PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EST THURSDAY NOV 15 2012

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2012

OCEANIC AND ATMOSPHERIC INDICATORS CONTINUED TO SUGGEST ENSO NEUTRAL CONDITIONS 
DURING THE FIRST HALF OF NOVEMBER.  SEA SURFACE TEMPERATURE (SST) ANOMALIES 
REMAINED FAIRLY STEADY ACROSS MUCH OF THE CENTRAL PACIFIC OCEAN IN THE PAST 
MONTH OR SO. ANOMALIES OF BETWEEN 0 AND +0.5 DEGREES C PREDOMINATE THROUGHOUT 
THE EAST CENTRAL EQUATORIAL PACIFIC OCEAN, WHILE ANOMALIES WEST OF THE DATE 
LINE ALONG THE EQUATOR ARE MOSTLY BETWEEN +0.5 AND +1.5 C.  ATMOSPHERIC 
OBSERVATIONS OVER THE TROPICAL PACIFIC OCEAN REMAINED CONSISTENT WITH ENSO 
NEUTRAL CONDITIONS, WITH LARGE SCALE WIND AND CONVECTION MOSTLY NEAR THEIR 
CLIMATOLOGICAL NORMALS AS OF LATE OCTOBER.  SST PREDICTION FROM STATISTICAL AND 
DYNAMICAL MODELS INDICATE A CONTINUATION OF WEAKLY POSITIVE ANOMALIES ALONG THE 
EQUATOR IN THE EAST-CENTRAL PACIFIC THROUGH THE END OF THE YEAR, SUGGESTING 
THAT ENSO NEUTRAL CONDITIONS WILL PREVAIL THROUGH DECEMBER, 2012.  

THE TEMPERATURE OUTLOOK FOR DECEMBER INDICATES ELEVATED CHANCES FOR 
ABOVE-NORMAL MEAN TEMPERATURES FOR THE SOUTHWESTERN U.S., THE SOUTHERN ROCKIES, 
MOST OF TEXAS, AND PARTS OF THE GULF COAST STATES.  BELOW NORMAL TEMPERATURES 
ARE FAVORED FOR PORTIONS OF SOUTHERN ALASKA, INCLUDING THE ALASKAN PANHANDLE, 
AND IN PARTS OF THE NORTHERN GREAT PLAINS AND UPPER MISSISSIPPI VALLEY.  THIS 
FORECAST IS SUPPORTED BY THE NCEP CFS MODEL AS WELL AS ENSEMBLE MEANS FROM THE 
NATIONAL MULTI-MODEL ENSEMBLE (NMME) AND INTERNATIONAL MULTI-MODEL ENSEMBLE.  
THE UPPER LEVEL CIRCULATION PATTERN OVER THE NORTH PACIFIC AND WESTERN NORTH 
AMERICA PREDICTED BY THE NCEP CFS MODEL RESEMBLES COMPOSITES FOR THE NEGATIVE 
PHASE OF THE PACIFIC DECADAL OSCILLATION (PDO).  THE TEMPERATURE PATTERN 
PREDICTED BY THE CFS AND THE NMME ALSO CORRESPONDS WELL WITH NEGATIVE PDO 
COMPOSITES.  THIS, TOGETHER WITH THE FACT THAT THE OBSERVATIONS SO FAR THIS 
FALL ARE ALSO SUGGESTIVE OF A NEGATIVE PDO PHASE, GIVES SOME ADDED CONFIDENCE 
IN THE CLIMATE MODELS FORECASTS.  IT IS WORTH NOTING THAT THE TEMPERATURE 
PATTERN PREDICTED BY THE MODELS WOULD NOT BE SUPPORTED BY TELECONNECTIONS TO 
THE WEAKLY POSITIVE EQUATORIAL PACIFIC SST ANOMALIES PREDICTED BY MOST MODELS.
          
THERE ARE FEW CONSISTENT SIGNALS AMONG THE TOOLS FOR DECEMBER PRECIPITATION 
ANOMALIES.  THE CLIMATE MODEL PREDICTIONS DO NOT SHOW THE SAME CONSISTENCY WITH 
THE DECEMBER OBSERVATIONS FOR NEGATIVE PDO YEARS AS THEY DO FOR TEMPERATURES.  
THE CFS INDICATES BELOW MEDIAN PRECIPITATION AMOUNTS FOR PARTS OF THE SOUTHERN 
COAST OF ALASKA AND FOR THE ALASKAN PANHANDLE, WHICH IS CONSISTENT WITH A 
NEGATIVE PDO.  OTHERWISE THE CFS AND OTHER MODELS SHOW CONFLICTING INDICATIONS, 
SUGGESTING THAT CLIMATOLOGICAL ODDS FOR PRECIPITATION AMOUNTS MAY BE THE SAFEST 
CHOICE.  THE EXCEPTION BEING A WEAK CONSENSUS AMONG THE NMME CLIMATE MODELS FOR 
ABOVE MEDIAN PRECIPITATION AMOUNTS FOR THE MIDDLE MISSISSIPPI, TENNESSEE AND 
OHIO RIVER VALLEYS.  

THE MAIN FACTORS WHICH USUALLY INFLUENCE THE MONTHLY CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE ENSO. IMPACTS OF THESE EVENTS ARE 
SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM THREE OR MORE DECADES INTO 
EL NINO, NEUTRAL AND LA NINA SETS, AVERAGING EACH SEPARATELY, AND THEN 
COMPUTING ANOMALIES. THESE ARE CALLED "COMPOSITES" AND USED AT TIMES TO 
SUBJECTIVELY MODIFY THE FORECAST.
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST 
RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN 
LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY 
1981-2010).
3) THE TROPICAL 30-60 DAY OSCILLATION - CALLED THE MADDEN JULIAN OSCILLATION 
(MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), 
AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE 
ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO 
HAVE LOW PREDICTABILITY.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE 
VARIABILITY AFFECTING THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN 
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO.
6) PERSISTANTLY DRY OR WET SOILS IN THE SPRING AND SUMMER AND SNOW AND ICE 
COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS 
AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM.
7) STATISTICAL FORECAST MODELS - CANONICAL CORRELATION ANALYSIS (CCA), 
SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOG (CA), AND 
ENSEMBLE CCA (ECCA).
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM 
VERSION 2 (CFS) AND FOR ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE 
FORECAST SYSTEM (GEFS). THE EARLIER VERSION OF THE CFS MODEL WAS DISCONTINUED 
AS OF OCTOBER, 2012. AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL 
ENSEMBLE (NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED.


FORECASTER: DAVID UNGER


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 FRI NOVEMBER 30 2012


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

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