859  
FXUS05 KWBC 181230  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU MAY 18 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
THE JUNE-JULY-AUGUST (JJA) 2017 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL  
TEMPERATURES FOR MUCH OF THE FORECAST DOMAIN. FOR THE CONTIGUOUS U.S.,  
ABOVE-NORMAL SEASONAL MEAN TEMPERATURES ARE MOST LIKELY FOR THE EASTERN U.S.,  
ACROSS THE SOUTHERN STATES, AND WEST OF ROCKY MOUNTAINS. THE GREATEST ODDS ARE  
INDICATED FOR PARTS OF THE SOUTHWEST, THE GULF COAST AND ATLANTIC COASTAL  
REGIONS. ABOVE-NORMAL TEMPERATURES ARE ALSO FAVORED FOR MUCH OF ALASKA.  
 
THE JJA 2017 PRECIPITATION OUTLOOK INDICATES ENHANCED PROBABILITIES OF  
ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE ROCKIES AND HIGH PLAINS, CENTERED  
EAST OF THE CONTINENTAL DIVIDE, EXTENDING SOUTHWARD THROUGH THE SOUTHERN  
PLAINS. ABOVE-MEDIAN PRECIPITATION IS ALSO SLIGHTLY FAVORED FOR PARTS OF  
MAINLAND ALASKA.  
 
AS THE FORECAST PROGRESSES TOWARD THE COLD SEASON, A SLIGHT TILT TOWARD EL NINO  
(RELATIVE TO LA NINA) IS INDICATED BY THE LATEST OBJECTIVE GUIDANCE AND EXPERT  
ASSESSMENTS. THIS HAS A SMALL IMPACT ON THE TEMPERATURE AND PRECIPITATION  
FORECASTS FOR THE SEASONS SPANNING SON 2017 THROUGH FMA 2018.  
 
EQUAL CHANCES (EC) ARE FORECAST OVER AREAS WHERE ODDS 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 AS A WHOLE  
INDICATE ENSO-NEUTRAL CONDITIONS ARE CONTINUING. THE LATEST WEEKLY SST ANOMALY  
MAP INDICATES THAT WEAKLY POSITIVE SST ANOMALIES EXIST ACROSS NEARLY THE ENTIRE  
EQUATORIAL PACIFIC BASIN, WITH HIGHER AMPLITUDE ANOMALIES LOCATED NEAR THE  
SOUTH AMERICAN COAST. THE HEAT CONTENT ANOMALY OF THE UPPER-OCEAN LAYERS, TO A  
DEPTH OF 300 METERS, SUMMED ACROSS THE BASIN FROM THE DATE LINE TO 100W HAS  
REBOUNDED FROM THE DECREASE OBSERVED LAST MONTH AND IS NOW POSITIVE.  
 
IN THE ATMOSPHERE OVER THE PAST MONTH, LOWER TROPOSPHERIC ZONAL WIND ANOMALIES  
WERE WEAK. OVER THE SAME PERIOD, MEASUREMENTS OF TROPICAL CONVECTION INDICATED  
THE DEVELOPMENT OF ENHANCED CONVECTION JUST SOUTH OF THE EQUATOR WITH WEAKLY  
ENHANCED CONVECTION CONTINUING OVER THE MARITIME CONTINENT. THIS COMBINATION OF  
THE ATMOSPHERIC AND OCEANIC EVOLUTION SUGGESTS A SHIFT FURTHER AWAY FROM THE  
REMNANT LA NINA BASE STATE.  
 
PROGNOSTIC DISCUSSION OF SST FORECASTS  
 
THE CPC NINO 3.4 SST INDEX CONSOLIDATION FORECAST, WHICH INCLUDES CANONICAL  
CORRELATION ANALYSIS (CCA), CONSTRUCTED ANALOG (CA), AND MARKOV STATISTICAL  
FORECASTS, ALONG WITH THE CFS DYNAMICAL MODEL, PREDICTS A MEDIAN TEMPERATURE  
ANOMALY OF BETWEEN +0.4C AND +0.5C FOR THE COMING SEASONS FROM APPROXIMATELY  
JJA THROUGH NDJ 2017, WITH EL NINO AS MOST LIKELY FROM LATE SUMMER THROUGH  
AUTUMN. THE CFS HAS BACKED OFF ITS EL NINO FORECAST IN A FAIRLY DRAMATIC  
FASHION OVER THE PAST MONTH, WHILE THE CA STATISTICAL FORECAST HAS BECOME THE  
WARMEST CONSTITUENT MEMBER OF THE CONSOLIDATION FORECAST. THE LATEST FORECASTS  
FROM THE DYNAMICAL SUITE OF MODELS FROM THE NMME CONTINUE TO FAVOR EL NINO  
DEVELOPMENT, THOUGH NOT AS STRONGLY AS LAST MONTH. THE LATEST OFFICIAL ENSO  
OUTLOOK FROM CPC/IRI PLACES THE ODDS OF EL NINO AND ENSO NEUTRAL AT ROUGHLY 45%  
FROM JJA THROUGH DJF. THE CONSENSUS FORECAST INDICATES THE LIKELIHOOD OF A  
REPEAT LA NINA EVENT TO BE SMALL DURING THIS FORECAST PERIOD.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
THE PRIMARY TOOLS USED FOR THIS SET OF SEASONAL OUTLOOKS INCLUDED BOTH  
STATISTICAL AND DYNAMICAL MODEL FORECAST GUIDANCE, AND IN PARTICULAR AT LONGER  
LEADS, DECADAL TEMPERATURE AND PRECIPITATION TRENDS. THE CALIBRATED DYNAMICAL  
MODEL GUIDANCE FROM THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND, TO  
LESSER EXTENT, ITS INDIVIDUAL MODELS, INCLUDING THE NCEP CFS, WERE IMPORTANT  
CONTRIBUTORS TO THE OUTLOOKS THROUGH OND 2017. ANTECEDENT SOIL MOISTURE AND  
SNOWPACK ANOMALIES IN CERTAIN REGIONS ALSO IMPACTED THE OUTLOOKS AT EARLY  
LEADS. WHILE THE ENSO FORECAST REMAINS HIGHLY UNCERTAIN, THE SLIGHT TILT TOWARD  
EL NINO WAS CONSIDERED IN THE TEMPERATURE AND PRECIPITATION FROM SON THROUGH  
FMA.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2017 TO JJA 2018  
 
TEMPERATURE  
 
THE LATEST JJA AND JAS 2017 TEMPERATURE OUTLOOKS INDICATE ABOVE-NORMAL  
TEMPERATURES ARE MOST LIKELY FOR MUCH OF THE FORECAST DOMAIN, WITH THE  
EXCEPTION OF PARTS ROCKIES AND PLAINS. THE CHANCES OF ABOVE-NORMAL SEASONAL  
MEAN TEMPERATURES ARE SLIGHTLY ENHANCED FOR MUCH OF THE PACIFIC NORTHWEST, BUT  
THE PROBABILITY OF ABOVE-NORMAL TEMPERATURES IS MODERATED BY RECENT POSITIVE  
SNOW AND SOIL MOISTURE ANOMALIES. ABOVE-NORMAL TEMPERATURES ARE PARTICULARLY  
ENHANCED FOR A REGION STRETCHING FROM THE SOUTHWEST, EASTWARD ACROSS THE FAR  
SOUTHERN TIER OF THE CONUS INTO THE EASTERN U.S. THE GREATEST PROBABILITIES  
EXCEED 50% FOR PARTS OF THE SOUTHWEST AND ALONG THE GULF AND ATLANTIC COASTS,  
FOLLOWING THE CALIBRATED PROBABILISTIC GUIDANCE FROM THE NMME. NEGATIVE SOIL  
MOISTURE ANOMALIES IN THE SOUTHEAST REGION ALSO CONTRIBUTE TO THE LIKELIHOOD OF  
ANOMALOUS WARMTH. DECADAL CLIMATE TRENDS ALSO SUPPORT THE OUTLOOK AND ARE A  
COMPONENT OF THE DYNAMICAL MODEL GUIDANCE. THESE FORECAST TOOLS ALSO SUPPORT  
ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES FOR ALASKA.  
 
POSITIVE SOIL MOISTURE ANOMALIES, COMBINED WITH PROBABILITIES FAVORING  
ABOVE-MEDIAN PRECIPITATION, SUPPORT SOME EXPANION OF THE RELATIVE TEMPERATURE  
WEAKNESS OVER PARTS OF THE ROCKIES AND PLAINS STATES FOR JJA AND JAS.  
ADDITIONALLY, ANTECEDENT TROPICAL AND EXTRATROPICAL SST BOUNDARY CONDITIONS MAY  
INDICATE SOME COMPONENT OF INTERANNUAL VARIABILITY THAT COULD DESTRUCTIVELY  
INTERFERE WITH LONGER TERM WARMING TRENDS OVER PARTS OF THE CENTRAL AND EASTERN  
CONUS. WHILE THE FORECAST STILL BROADLY FAVORS ABOVE-NORMAL TEMPERATURES, THE  
PROBABILITIES ARE NOT EXCEPTIONAL, AND INDEED THE NMME FORECAST AND THE  
OFFICIAL FORECAST SUGGEST A SLIGHTLY COOLER FORECAST FOR THE CONUS AS A WHOLE  
THAN THAT ISSUED FOR LAST SUMMER FOR JJA AND JAS.  
 
SUBTLE CHANGES WERE MADE TO LATER LEADS, FROM ASO TO FMA, BASED ON THE LATEST  
MODEL GUIDANCE AND STATISTICAL FORECASTS THAT EMPHASIZE A SLIGHT TILT TOWARD EL  
NINO IMPACTS. GENERALLY THIS IS SEEN AS A SLIGHT INCREASE IN PROBABILITIES  
FAVORING ABOVE-NORMAL TEMPERATURE ACROSS THE NORTHERN TIER OF THE CONUS, AND A  
REDUCTION OF THE SAME ACROSS THE FAR SOUTHERN TIER.  
 
HIGH PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE INDICATED FOR THE NORTH  
SLOPE OF ALASKA DURING SON AND OND 2017 DUE TO DECADAL TRENDS IN THE SEASONAL  
CYCLE OF SEA ICE.  
 
PRECIPITATION  
 
FOR PRECIPITATION, THE JJA AND JAS 2017 OUTLOOKS INDICATE ABOVE-MEDIAN  
PRECIPITATION FOR AREAS OF THE ROCKY MOUNTAINS AND TO THE EAST, INCLUDING PARTS  
OF THE CENTRAL AND NORTHERN PLAINS. IN THE CASE OF JJA, A SLIGHT ENHANCEMENT OF  
PROBABILITIES FAVORING ABOVE-MEDIAN TEMPERATURES EXTENDS SOUTHWARD THROUGH  
TEXAS. FROM ASO THROUGH OND 2017, INCREASING CHANCES FOR EL NINO CONDITIONS AND  
DYNAMICAL MODEL FORECASTS OF GREATER THAN AVERAGE SSTS IN THE EASTERN TROPICAL  
PACIFIC LEAD TO A SOUTHWARD SHIFT OF THIS REGION OF LIKELY ABOVE-MEDIAN  
PRECIPITATION INTO THE SOUTHWEST CONUS, EXTENDING ACROSS THE FAR SOUTHERN TIER  
OF THE CONUS WITH STILL MODEST PROBABILITIES.  
 
FOR LATE AUTUMN AND WINTER, FROM NDJ 2017-2018 THROUGH JFM 2018, THE LOW  
PROBABILITY OF A LA NINA AND ELEVATED CHANCES FOR A POSSIBLE EL NINO NOW RESULT  
IN THE INTRODUCTION OF PROBABILITIES ASSOCIATED WITH A CANONICAL EL NINO,  
ALBEIT AT VERY LOW AMPLITUDE AND COVERAGE DUE TO THE HIGH UNCERTAINTY.  
FOLLOWING JFM 2018, WEAK SIGNALS DUE TO DECADAL TRENDS IN PRECIPITATION ARE  
INDICATED, INCLUDING BELOW-MEDIAN PRECIPITATION FOR PARTS OF THE SOUTHWEST  
BEGINNING WITH THE MAM 2018 SEASON AND ABOVE-MEDIAN PRECIPITATION IN THE  
NORTHERN-CENTRAL CONTIGUOUS U.S. BEGINNING WITH MAM 2018.  
 
OVER ALASKA, CALIBRATED DYNAMICAL GUIDANCE FAVORS A SHIFT TOWARD ABOVE-MEDIAN  
PRECIPITATION FOR PARTS OF THE MAINLAND DURING THE EARLY LEADS. DURING SON,  
MODEST PROBABILITIES FAVORING ABOVE-MEDIAN PRECIPITATION ARE INTRODUCED OVER  
SOUTHERN ALASKA TO ACCOUNT FOR THE TILT TOWARD EL NINO; THAT SIGNAL CONTINUES  
IN THE FORECASTS THROUGH JFM 2018.  
 
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 JUN 15 2017  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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