582  
FXUS05 KWBC 171231  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU AUG 17 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
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).  
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.  
 
THE CURRENT NEUTRAL PHASE OF ENSO IS EXPECTED TO PERSIST AT LEAST INTO EARLY  
WINTER, AS THE CHANCES OF EL NINO DEVELOPMENT DURING THE NEXT FEW MONTHS HAVE  
DECREASED. ENSO-NEUTRAL IS STILL FAVORED, ALBEIT SLIGHTLY, DURING WINTER  
2017/18, THOUGH THE ODDS OF A WEAK WINTERTIME LA NINA HAVE INCREASED  
SIGNIFICANTLY SINCE LAST MONTH. AT THIS TIME, THE SET OF SEASONAL OUTLOOKS IS  
BASED ON THE EXPECTATION OF A BORDERLINE NEUTRAL/LA NINA EVENT. AS THE ENSO  
SITUATION BECOMES MORE CERTAIN OVER THE NEXT FEW MONTHS, ADJUSTMENTS WILL BE  
MADE ACCORDINGLY TO THE SEASONAL OUTLOOKS.  
 
EQUAL CHANCES (EC) ARE FORECAST OVER AREAS WHERE PROBABILITIES OF ABOVE-,  
BELOW-, OR NEAR-NORMAL SEASONAL MEAN TEMPERATURES AND SEASONAL ACCUMULATED  
PRECIPITATION AMOUNTS ARE EXPECTED 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  
 
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BEEN REPLACED BY NEAR TO BELOW-NORMAL SST ANOMALIES.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.  
 
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 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.  
 
FORECASTER: ANTHONY ARTUSA  
 
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 SEP 21 2017  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page