PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EST THU NOV 17 2016

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2016

THE DECEMBER 2016 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL 
MODEL GUIDANCE, STATISTICAL TOOLS, AND THE TYPICAL INFLUENCE FROM LA NINA. 
DURING THE PAST COUPLE OF MONTHS, LA NINA CONDITIONS DEVELOPED AS OBSERVED WITH 
NEGATIVE SEA SURFACE TEMPERATURES ACROSS THE EASTERN AND CENTRAL EQUATORIAL 
PACIFIC OCEAN ALONG WITH SUPPRESSED (ENHANCED) CONVECTION ACROSS THE CENTRAL 
TROPICAL PACIFIC (INDONESIA). CLIMATE SIGNALS TYPICALLY ASSOCIATED WITH LA NINA 
WERE CONSIDERED IN MAKING THE DECEMBER 2016 OUTLOOK, GIVEN THESE CURRENT 
ATMOSPHERIC AND OCEANIC STATES. 

ALTHOUGH THE MJO STRENGTHENED DURING EARLY NOVEMBER, ITS EFFECTS ON THE 
EXTRATROPICS ARE UNCLEAR DUE TO INTERFERENCE WITH THE LOW FREQUENCY BASE STATE. 
THE DYNAMICAL MODELS INDICATE A DECREASE IN THE AMPLITUDE OF THE MJO SIGNAL 
DURING THE NEXT WEEK. THEREFORE, THE MJO DID NOT FACTOR INTO THE DECEMBER 
OUTLOOK. ITS EVOLUTION WILL BE CLOSELY MONITORED FOR THE REVISED OUTLOOK AT THE 
END OF NOVEMBER. 

DESPITE EXCELLENT AGREEMENT AMONG THE DYNAMICAL MODELS THAT FAVOR ABOVE-NORMAL 
TEMPERATURES THROUGHOUT THE FORECAST DOMAIN, FORECAST CONFIDENCE IN THE 
TEMPERATURE OUTLOOK IS LOWER THAN WOULD BE EXPECTED. THE ARCTIC OSCILLATION 
(AO) INDEX HAD ONE ITS MOST NEGATIVE VALUES FOR OCTOBER. A NEGATIVE AO INDEX IS 
ASSOCIATED WITH ABOVE (BELOW) NORMAL 500-HPA HEIGHTS AT THE HIGHER (MIDDLE) 
LATITUDES OF THE NORTHERN HEMISPHERE. THIS PATTERN RESULTED IN BELOW-NORMAL 
TEMPERATURES ACROSS PARTS OF EURASIA. HOWEVER, ABOVE-NORMAL TEMPERATURES WERE 
OBSERVED ACROSS MOST OF THE LOWER 48 DURING OCTOBER. AFTER A BRIEF PERIOD WITH 
A POSITIVE AO INDEX, THE GFS MODEL REMAINS CONSISTENT THAT THE AO INDEX BECOMES 
SHARPLY NEGATIVE ONCE AGAIN DURING LATE NOVEMBER. BELOW-NORMAL TEMPERATURES ARE 
TYPICALLY ASSOCIATED WITH A NEGATIVE AO INDEX FROM THE NORTHERN GREAT PLAINS 
SOUTHEAST TO THE SOUTHERN ATLANTIC COASTAL STATES DURING DECEMBER. GIVEN THE 
LARGE DISAGREEMENT BETWEEN TEMPERATURE COMPOSITES OF A NEGATIVE AO INDEX (BELOW 
NORMAL) AND DYNAMICAL MODEL GUIDANCE (ABOVE NORMAL), EQUAL CHANCES FOR BELOW, 
NEAR, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST FROM THE NORTHERN GREAT PLAINS 
EXTENDING INTO THE SOUTHEAST. ELSEWHERE, ABOVE-NORMAL TEMPERATURES ARE FAVORED 
ACROSS NEW ENGLAND AND THE WESTERN CONUS ALTHOUGH PROBABILITIES ARE TEMPERED 
DUE TO THE BLOCKY 500-HPA PATTERN OVER THE NORTHERN HEMISPHERE EXPECTED AT THE 
BEGINNING OF DECEMBER.  

THE PRECIPITATION OUTLOOK FOR DECEMBER IS BASED PRIMARILY ON THE CALIBRATED 
NMME AND IS CONSISTENT WITH LA NINA AND THE DJF PRECIPITATION OUTLOOK. HOWEVER, 
THE FAVORED AREA FOR BELOW-MEDIAN PRECIPITATION OVER THE SOUTHEAST DOES NOT 
EXTEND INTO THE SOUTHWESTERN CONUS SINCE THE LATEST RUNS OF THE CFS INDICATE AN 
UPPER-LEVEL TROUGH OVER THIS REGION DURING EARLY DECEMBER. A SLIGHT TILT IN THE 
ODDS FOR ABOVE-MEDIAN PRECIPITATION DOWNWIND OF THE GREAT LAKES IS BASED ON 
ELEVATED CHANCES OF LAKE-ENHANCED PRECIPITATION WITH THE ABOVE-NORMAL LAKE 
TEMPERATURES. THE PROBABILITIES FOR BELOW (ABOVE)-MEDIAN PRECIPITATION FORECAST 
ACROSS THE SOUTHEASTERN (NORTHWESTERN) CONUS ARE MODEST DUE TO LIMITED SKILL 
INHERENT IN A MONTHLY OUTLOOK AT THIS TIME LEAD. THIS PRECIPITATION OUTLOOK 
WILL LIKELY BE REVISED AT THE END OF NOVEMBER. 

THE HIGHEST ODDS FOR ABOVE-NORMAL TEMPERATURES THROUGHOUT THE FORECAST DOMAIN 
ARE FORECAST ACROSS THE ALEUTIANS WHERE SEA SURFACE TEMPERATURE ANOMALIES ARE 
AVERAGING AS MUCH AS 1.5 DEGREES C ABOVE NORMAL. EQUAL CHANCES FOR BELOW, NEAR, 
OR ABOVE-NORMAL TEMPERATURES FORECAST ACROSS INTERIOR EASTERN ALASKA IS DUE TO 
DIFFERENCES AMONG DYNAMICAL MODEL GUIDANCE AND STATISTICAL TOOLS BASED ON LA 
NINA. THE DYNAMICAL MODELS OFFER WEAK PRECIPITATION SIGNALS ACROSS ALASKA WITH 
THE CALIBRATED NMME INDICATING INCREASED CHANCES FOR ABOVE-MEDIAN PRECIPITATION 
ACROSS THE ALEUTIANS AND WESTERN ALASKA. 


FORECASTER: BRAD PUGH


THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 
COMPLETE DECADES AS THE CLIMATE 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.



AN UPDATED MONTHLY OUTLOOK... FOR DEC WILL BE ISSUED ON WED NOVEMBER 30 2016


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

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