453  
FXUS05 KWBC 211333  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EST THU JAN 21 2021  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
LA NINA CONDITIONS ARE PRESENT ACROSS THE EQUATORIAL PACIFIC OCEAN, AS  
INDICATED BY CURRENT OCEANIC AND ATMOSPHERIC OBSERVATIONS. LA NINA IS EXPECTED  
TO CONTINUE THROUGH THE NORTHERN HEMISPHERE WINTER (~95% CHANCE), WITH A  
POTENTIAL TRANSITION TO ENSO-NEUTRAL (~55% CHANCE) DURING APRIL-MAY-JUNE 2021.  
THE FEBRUARY-MARCH-APRIL (FMA) TEMPERATURE OUTLOOK FAVORS BELOW NORMAL SEASONAL  
MEAN TEMPERATURES FOR THE SOUTHERN HALF OF MAINLAND ALASKA, THE ALASKA  
PANHANDLE, AND FROM THE PACIFIC NORTHWEST EASTWARD TO THE NORTHERN ROCKIES.  
ABOVE NORMAL SEASONAL MEAN TEMPERATURES ARE FAVORED ACROSS PARTS OF NORTHERN  
AND WESTERN ALASKA, AND FOR MOST OF THE CONUS, EXCEPT PORTIONS OF THE NORTHERN  
PLAINS, NORTHERN ROCKIES, SOUTHERN OREGON, AND NORTHERN CALIFORNIA. MAXIMUM  
PROBABILITIES FOR ABOVE NORMAL TEMPERATURES EXCEED 60% ACROSS PARTS OF THE  
SOUTHWEST AND SOUTHERN GREAT PLAINS. THE FMA PRECIPITATION OUTLOOK FAVORS ABOVE  
NORMAL PRECIPITATION FOR MOST OF THE NORTHERN TIER OF THE CONUS, EXTENDING FROM  
THE PACIFIC NORTHWEST TO THE GREAT LAKES, THEN SOUTHWARD ACROSS EASTERN  
PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE OHIO VALLEY, AND THE CENTRAL AND  
NORTHERN APPALACHIANS. ABOVE NORMAL PRECIPITATION IS ALSO FAVORED FOR NORTHERN  
AND WESTERN PORTIONS OF ALASKA. MAXIMUM PROBABILITIES FOR ABOVE NORMAL  
PRECIPITATION EXCEED 50% OVER THE OHIO VALLEY. FROM CENTRAL AND SOUTHERN  
CALIFORNIA ACROSS THE GREAT BASIN TO THE CENTRAL AND SOUTHERN PLAINS, BELOW  
NORMAL PRECIPITATION IS FAVORED. BELOW NORMAL PRECIPITATION IS THE MOST FAVORED  
OUTCOME ACROSS PORTIONS OF THE SOUTHEAST, AS WELL AS ALONG THE SOUTHERN COAST  
OF MAINLAND ALASKA AND FOR THE ALASKA PANHANDLE.  
 
EQUAL CHANCES (EC) ARE FORECAST FOR AREAS WHERE PROBABILITIES FOR EACH CATEGORY  
OF SEASONAL MEAN TEMPERATURES OR SEASONAL TOTAL PRECIPITATION AMOUNTS ARE  
PREDICTED 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  
 
TROPICAL OCEANIC AND ATMOSPHERIC OBSERVATIONS REFLECT ONGOING LA NINA  
CONDITIONS. DURING THE PAST 30-DAYS, AN AREA OF NEGATIVE SEA-SURFACE  
TEMPERATURE (SST) ANOMALIES WAS LOCATED FROM ABOUT 160 DEG E TO THE COAST OF  
SOUTH AMERICA. SST ANOMALIES FOR THE PERIOD RANGED BETWEEN 0.5 DEG C TO 1.5 DEG  
C OVER MOST OF THIS REGION, WITH THE STRONGEST ANOMALIES FROM 170-150 DEG W.  
SOME WARMING HAS OCCURRED RECENTLY, EAST OF 135W. SUBSURFACE TEMPERATURES WERE  
COLDER-THAN-AVERAGE FOR THE SAME REGION, DOWN TO A DEPTH OF ABOUT 175 METERS.  
THE OCEANIC NINO 3.4 INDEX (ONI) FOR THE LATEST OBSERVED SEASON (OND 2020) IS  
-1.3 DEG C, WHICH QUALIFIES AS A MODERATE LA NINA AT THIS TIME. ATMOSPHERIC  
OBSERVATIONS REFLECT ENHANCED EASTERLY TRADE WINDS AT 850-HPA FROM THE WESTERN  
TO THE EAST-CENTRAL EQUATORIAL PACIFIC, WESTERLY WIND ANOMALIES AT 200-HPA OVER  
MOST OF THE PACIFIC, AND SUPPRESSED TROPICAL CONVECTION OVER THE WESTERN AND  
CENTRAL PACIFIC. THE ATMOSPHERIC CONDITIONS REFLECT A CANONICAL LA NINA  
RESPONSE.  
 
PROGNOSTIC DISCUSSION OF SST FORECASTS  
 
THE CPC NINO3.4 SST CONSOLIDATION DEPICTS NEGATIVE SST ANOMALIES WEAKENING (SO  
WARMING) THROUGH THE REMAINDER OF THE WINTER AND SPRING OF 2021. THE  
CONSOLIDATION FORECAST PREDICTS THE ONI VALUE WILL CROSS THE -0.5 DEG C  
THRESHOLD INTO ENSO-NEUTRAL TERRITORY DURING FMA 2021, AND REACH THE ZERO  
ANOMALY LINE BY AMJ 2021. THIS IS SLIGHTLY WARMER THAN LAST MONTHS SST CON.  
THE NMME ENSEMBLE MEAN SST PLUME FOR THE NINO 3.4 REGION REACHES THE -0.5 DEG C  
THRESHOLD BY APRIL 2021, AND CONTINUES TO WARM SLIGHTLY THROUGH SUMMER 2021.  
THE C3S (COPERNICUS) SST PLUME REACHES THE ENSO-NEUTRAL THRESHOLD SLIGHTLY  
EARLIER, IN FEB, THEN REMAINS AT OR ABOUT -0.5 DEG C UNTIL JUNE. THE CPC-IRI  
CONSENSUS PREDICTS THE LIKELIHOOD OF LA NINA WILL DROP TO THE SAME LIKELIHOOD  
OF ENSO-NEUTRAL BY ABOUT AMJ 2021. THE OFFICIAL ENSO FORECAST CALLS FOR  
APPROXIMATELY A 95% CHANCE FOR LA NINA TO CONTINUE THROUGH NORTHERN HEMISPHERE  
WINTER, WITH A POTENTIAL TRANSITION DURING THE SPRING 2021 (~55% CHANCE OF ENSO  
NEUTRAL DURING AMJ 2021).  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
GIVEN A VERY HIGH LIKELIHOOD OF THE PERSISTENCE OF LA NINA CONDITIONS, THE  
SEASONAL OUTLOOKS UTILIZED CANONICAL IMPACTS DURING PAST OBSERVED LA NINA  
EVENTS AS GUIDANCE FOR MANY AREAS OF THE FORECAST DOMAIN THROUGH AT LEAST MAM  
2021. THIS GUIDANCE INCLUDED REGRESSIONS OF TEMPERATURE AND PRECIPITATION  
RELATIVE TO THE CPC CONSOLIDATION FORECASTS OF THE NINO3.4 REGION AND VIA  
"BRIDGING" TECHNIQUES UTILIZING STATISTICAL RELATIONSHIPS BETWEEN DYNAMICAL  
MODEL FORECASTS OF THE NINO 3.4 INDEX AND OBSERVED TEMPERATURE AND  
PRECIPITATION. DYNAMICAL MODEL GUIDANCE FROM THE NORTH AMERICAN MULTI-MODEL  
ENSEMBLE (NMME) AND THE MODEL SUITE FROM THE COPERNICUS PROGRAM ARE A  
SIGNIFICANT COMPONENT OF GUIDANCE FOR THE TEMPERATURE AND PRECIPITATION  
OUTLOOKS THROUGH JJA 2021. BEYOND JJA 2021, THE CONSOLIDATION OF VARIOUS  
STATISTICAL TOOLS, INCLUDING DECADAL TRENDS, WAS THE PRIMARY BASIS FOR THE  
OUTLOOKS, WITH LITTLE REMAINING INFLUENCE FROM ENSO OR OTHER RELIABLE  
LARGE-SCALE SIGNALS OF CLIMATE VARIABILITY FOR THESE FORECAST LEADS. PREDICTED  
LOW SOIL MOISTURE CONDITIONS AS A RESULT OF PREDICTED PRECIPITATION TOTALS OVER  
ALREADY DRY AREAS, INFLUENCED THE TEMPERATURE OUTLOOKS FOR THE SPRING AND EARLY  
SUMMER 2021 OVER THE CENTRAL PLAINS AND SOUTHWEST. AT LATER LEADS, DECADAL  
TRENDS IN TEMPERATURE AND PRECIPITATION WERE THE PRIMARY TOOL USED IN CREATING  
THE SEASONAL OUTLOOKS.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - FMA 2021 TO FMA 2022  
 
TEMPERATURE  
 
THE TEMPERATURE OUTLOOK FOR FMA 2021 REFLECTS CURRENT MODEL GUIDANCE, BLENDED  
WITH LIKELY IMPACTS OF LA NINA AND TRENDS. THE FAVORING OF BELOW NORMAL  
TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, THE ALASKA PANHANDLE, AND THE  
PACIFIC NORTHWEST REFLECT LA NINA CONDITIONS. THE OUTLOOK IS SLIGHTLY WARMER  
THAN LAST MONTHS OUTLOOK BUT COLDER THAN THE RECENT MODEL GUIDANCE FOR THIS  
REGION. THE FMA OUTLOOK FOR THE NORTHERN GREAT PLAINS IS WARMER THAN LAST  
MONTHS LEAD 2 OUTLOOK, REFLECTING THE ONGOING LACK OF SNOW COVER AND MORE  
RECENT MODEL GUIDANCE, THOUGH PROBABILITIES ARE MODEST AT BEST FROM NORTH  
DAKOTA TO ILLINOIS. ODDS FOR ABOVE NORMAL TEMPERATURES WERE ALSO INCREASED  
ACROSS THE LOWER MISSISSIPPI, GULF COAST, AND FLORIDA, REFLECTING RECENT MODEL  
GUIDANCE AND LIKELY LA NINA IMPACTS. THE OUTLOOKS FOR LATER SPRING AND SUMMER  
2021 REFLECT RECENT MODEL GUIDANCE AND TRENDS, WITH THE LOWEST PROBABILITIES IN  
THE CENTRAL PORTIONS OF THE CONUS WHERE VARIANCES ARE HIGHEST, MODEL SKILL  
LOWEST, AND TRENDS ARE SMALL TO NEGATIVE. OUTLOOKS FOR NEXT AUTUMN WERE  
UNCHANGED, AS THE REASONING BEHIND THE OUTLOOKS HAS NOT CHANGED FOR THOSE  
PERIODS, AND TRENDS ARE THE MOST RELIABLE TOOL. SOME OUTLOOKS ARE CALLING FOR  
A SECOND LA NINA WINTER, WHICH WOULD NOT BE UNPRECEDENTED SINCE 1950, AND THE  
OUTLOOKS FOR NEXT WINTER ARE ALREADY ALIGNED FOR THAT POSSIBILITY.  
 
PRECIPITATION  
 
LA NINA IS THE PRIMARY PHYSICAL DRIVER BEHIND THE SUBSEQUENT FMA AND MAM  
PRECIPITATION OUTLOOKS, SO ONLY MINOR ADJUSTMENTS WERE NEEDED TO THE  
CORRESPONDING OUTLOOKS MADE LAST MONTH. IN MAM, THE AMPLITUDE OF LA NINA AND  
ITS ASSOCIATED PRECIPITATION IMPACTS ARE EXPECTED TO BEGIN TO DECLINE. IN AMJ  
2021, BELOW NORMAL PRECIPITATION AMOUNTS ARE FORECAST TO DIMINISH IN SPATIAL  
COVERAGE ACROSS THE SOUTHERN CONUS, AND BE CENTERED OVER MOST OF THE  
SOUTHWESTERN QUARTER OF THE CONUS. AFTER AMJ, WITH A PREDICTED ENSO NEUTRAL,  
TRENDS ARE MORE HIGHLY FACTORED, WHICH FAVORS BELOW NORMAL PRECIPITATION FOR  
PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES DURING SUMMER MONTHS, SHIFTING  
SOUTHWARD DURING THE WINTER. EAST OF THE MISSISSIPPI, SUMMER AND EARLY AUTUMN  
MONTHS HAVE A WET TREND. BY NEXT WINTER, DEC-JAN-FEB 2021-22, THE ONLY  
REMAINING SIGNAL IS THE TREND FOR ABOVE NORMAL PRECIPITATION OVER THE NORTHERN  
PLAINS.  
 
FORECASTER: MATTHEW ROSENCRANS  
 
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 FEB 18 2021  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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