052  
FXUS05 KWBC 201230  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU JUL 20 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
THE AUGUST-SEPTEMBER-OCTOBER (ASO) 2017 TEMPERATURE OUTLOOK INDICATES INCREASED  
CHANCES OF ABOVE-NORMAL TEMPERATURES ACROSS ALASKA AND THE CONTIGUOUS U.S.,  
ALTHOUGH PROBABILITIES ARE REDUCED FROM PARTS OF THE SOUTHERN PLAINS TO THE  
CENTRAL MISSISSIPPI VALLEY. THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL  
TEMPERATURES ARE FORECAST FOR PARTS OF THE NORTHERN ROCKIES AND INTERMOUNTAIN  
WEST, THE GULF COAST AND ATLANTIC COASTS, THE NORTHEAST, AND WESTERN AREAS OF  
ALASKA. THE ASO 2017 PRECIPITATION OUTLOOK INDICATES AN INCREASED CHANCE FOR  
ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE SOUTHERN PLAINS, THE SOUTHWEST,  
SOUTHWESTERN ALASKA, AND THE ALEUTIAN ISLANDS.  
 
DURING THE AUTUMN AND WINTER 2017-18, THE CHANCES OF EL NINO DEVELOPMENT ARE  
LOWER COMPARED TO LAST MONTH. SINCE ENSO-NEUTRAL CONDITIONS ARE MOST LIKELY TO  
PERSIST, THE TEMPERATURE AND PRECIPITATION OUTLOOKS DURING THE COLD SEASON ARE  
BASED PRIMARILY ON DYNAMICAL MODEL GUIDANCE AND DECADAL TRENDS.  
 
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. WHILE SEA SURFACE TEMPERATURES (SSTS) ARE SLIGHTLY  
ABOVE AVERAGE IN THE EAST-CENTRAL PACIFIC OCEAN, ATMOSPHERIC CONDITIONS ARE  
REPRESENTATIVE OF ENSO-NEUTRAL CONDITIONS. THE OBSERVED WEEKLY SSTS CENTERED ON  
JULY 12 INDICATE POSITIVE SST ANOMALIES OF 0.5 TO 1 DEGREE C JUST TO THE WEST  
OF THE DATE LINE AND FROM ABOUT 170W TO 120W LONGITUDE ALONG THE EQUATOR. THE  
UPPER-OCEAN TEMPERATURE ANOMALY IS ABOVE AVERAGE ACROSS MUCH OF THE EQUATORIAL  
PACIFIC OCEAN TO A DEPTH OF 100 TO 150 METERS, THOUGH WITH WEAK ANOMALIES OF  
LESS THAN 2 DEGREES C.  
 
DESPITE WARMER-THAN-AVERAGE OCEAN TEMPERATURES ACROSS THE CENTRAL AND EASTERN  
PACIFIC SINCE MARCH, ATMOSPHERIC CONVECTIVE ANOMALIES FROM JUNE 17 TO JULY 12  
CONTINUE TO REMAIN NEAR AVERAGE FROM NEAR THE DATE LINE TO THE EASTERN TROPICAL  
PACIFIC. ENHANCED CONVECTION WAS OBSERVED ACROSS PARTS OF INDONESIA DURING THIS  
TIME PERIOD. WESTERLY ANOMALIES IN LOWER LEVEL WINDS AT 850-HPA WERE OBSERVED  
OVER THE EAST-CENTRAL TROPICAL PACIFIC, WHILE EASTERLY ANOMALIES WERE OBSERVED  
IN UPPER LEVEL 200-HPA WINDS OVER THE EASTERN PACIFIC. THESE ATMOSPHERIC  
INDICATORS ARE CONSISTENT WITH ENSO-NEUTRAL CONDITIONS.  
 
PROGNOSTIC DISCUSSION OF SST FORECASTS  
 
MOST MODELS OF THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) INDICATE A  
CONTINUATION OF ENSO-NEUTRAL CONDITIONS THROUGH THE AUTUMN, WITH SOME MODELS  
INDICATING WEAK TO MODERATE EL NINO CONDITIONS. THE NCEP CFSV2 PREDICTS  
NEAR-ZERO TEMPERATURE ANOMALIES IN THE EAST-CENTRAL TROPICAL PACIFIC OCEAN BY  
THE BEGINNING OF AUTUMN. THE CPC NINO 3.4 SST CONSOLIDATION OF THE CFS AND  
STATISTICAL FORECASTS INDICATES ELEVATED PROBABILITIES OF POSITIVE TEMPERATURE  
ANOMALIES THROUGH SON, AND A TEMPERATURE ANOMALY CLOSE TO ZERO DEGREES IS MOST  
LIKELY BY OND. THE CPC/IRI CONSENSUS FORECAST INDICATES PERSISTENCE OF  
ENSO-NEUTRAL CONDITIONS IS MOST LIKELY THROUGH FMA 2018 WITH A PROBABILITY  
GREATER THAN 50%, WHILE THE PROBABILITY OF DEVELOPMENT OF EL NINO CONDITIONS  
REMAINS ELEVATED FROM CLIMATOLOGICAL PROBABILITIES AND IS AT OR ABOVE 35%  
THROUGH OND.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
DYNAMICAL MODELS PROVIDE THE PRIMARY GUIDANCE FOR THE SEASONAL OUTLOOKS THROUGH  
DJF 2017-2018, WITH DECADAL TEMPERATURE AND PRECIPITATION TRENDS PROVIDING THE  
PRIMARY GUIDANCE FOR LONGER LEADS. THE CALIBRATED PROBABILITY FORECASTS FROM  
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND ANOMALY FORECASTS FROM ITS  
INDIVIDUAL MODELS, INCLUDING THE NCEP CFS, WERE USED THROUGH DJF 2017/2018. THE  
DECREASING LIKELIHOOD OF EL NINO DEVELOPMENT, COMPARED TO PREVIOUS OUTLOOKS LED  
TO ADJUSTMENTS IN THE OUTLOOKS, ESPECIALLY FOR THE WINTER SEASONS.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - ASO 2017 TO ASO 2018  
 
TEMPERATURE  
 
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS ALL OF THE FORECAST DOMAIN FOR THE  
ASO OUTLOOK, AS WELL AS OUTLOOKS FOR SON 2017 THROUGH NDJ 2017-2018, AS  
INDICATED BY A CONSENSUS OF MODELS FROM THE NMME, DRIVEN SOMEWHAT BY DECADAL  
TEMPERATURE TRENDS. LOWER PROBABILITIES FOR ABOVE NORMAL TEMPERATURES ARE  
INDICATED FOR ASO AND SON FROM PARTS OF TEXAS AND THE SOUTHERN PLAINS TO THE  
CENTRAL MISSISSIPPI VALLEY, DUE TO POTENTIAL MODERATION OF TEMPERATURES BY  
INCREASED SOIL MOISTURE IN RESPONSE TO PREDICTED PRECIPITATION IN THIS REGION.  
THE HIGHEST PROBABILITIES OF ABOVE NORMAL TEMPERATURES IN ASO ARE INDICATED FOR  
PARTS OF THE NORTHERN ROCKIES AND INTERMOUNTAIN WEST, AS WELL AS ALONG THE GULF  
AND ATLANTIC COASTS, AND THE NORTHEAST, WHERE DECADAL TRENDS ARE GREATER IN  
COMPARISON TO SEASONAL VARIABILITY. PROBABILITIES IN THE SOUTHWEST, WHERE  
DECADAL TRENDS ARE ALSO LARGE, ARE MODERATED BY A FORECAST FOR ABOVE MEDIAN  
PRECIPITATION AND RESULTING SURFACE-ATMOSPHERIC FEEDBACKS. PROBABILITIES FOR  
ABOVE-NORMAL TEMPERATURES ARE ALSO HIGHEST FOR PARTS OF SOUTHWESTERN, WESTERN  
AND NORTHWESTERN ALASKA, AS INDICATED BY THE PROBABILITY FORECASTS OF THE NMME,  
LARGELY RESULTING FROM DECADAL TRENDS.  
 
 
 
WITH ENSO-NEUTRAL CONDITIONS MOST LIKELY THROUGH WINTER, THE TEMPERATURE  
OUTLOOKS FROM ASO 2017 TO DJF 2017-18 ARE BASED PRIMARILY ON THE NMME  
CALIBRATED PROBABILITY FORECASTS. AN EXPECTED LACK OF SEA ICE ELEVATES CHANCES  
FOR ABOVE-NORMAL TEMPERATURES ACROSS NORTHERN ALASKA DURING THE AUTUMN. DECADAL  
TRENDS ARE USED AS GUIDANCE FOR THE TEMPERATURE OUTLOOKS AT LONGER LEADS FROM  
MAM TO ASO 2018 AND INDICATE INCREASED PROBABILITIES OF ABOVE-NORMAL  
TEMPERATURES WHERE TRENDS ARE THE LARGEST RELATIVE TO SEASONAL TEMPERATURE  
VARIABILITY.  
 
PRECIPITATION  
 
ENHANCED PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION FOR THE NORTHERN PLAINS  
DURING THE FIRST SEVERAL LEADS IN LAST MONTHS OUTLOOKS HAVE BEEN REMOVED FROM  
THE CURRENT OUTLOOKS, WHERE EQUAL CHANCES IS NOW INDICATED. THIS CHANGE IS  
BASED ON THE MOST RECENT DYNAMICAL MODEL GUIDANCE FROM THE NMME AND CFS.  
CALIBRATED PRECIPITATION PROBABILITY FORECASTS FROM THE NMME INDICATE ABOVE  
MEDIAN PRECIPITATION IS MOST LIKELY FOR PARTS OF TEXAS AND THE SOUTHERN PLAINS  
EXTENDING EASTWARD TO THE MISSISSIPPI RIVER. THIS SIGNAL CONTINUES IN THE  
OUTLOOKS FOR SON 2017 THROUGH DJF 2017-2018. A CONSENSUS OF THE DYNAMICAL  
MODELS INDICATE AN INCREASED CHANCE OF BELOW MEDIAN PRECIPITATION FOR PARTS OF  
PACIFIC NORTHWEST FOR ASO. THE AUGUST PRECIPITATION FORECASTS FROM THE MOST  
RECENT RUNS OF THE CFS AND ADDITIONAL DYNAMICAL MODEL FORECASTS FOR THE  
BEGINNING OF AUGUST CONSISTENTLY INDICATE ABOVE MEDIAN PRECIPITATION FOR AUGUST  
IN THE SOUTHWEST MONSOON REGION. AS THE MONTH OF AUGUST HAS GREATER  
PRECIPITATION IN THIS REGION THAN THE FOLLOWING MONTHS, ENHANCED PRECIPITATION  
IN AUGUST HAS AN INCREASED IMPACT ON THE TOTAL SEASONAL PRECIPITATION. ABOVE  
MEDIAN PRECIPITATION IS THEREFORE INDICATED FOR THE SOUTHWEST FOR ASO. ABOVE  
MEDIAN PRECIPITATION IS INDICATED FOR PARTS OF SOUTHERN ALASKA IN ASO 2017  
THROUGH DJF 2017-2018, AS INDICATED BY CALIBRATED PRECIPITATION PROBABILITY  
FORECASTS FROM THE NMME. DUE TO DECADAL TRENDS, ABOVE MEDIAN PRECIPITATION IS  
MOST LIKELY FOR PARTS OF THE NORTHERN PLAINS AND GREAT LAKES REGION FROM MAM TO  
MJJ 2018, AND FOR PARTS OF THE NORTHEAST FROM MJJ THROUGH ASO 2018.  
 
SINCE THE PREVIOUS OUTLOOK, THE CHANCES FOR EL NINO DEVELOPMENT DURING THE  
AUTUMN AND WINTER HAVE DECREASED. GIVEN THE LATEST ENSO FORECAST INDICATING A  
GREATER CHANCE OF ENSO-NEUTRAL CONDITIONS THROUGH THE WINTER, THE INCREASED  
CHANCES FOR BELOW MEDIAN PRECIPITATION FOR PARTS OF THE NORTHERN ROCKIES IN NDJ  
AND DJF 2017-2018 HAVE BEEN REMOVED. PRECIPITATION OUTLOOKS FROM JFM THROUGH  
FMA 2018 ARE BASED ON THE SEASONAL PRECIPITATION CONSOLIDATION FORECAST AND  
DECADAL TRENDS.  
 
FORECASTER: DAN COLLINS  
 
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 AUG 17 2017  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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