439  
FXUS05 KWBC 211330  
PMD90D  
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EST THU DEC 21 2017  
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  
 
LA NINA CONDITIONS CONTINUE ACROSS THE EQUATORIAL PACIFIC OCEAN, AS REPRESENTED  
IN CURRENT OCEANIC AND ATMOSPHERIC OBSERVATIONS. THE OFFICIAL CPC ENSO FORECAST  
INDICATES THAT LA NINA IS LIKELY TO PERSIST THROUGH THE NORTHERN HEMISPHERE  
WINTER 2017-18. A TRANSITION TO ENSO-NEUTRAL CONDITIONS DURING THE MID-TO-LATE  
SPRING IS FORECAST. ENSO-NEUTRAL CONDITIONS ARE FAVORED TO PERSIST THROUGH AT  
LEAST THE BOREAL SUMMER.  
 
THE JANUARY-FEBRUARY-MARCH (JFM) 2018 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL  
TEMPERATURES ACROSS THE SOUTHERN TIER OF THE CONUS, WITH THE HIGHEST ODDS  
(GREATER THAN 50 PERCENT) FORECAST ACROSS THE SOUTHWEST. A SLIGHT TILT IN THE  
ODDS TOWARD ABOVE-NORMAL TEMPERATURES IS FORECAST ALONG THE EAST COAST.  
ABOVE-NORMAL TEMPERATURES ARE ALSO FAVORED FOR NORTHERN MAINLAND ALASKA AND THE  
ALEUTIANS. INCREASED CHANCES FOR BELOW-NORMAL TEMPERATURES DURING JFM ARE  
FORECAST FROM PARTS OF THE PACIFIC NORTHWEST EAST TO THE NORTHERN GREAT PLAINS,  
UPPER MISSISSIPPI VALLEY, AND GREAT LAKES. BELOW-NORMAL TEMPERATURES ARE ALSO  
FAVORED FOR SOUTHEAST MAINLAND ALASKA AND THE ALASKA PANHANDLE.  
 
THE JFM 2018 PRECIPITATION OUTLOOK INDICATES ENHANCED PROBABILITIES OF  
ABOVE-NORMAL PRECIPITATION AMOUNTS FOR PARTS OF THE PACIFIC NORTHWEST ALONG  
WITH NORTHERN AREAS OF THE GREAT BASIN, ROCKIES, AND GREAT PLAINS. INCREASED  
CHANCES OF ABOVE-NORMAL PRECIPITATION ARE ALSO FAVORED FROM THE GREAT LAKES  
SOUTH TO THE OHIO AND TENNESSEE VALLEYS ALONG WITH NORTHERN AND WESTERN  
MAINLAND ALASKA. BELOW-NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE  
SOUTHEAST, GULF COAST, CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, AND MUCH  
OF CALIFORNIA. THE MOST LIKELY AREA TO RECEIVE BELOW-NORMAL PRECIPITATION  
AMOUNTS IS SOUTHERN GEORGIA AND FLORIDA.  
 
EQUAL CHANCES (EC) ARE FORECAST AMONG AREAS WHERE 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 OBSERVATIONS INDICATE THAT LA NINA CONDITIONS STRENGTHENED DURING THE  
PAST TWO MONTHS AS EQUATORIAL SSTS ANOMALIES BECAME INCREASINGLY NEGATIVE FROM  
THE DATE LINE TO THE SOUTH AMERICAN COAST. ABOVE-NORMAL SSTS ARE CURRENTLY  
OBSERVED OVER THE WEST PACIFIC. ALTHOUGH SUB-SURFACE TEMPERATURE ANOMALIES  
WEAKENED SLIGHTLY SINCE OCTOBER, THE EQUATORIAL UPPER-OCEAN ANOMALIES REMAINED  
LARGELY NEGATIVE FROM 180-100W. THE MOST RECENT ONI VALUE (SEPTEMBER NOVEMBER  
2017), BASED ON SST DEPARTURES FROM AVERAGE IN THE NINO 3.4 REGION, IS -0.7  
DEGREES C.  
 
THE RECENT ATMOSPHERIC OBSERVATIONS REMAIN CONSISTENT WITH LA NINA WITH  
ENHANCED (SUPPRESSED) CONVECTION CENTERED OVER THE MARITIME CONTINENT (DATE  
LINE). SINCE OCTOBER 2017, THE MADDEN-JULIAN OSCILLATION (MJO) WAS QUITE ACTIVE  
BUT THE LOW-FREQUENCY STATE REMAINS THE MAJOR INFLUENCE ON ANOMALOUS TROPICAL  
CONVECTION. ANOMALOUS EASTERLY WINDS AT 850-HPA WERE OBSERVED ACROSS THE  
CENTRAL EQUATORIAL PACIFIC DURING THE PAST MONTH. THE ENHANCED PHASE OF THE MJO  
IS FORECAST TO PROPAGATE EAST ACROSS THE WESTERN HEMISPHERE DURING THE NEXT TWO  
WEEKS AND MAY REEMERGE OVER THE INDIAN OCEAN DURING EARLY JANUARY 2018. THIS  
EVOLUTION OF THE MJO MAY PLAY A ROLE IN THE CIRCULATION PATTERN AND  
TEMPERATURES ACROSS THE MID-LATITUDES OF NORTH AMERICA LATER IN JANUARY 2018.  
 
PROGNOSTIC DISCUSSION OF SST FORECASTS  
 
THE CPC SST CONSOLIDATION FORECAST, WHICH INCLUDES THREE STATISTICAL FORECASTS  
ALONG WITH THE CFS, PREDICTS A TRANSITION FROM LA NINA TO ENSO-NEUTRAL  
CONDITIONS DURING SPRING 2018 WITH ENSO-NEUTRAL CONDITIONS FAVORED THEREAFTER.  
THE NORTH AMERICAN MULTI MODEL ENSEMBLE (NMME) ENSEMBLE MEAN FORECAST FOR THE  
NINO-3.4 SST ANOMALY IS SIMILAR TO THE PREVIOUS MONTH, WITH A GRADUAL  
TRANSITION TO ENSO-NEUTRAL CONDITIONS AFTER THE NORTHERN HEMISPHERE WINTER.  
BASED ON THE LATEST OBSERVATIONS AND MODEL FORECASTS, THE OFFICIAL CPC/IRI ENSO  
OUTLOOK FAVORS ENSO-NEUTRAL CONDITIONS BY AMJ 2018.  
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS  
 
THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR JFM 2018 WERE BASED ON DYNAMICAL  
MODEL GUIDANCE AND STATISTICAL TOOLS THAT INCLUDE A CONSTRUCTED ANALOG BASED ON  
GLOBAL SST ANOMALY PATTERNS AND CANONICAL CORRELATION ANALYSIS THAT USES THE  
EVOLUTION OF SST AND SEA-LEVEL PRESSURE AS PREDICTORS. CLIMATE EFFECTS  
TYPICALLY ASSOCIATED WITH LA NINA DURING THE WINTER WERE ALSO USED IN CREATING  
THE OUTLOOKS FOR JFM 2018. DURING THE NEXT FOUR LEADS (FMA THROUGH MJJ 2018),  
THE PRIMARY FACTORS IN CREATING THE SUBSEQUENT OUTLOOKS WERE THE CALIBRATED  
PROBABILISTIC FORECASTS FROM THE NMME. THE LATER OUTLOOKS THROUGH NEXT WINTER  
2018-19 WERE BASED ON TRENDS AND THE CPC CONSOLIDATION FORECAST.  
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - JFM 2018 TO JFM 2019  
 
TEMPERATURE  
 
ABOVE-NORMAL TEMPERATURES DURING JFM 2018 ARE MOST LIKELY (ABOVE 50 PERCENT) TO  
BE OBSERVED ACROSS THE SOUTHWESTERN CONUS, WHICH IS CONSISTENT WITH LA NINA  
TEMPERATURE COMPOSITES, VARIOUS STATISTICAL TOOLS, DYNAMICAL MODEL FORECASTS,  
AND TRENDS. ABOVE-NORMAL TEMPERATURES, ALBEIT WITH LOWER PROBABILITIES, ARE  
ALSO FAVORED FOR THE GULF COAST STATES AND ALONG THE EAST COAST, BASED ON GOOD  
AGREEMENT AMONG THE DYNAMICAL MODELS. LA NINA TEMPERATURE COMPOSITES DURING JFM  
SUPPORT BELOW-NORMAL TEMPERATURES ACROSS THE PACIFIC NORTHWEST, NORTHERN  
ROCKIES, NORTHERN GREAT PLAINS, AND UPPER MISSISSIPPI VALLEY. STATISTICAL  
METHODS CONTINUE TO OFFER A COLDER SOLUTION ACROSS THESE AREAS COMPARED TO THE  
DYNAMICAL MODELS. BELOW-NORMAL TEMPERATURES ARE SLIGHTLY FAVORED FROM THE  
PACIFIC NORTHWEST TO THE GREAT LAKES REGION, GIVEN THE WELL-ESTABLISHED LA NINA  
CONDITIONS AND ASSOCIATED TELECONNECTIONS.  
 
BELOW-NORMAL TEMPERATURES ARE EXPECTED ACROSS THE CENTRAL AND EASTERN U.S.,  
NORTH OF THE 40TH PARALLEL, TO BEGIN JANUARY 2018. THE MADDEN-JULIAN  
OSCILLATION (MJO) MAY PLAY A ROLE IN THE OBSERVED TEMPERATURES ACROSS THE  
MID-LATITUDES OF THE CONUS LATER IN JANUARY. AS OF DECEMBER 19, DYNAMICAL MODEL  
FORECASTS INDICATE THAT THE ENHANCED PHASE OF THE MJO IS LIKELY TO PROPAGATE  
EAST TO THE INDIAN OCEAN AT THE BEGINNING OF JANUARY. IF THE MJO EVOLVES IN  
THIS MANNER, THEN A PATTERN CHANGE FAVORING ABOVE-NORMAL TEMPERATURES MAY OCCUR  
ACROSS THE CENTRAL AND EASTERN U.S. DURING THE LATTER HALF OF JANUARY. THIS MJO  
EVOLUTION DURING THE NEXT FEW WEEKS AND THE POTENTIAL FOR CONTINUED SUBSEASONAL  
VARIABILITY THROUGH THE WINTER ARE A LIMIT FORECAST CONFIDENCE AND  
PROBABILITIES IN THE TEMPERATURE OUTLOOK FOR JFM 2018.  
 
THE TEMPERATURE OUTLOOK FOR FMA 2018 IS SIMILAR TO JFM WITH LITTLE CHANGE AMONG  
THE DYNAMICAL AND STATISTICAL TOOLS. AS A SHIFT TO ENSO-NEUTRAL CONDITIONS IS  
LIKELY TO OCCUR DURING THE SPRING, THE TEMPERATURE OUTLOOKS FROM MAM THROUGH  
MJJ 2018 ARE BASED LARGELY ON THE CALIBRATED PROBABILITY FORECASTS FROM THE  
NMME ALONG WITH TRENDS. PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES WERE  
INCREASED SLIGHTLY ACROSS THE SOUTHERN GREAT PLAINS FROM AMJ THROUGH JJA 2018,  
COMPARED TO THE PREVIOUS OUTLOOK, DUE TO AN INCREASING CHANCE OF DROUGHT AND  
LOW SOIL MOISTURE CONDITIONS AT THOSE TIME LEADS. DURING THE FALL AND WINTER  
2018-19, THE TEMPERATURE OUTLOOKS WERE BASED PRIMARILY ON TRENDS.  
 
PRECIPITATION  
 
THE JFM 2018 PRECIPITATION OUTLOOK IS BASED ON LA NINA COMPOSITES AND INPUT  
FROM THE VARIOUS DYNAMICAL MODELS. PRECIPITATION TOOLS FAVOR A TIGHT GRADIENT  
BETWEEN AREAS FAVORED TO RECEIVE BELOW- AND ABOVE-NORMAL PRECIPITATION ACROSS  
THE SOUTHERN TO NORTHERN TIER OF THE CONUS, RESPECTIVELY. BASED ON GOOD  
AGREEMENT AMONG MOST OF THE DYNAMICAL MODEL FORECASTS INCLUDING THE NMME AND  
IMME, A SLIGHT TILT IN THE ODDS FOR BELOW-NORMAL PRECIPITATION WAS EXPANDED TO  
INCLUDE NEARLY ALL OF CALIFORNIA THROUGH THEIR WET SEASON. THIS FAVORED AREA  
FOR BELOW-NORMAL PRECIPITATION IS ALSO CONSISTENT WITH PRECIPITATION COMPOSITES  
FROM BACK-TO-BACK LA NINA WINTERS. THE HIGHEST PROBABILITIES (EXCEEDING 50  
PERCENT FOR BELOW) IN THE PRECIPITATION OUTLOOK FOR JFM ARE FORECAST ACROSS  
SOUTHERN GEORGIA AND FLORIDA. BASED ON THE LATEST NMME CALIBRATED PROBABILITY  
FORECAST, BELOW-NORMAL PRECIPITATION IS FAVORED ACROSS THE SOUTHERN HIGH PLAINS  
THROUGH MJJ 2018.  
 
COVERAGE OF FAVORED AREAS FOR ANOMALOUS PRECIPITATION DECREASE DURING THE  
SUMMER AS FORECAST CONFIDENCE DIMINISHES WITH A WEAKENING SIGNAL AMONG TOOLS  
AND CONVECTIVE PRECIPITATION BECOME MORE DOMINANT. DURING JJA AND JAS 2017,  
BELOW (ABOVE)-MEDIAN PRECIPITATION FAVORED FOR THE PACIFIC NORTHWEST  
(NORTHEAST) IS RELATED TO HISTORICAL TRENDS.  
 
FORECASTER: BRAD PUGH  
 
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 JAN 18 2018  
 
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011  
FORECAST RELEASE.  

 
 
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