PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300PM EST FRIDAY NOV 30 2012 30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2012 THIS MONTHLY UPDATE COMBINES INFORMATION FROM EXTENDED RANGE WEATHER FORECASTS FOR CONDITIONS DURING THE FIRST HALF OF DECEMBER WITH INFORMATION RELATING TO LONGER TERM EXPECTED CLIMATIC ANOMALIES AS REFLECTED IN THE DECEMBER OUTLOOK RELEASED IN MID-NOVEMBER. SEA SURFACE TEMPERATURE (SST) ANOMALIES IN THE CENTRAL PACIFIC OCEAN NEAR THE EQUATOR TRENDED DOWNWARD DURING THE LAST HALF OF NOVEMBER, BUT REMAIN SLIGHTLY POSITIVE. THIS IS IN LINE WITH SST PREDICTIONS AVAILABLE AT THE TIME THE MID-MONTH MONTHLY OUTLOOK WAS RELEASED, THUS EXPECTED CLIMATIC INFLUENCE RELATED TO THE TROPICAL PACIFIC CIRCULATION REMAINS THE SAME AS EXPECTED IN THE EARLIER OUTLOOK. THE TEMPERATURE FORECAST FROM THE CFS ENSEMBLES REMAIN FAIRLY CONSISTENT WITH EARLIER EXPECTATIONS. MUCH OF CONUS IS EXPECTED TO BEGIN THE MONTH WITH ABOVE NORMAL TEMPERATURES, AS FORECAST BY GFS AND OTHER MODELS. THESE SHORT TERM WEATHER INDICATORS ARE REFLECTED IN THE CFS MONTHLY FORECAST FOR DECEMBER, WHICH IS THE PRIMARY TOOL ON WHICH THIS UPDATED FORECAST IS BASED. THE CFS CONTINUES TO SUGGEST BELOW NORMAL TEMPERATURES FOR ALASKA, WHICH IS IN LINE WITH OBSERVED ANOMALIES IN THE LAST HALF OF NOVEMBER, THUS CONFIDENCE IN BELOW NORMAL TEMPERATURES FOR ALASKA HAVE INCREASED, AND THE ABOVE NORMAL TEMPERATURES INDICATED FOR NORTHERN ALASKA ON THE PREVIOUS OUTLOOK HAVE BEEN REMOVED. AN EXPECTED WARM START TO THE MONTH FOR MUCH OF THE CONUS RESULTS IN ELEVATED CHANCES FOR ABOVE NORMAL TEMPERATURES FOR MUCH OF THE SOUTHERN AND CENTRAL CONUS. THE CFS CONTINUES TO SUGGEST A SHARP GRADIENT IN TEMPERATURE ANOMALIES IN THE NORTHERN CONUS, TRANSITIONING FROM ABOVE TO BELOW NORMAL TEMPERATURES NEAR THE CANADIAN BORDER. THIS SUGGESTS A LARGE UNCERTAINTY FOR THE REGION WITH EQUAL CHANCES FOR THE MONTHLY MEANS IN THE AREA TO FINISH ABOVE, NEAR, OR BELOW LONG TERM AVERAGES. BELOW NORMAL SSTS NEAR THE SOUTHEASTERN U.S. ELEVATE CHANCES FOR BELOW NORMAL TEMPERATURES NEAR FLORIDA. THE EARLY PART OF THE MONTH APPEARS STORMY FOR THE PACIFIC NORTHWEST, INCREASING CHANCES FOR ABOVE MEDIAN PRECIPITATION AMOUNTS FOR NORTHERN CALIFORNIA, MUCH OF THE PACIFIC NORTHWEST, AND THE NORTHERN ROCKIES. THE CFS FORECAST FOR DECEMBER PRECIPITATION IN OTHER AREAS REMAINS MOSTLY CONSISTENT WITH THE FORECAST ISSUED IN MID-MONTH. THERE ARE SUGGESTIONS THAT THE MAIN STORM TRACK MAY BE A BIT FURTHER NORTH OVER THE EASTERN CONUS THAN EXPECTED ON THE PREVIOUS OUTLOOK. THIS RESULTS IN A NORTHWARD SHIFT OF THE AREA OF ABOVE MEDIAN PRECIPITATION FOR THE EAST-CENTRAL CONUS INDICATED ON THE EARLIER OUTLOOK TO A POSITION CENTERED OVER THE LOWER GREAT LAKES. AN EXPECTED DRY START TO THE MONTH, TOGETHER WITH SOME SUGGESTION FROM THE CFS FOR CONTINUED DRY CONDITIONS, RESULT IN ENHANCED ODDS FOR BELOW MEDIAN PRECIPITATION IN AND NEAR TEXAS AND FLORIDA. PREVIOUS DISCUSSION FOR DECEMBER 2012 ISSUED IN MID-NOVEMBER 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. THE NEXT MONTHLY OUTLOOK...FOR JAN ... WILL BE ISSUED ON THU DEC 20 2012 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$