024  
FXUS05 KWBC 151231  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU APR 15 2021  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
LA NINA CONDITIONS CONTINUE ACROSS THE EQUATORIAL PACIFIC OCEAN AS INDICATED BY  
OCEANIC AND ATMOSPHERIC CONDITIONS, WHILE INDICATIONS OF A POTENTIAL TRANSITION  
TO ENSO-NEUTRAL DURING THE MAY THROUGH JULY PERIOD ARE APPARENT. THE CHANCE OF  
A RETURN TO LA NINA INCREASES OVER THE SUMMER, SUCH THAT LA NINA BECOMES  
SLIGHTLY MORE FAVORED THAN ENSO-NEUTRAL IN AUTUMN. IN ADDITION TO THE FORECAST  
ENSO EVOLUTION DESCRIBED ABOVE, CURRENT ANOMALOUS SOIL MOISTURE ALONG WITH  
NUMERICAL AND STATISTICAL MODEL GUIDANCE INFORM THE SEASONAL TEMPERATURE AND  
PRECIPITATION OUTLOOKS.  
 
 
 
THE MAY-JUNE-JULY (MJJ) 2021 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL SEASONAL  
MEAN TEMPERATURES FOR NEARLY ALL THE CONTIGUOUS U.S. AND FOR MAINLAND ALASKA  
AND THE ALEUTIAN ISLANDS. EQUAL CHANCES (EC) OF ABOVE-NORMAL AND BELOW-NORMAL  
TEMPERATURES ARE PREDICTED FOR A REGION FROM FAR SOUTHEASTERN MAINLAND ALASKA  
TO PARTS OF THE PACIFIC NORTHWEST, INCLUDING NORTHWESTERN OREGON AND WESTERN  
WASHINGTON. ABOVE-NORMAL TEMPERATURES ARE MOST LIKELY FOR THE ENTIRE FORECAST  
DOMAIN FROM THE SUMMER INTO THE BEGINNING OF AUTUMN.  
 
 
 
THE MJJ 2021 PRECIPITATION OUTLOOK FAVORS ABOVE-NORMAL SEASONAL TOTAL  
PRECIPITATION AMOUNTS FOR CENTRAL AND EASTERN AREAS SURROUNDING THE GREAT  
LAKES, THE MIDWEST, THE MID-ATLANTIC, AND MOST OF THE NORTHEAST, EXCEPT FOR  
NORTHERN MAINE, AS WELL AS SOUTHWARD ALONG THE EASTERN SEABOARD AND THE EASTERN  
GULF COAST. ABOVE-NORMAL PRECIPITATION IS ALSO FAVORED FOR NORTHWESTERN AREAS  
OF ALASKA, INCLUDING THE NORTH-CENTRAL COAST. BELOW-NORMAL PRECIPITATION IS  
MOST LIKELY FOR A REGION FROM THE WEST COAST ACROSS THE ROCKIES TO THE CENTRAL  
AND SOUTHERN GREAT PLAINS, EXCLUDING AREAS OF THE SOUTHWEST THAT ARE  
CLIMATOLOGICALLY DRIER AT THIS TIME OF YEAR. THE AREA OF LIKELY BELOW-NORMAL  
PRECIPITATION IS FORECAST TO SLOWLY SHIFT NORTHWARD AND EASTWARD DURING THE  
SUMMER SEASONS WHILE ABOVE-NORMAL PRECIPITATION CONTINUES TO BE FAVORED ALONG  
THE EASTERN SEABOARD AND EXPANDS WESTWARD ALONG THE GULF COAST OVER THE SAME  
PERIOD. AN AREA OF ELEVATED PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION IS  
INTRODUCED FOR PARTS OF THE SOUTHWEST DURING THE MONSOON SEASON.  
 
 
 
EQUAL CHANCES (EC) ARE INDICATED FOR AREAS WHERE SEASONAL MEAN TEMPERATURES AND  
SEASONAL TOTAL 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  
 
LA NINA CONDITIONS CONTINUED BUT WEAKENED DURING THE LAST MONTH IN THE  
EQUATORIAL PACIFIC OCEAN AS SHOWN BY BOTH OCEANIC AND ATMOSPHERIC INDICATORS.  
EQUATORIAL SEA SURFACE TEMPERATURE (SST) ANOMALIES BECAME LESS NEGATIVE OVER  
THE CENTRAL EQUATORIAL PACIFIC DURING THE LAST MONTH. THE MOST RECENT WEEKLY  
VALUE OF THE NINO3.4 SST INDEX IS -0.5 DEGREES C. SSTS AND ATMOSPHERIC  
CONDITIONS ARE LIKELY TO BE MODULATED BY AN ONGOING MJO EVENT OVER THE NEXT FEW  
WEEKS. BELOW THE SURFACE, THE DEPTH AND MAGNITUDE OF NEGATIVE OCEAN TEMPERATURE  
ANOMALIES DECREASED AND CURRENTLY EXTEND IN A SHALLOW LAYER TO A DEPTH OF 50  
METERS FROM 175 E TO 110 W. POSITIVE SUBSURFACE OCEANIC HEAT CONTENT ANOMALIES  
ARE PRESENT BELOW 50 METERS TO DEPTHS OF 200 METERS OR MORE AND HAVE EXPANDED  
EASTWARD IN THE WESTERN AND EAST-CENTRAL PACIFIC OCEAN.  
 
 
 
SUPPRESSED CONVECTION PERSISTS ACROSS THE EQUATORIAL PACIFIC SURROUNDING THE  
 
DATE LINE, WHILE ENHANCED CONVECTION WEAKENED OVER THE WESTERN PACIFIC BUT  
REMAINS OVER PARTS OF INDONESIA AND THE PHILIPPINES. RECENT MONTHLY AVERAGE  
850-HPA WINDS CONTINUE TO SHOW ENHANCED EASTERLY TRADE WINDS ACROSS THE WESTERN  
AND EAST-CENTRAL EQUATORIAL PACIFIC. WESTERLY WIND ANOMALIES CONTINUED AT  
200-HPA OVER MUCH OF THE EQUATORIAL PACIFIC OCEAN. THESE OCEAN AND ATMOSPHERE  
INDICATORS SHOW THE COUPLED OCEAN-ATMOSPHERE SYSTEM IS CONSISTENT WITH  
WEAKENING LA NINA CONDITIONS.  
 
PROGNOSTIC DISCUSSION OF SST FORECASTS  
 
FORECASTS OF THE NINO3.4 SST INDEX FROM THE NMME SHOW CONSIDERABLE SPREAD IN  
 
ENSEMBLE MEMBERS BOTH ACROSS THE MODELING CENTER FORECASTS AND WITHIN EACH  
MODELING CENTER ENSEMBLE BY THE START OF SUMMER. MOST GUIDANCE FAVORS A  
CONTINUED DECREASE IN THE MAGNITUDE OF NEGATIVE SST ANOMALIES OVER THE NEXT  
THREE MONTHS, AND THE OFFICIAL CONSENSUS CALLS FOR ENSO-NEUTRAL WITH A  
PROBABILITY OF 80 PERCENT. FORECASTS BEGIN TO DIVERGE DURING THE SUMMER MONTHS  
WITH SOME GUIDANCE FAVORING A DECREASE IN NINO3.4 SEA SURFACE TEMPERATURES,  
SUGGESTING A RETURN TO LA NINA CONDITIONS BY AUTUMN 2021. THE CA AND MARKOV  
STATISTICAL MODELS IN THE CPC NINO3.4 SST CONSOLIDATED FORECAST INDICATE A  
TRAJECTORY TOWARDS ENSO-NEUTRAL IN THE AUTUMN, WHILE THE CCA PREDICTS A STEADY  
RISE IN NINO3.4 SST TOWARDS EL NINO CONDITIONS OVER THE SUMMER AND AUTUMN  
MONTHS.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
ALTHOUGH EQUATORIAL PACIFIC SSTS CONTINUE TO RISE TOWARDS CLIMATOLOGICAL NORMAL  
VALUES AND ARE FORECAST TO INDICATE ENSO-NEUTRAL OCEANIC CONDITIONS FOR MJJ  
2021, TYPICAL IMPACTS OF LA NINA ARE CONSIDERED IN PREPARING THE MJJ 2021  
SEASONAL OUTLOOK, AS SOME IMPACTS ARE LIKELY TO RESULT AT THE START OF THE  
SEASON. TOOLS USED TO INFORM THE OUTLOOKS INCLUDE REGRESSIONS OF TEMPERATURE  
AND PRECIPITATION ON THE NINO3.4 SST CONSOLIDATION FORECAST AND THE CBAM  
FORECAST TOOL, THAT STATISTICALLY BRIDGES DYNAMICAL MODEL NINO3.4 SST ANOMALY  
FORECASTS FROM THE NMME WITH OBSERVED TEMPERATURE AND PRECIPITATION USING A  
BAYESIAN METHODOLOGY.  
 
 
 
CURRENT ANOMALOUS SOIL MOISTURE AND SNOW COVER ARE CONSIDERED AND CONTRIBUTED  
 
TO THE OUTLOOK IN SOME LOCATIONS FOR THE MJJ 2021 SEASON. DYNAMICAL MODEL  
FORECASTS FROM THE NMME AND COPERNICUS (C3S) MULTI-MODEL ENSEMBLE SYSTEMS ARE  
USED EXTENSIVELY FOR THE FIRST SIX LEADS WHEN THEY ARE AVAILABLE, AS WAS THE  
OBJECTIVE, HISTORICAL SKILL WEIGHTED CONSOLIDATION, THAT COMBINES BOTH  
DYNAMICAL AND STATISTICAL FORECAST TOOLS. DUE TO THE FREQUENCY OF BACK-TO-BACK  
LA NINA EVENTS IN THE HISTORICAL RECORD AND THE CONSENSUS ENSO OUTLOOK SLIGHTLY  
FAVORING LA NINA OVER ENSO NEUTRAL, POTENTIAL IMPACTS OF REDEVELOPMENT OF LA  
NINA IS CONSIDERED IN THE AUTUMN AND WINTER SEASONS. DECADAL TIMESCALE TRENDS  
IN TEMPERATURE AND PRECIPITATION ARE UTILIZED EXTENSIVELY TO INFORM THE  
SEASONAL OUTLOOKS AT ALL LEADS.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2021 TO MJJ 2022  
 
TEMPERATURE  
 
THE MJJ 2021 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL SEASONAL MEAN TEMPERATURES  
FOR NEARLY ALL THE CONTIGUOUS U.S. (CONUS) AND FOR THE ALASKA MAINLAND AND THE  
ALEUTIAN ISLANDS. THE GREATEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE  
LOCATED OVER THE SOUTHWEST IN THE FOUR CORNERS REGION, EXCEEDING 70 PERCENT,  
DUE TO MULTIPLE FACTORS INCLUDING VERY CONSISTENT DYNAMICAL MODEL GUIDANCE, LOW  
SOIL MOISTURE CONDITIONS, POSITIVE DECADAL TEMPERATURE TRENDS, AND THE SUPPORT  
OF STATISTICAL FORECAST TOOLS. MODESTLY ELEVATED PROBABILITIES FOR ABOVE-NORMAL  
TEMPERATURES EXTEND EASTWARD ACROSS THE SOUTHEAST AND NORTHWARD ALONG THE  
EASTERN SEABOARD TO NEW ENGLAND, SUPPORTED BY MODEL GUIDANCE AND POSITIVE  
DECADAL TRENDS. GREATER UNCERTAINTY, RELATED TO THE EARLY IMPACTS OF LA NINA  
AND AN MJO EVENT, LOWER HISTORICAL FORECAST SKILL IN MODEL GUIDANCE, AND WEAKER  
DECADAL TEMPERATURE TRENDS DECREASE PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES  
IN THE NORTH-CENTRAL CONUS. CONSISTENT WITH POSSIBLE LINGERING LA NINA IMPACTS  
AS INDICATED BY ENSO REGRESSIONS AND HYBRID STATISTICAL-DYNAMICAL "BRIDGING"  
TOOLS, EQUAL CHANCES OF ABOVE-NORMAL AND BELOW-NORMAL TEMPERATURES ARE FORECAST  
FOR SOUTHEASTERN AREAS OF ALASKA AND PARTS OF THE PACIFIC NORTHWEST, AND THE  
PROBABILITIES OF ABOVE-NORMAL TEMPERATURES HAVE BEEN DECREASED FOR THE SOUTHERN  
ALASKA MAINLAND. NEGATIVE TRENDS IN SEA ICE COVERAGE AND THICKNESS AND POSITIVE  
DECADAL TEMPERATURE TRENDS FAVOR ABOVE-NORMAL TEMPERATURES FOR NORTHERN AREAS  
OF ALASKA.  
 
 
 
DYNAMICAL MODEL GUIDANCE AND STATISTICAL FORECAST TOOLS, INCLUDING THOSE  
DERIVED FROM FORECASTS OF THE ENHANCED PROBABILITIES OF ENSO-NEUTRAL OR LA NINA  
CONDITIONS AND DECADAL TIMESCALE TRENDS, FAVOR CONTINUED ELEVATED PROBABILITIES  
FOR ABOVE-NORMAL TEMPERATURES FOR MOST OF THE FORECAST DOMAIN THROUGH THE SON  
2021 SEASON WITH THE GREATEST CHANCES INDICATED FOR THE WESTERN U.S. AND ALONG  
THE EASTERN SEABOARD WITH SLIGHTLY LOWER PROBABILITIES FOR THE NORTH-CENTRAL  
CONUS.  
 
 
 
BEGINNING IN OND 2021 AND CONTINUING THROUGH FMA 2022, THERE IS A GRADUAL  
INCREASE IN THE AREA DESIGNATED AS EC, WITH AN INCREASED CHANCE FOR LA NINA  
REDEVELOPMENT WITH POTENTIAL IMPACTS OVER MUCH OF THE NORTHERN TIER OF THE  
CONUS FROM THE PACIFIC NORTHWEST TO THE WESTERN GREAT LAKES, AND LATER  
SOUTHEAST ALASKA. OTHER AREAS OF THE FORECAST DOMAIN CONTINUE TO FAVOR LIKELY  
ABOVE NORMAL TEMPERATURES, PRIMARILY DUE TO POSITIVE DECADAL TEMPERATURE TRENDS.  
 
PRECIPITATION  
 
THE MJJ 2021 PRECIPITATION OUTLOOK FAVORS ABOVE-NORMAL SEASONAL TOTAL  
PRECIPITATION AMOUNTS FOR CENTRAL AND EASTERN AREAS OF THE GREAT LAKES REGION,  
THE OHIO VALLEY, THE MID-ATLANTIC, AND MOST OF THE EASTERN SEABOARD, EXCLUDING  
NORTHERN MAINE, BASED ON THE CONTINUED INFLUENCE OF LA NINA EARLY IN THE  
SEASON, POSITIVE PRECIPITATION DECADAL TRENDS, OTHER STATISTICAL FORECAST TOOLS  
INCLUDING THE CONSTRUCTED ANALOG FROM SOIL MOISTURE CONDITIONS, AND SOME  
DYNAMICAL MODEL FORECASTS FROM THE NMME AND C3S ENSEMBLE SYSTEMS. THERE IS  
CONSIDERABLY GREATER AGREEMENT AMONG DYNAMICAL MODELS, HOWEVER, FOR A REGION OF  
LIKELY BELOW-NORMAL PRECIPITATION FROM THE CENTRAL AND NORTHERN PACIFIC COAST  
ACROSS THE ROCKIES INTO THE CENTRAL AND SOUTHERN PLAINS. HIGHER PROBABILITIES  
FOR BELOW-NORMAL OVER THE NORTHERN ROCKIES, EXCEEDING 50 PERCENT IN SOME AREAS,  
ARE SUPPORTED BY TYPICAL LA NINA IMPACTS AND DYNAMICAL MODEL FORECASTS.  
 
 
 
THE AREA OF LIKELY BELOW-NORMAL PRECIPITATION IS FORECAST TO SHIFT SLOWLY  
NORTHWARD AND EASTWARD DURING THE SUMMER AND SOUTHWARD INTO THE WEST-CENTRAL  
CONUS DURING THE AUTUMN, CONSISTENT WITH DYNAMICAL MODEL GUIDANCE. ABOVE-NORMAL  
PRECIPITATION IS PREDICTED TO PERSIST ALONG MUCH OF THE EASTERN SEABOARD  
THROUGH THE SUMMER MONTHS, AND AN AREA OF LIKELY ABOVE-NORMAL PRECIPITATION  
CONTINUES FOR PARTS OF THE SOUTHEAST ATLANTIC COAST AND THE EASTERN GULF COAST  
INTO THE EARLY AUTUMN, CONSISTENT WITH THE IMPACTS OF THE LIKELY LA NINA OR  
ENSO-NEUTRAL CLIMATE CONDITIONS, WITH VERY LOW PROBABILITY OF EL NINO  
CONDITIONS OVER THE TROPICS.  
 
 
 
BELOW-NORMAL SOIL MOISTURE IN THE SOUTHWEST AND SOUTHERN ROCKIES MAY ALLOW FOR  
MORE EFFICIENT HEATING OF THE LAND MASS AND POTENTIALLY AN ENHANCED MONSOON  
CIRCULATION. ELEVATED PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION ARE  
PREDICTED FOR PARTS OF THE SOUTHWEST FROM JJA THROUGH ASO 2021, SUPPORTED IN  
PART BY DYNAMICAL MODEL FORECASTS.  
 
 
 
DYNAMICAL MODEL GUIDANCE SUPPORTS ABOVE-NORMAL PRECIPITATION FOR PARTS OF THE  
NORTHWESTERN COAST OF ALASKA FROM MJJ THROUGH ASO 2021, WHILE DECADAL  
PRECIPITATION TRENDS RELATED TO POSITIVE TRENDS IN SSTS SUPPORT ABOVE-NORMAL  
PRECIPITATION FOR THE NORTHERN COAST THROUGH OND 2021. THE OUTLOOKS FROM OND  
2021 THROUGH MJJ 2022 ARE PRIMARILY BASED ON DECADAL PRECIPITATION 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 MAY 20 2021  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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