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.
$$