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PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EST SAT JAN 31 2009 30-DAY OUTLOOK DISCUSSION FOR FEBRUARY 2009 THE OVERALL THINKING FOR THE MONTHLY FORECAST HAS NOT CHANGED SUBSTANTIALLY IN THE UPDATE. FOR TEMPERATURE, THE EASTERN HALF OF THE CONUS IS EXPECTED TO SEE ABOVE-AVERAGE TEMPERATURES DURING THE FIRST PART OF THE MONTH AS INDICATED BY DYNAMICAL MODEL ENSEMBLE FORECASTS. BACKGROUND CLIMATE FACTORS - THE ONGOING LA NINA, ACTIVE MJO AND STATISTICAL TOOLS - SUPPORT WARMTH ACROSS MUCH OF THE SOUTH-CENTRAL AND SOUTHEAST US. PROBABILITIES OF ABOVE-AVERAGE TEMPERATURES ARE INCREASED IN THIS REGION FROM THE EARLIER FORECAST. THERE IS ALSO A SLIGHT EXPANSION IN ABOVE-AVERAGE TEMPERATURE PROBABILITIES ALONG THE NORTHERN EDGE OF THIS HIGHLIGHTED AREA FROM THE ORIGINAL FORECAST. ALTHOUGH THERE IS CONSIDERABLE SUPPORT FOR ABOVE-AVERAGE TEMPERATURES ACROSS THE NORTH-CENTRAL AND NORTHEAST US DURING THE FIRST HALF OF FEBRUARY, THIS REGION REMAINS HIGHLIGHTED EC. THE ANTICIPATED PHASES OF THE MJO DURING THE SECOND HALF OF THE MONTH WOULD FAVOR BELOW-AVERAGE TEMPERATURES ACROSS MUCH OF THE NORTHERN HALF OF THE CENTRAL AND EASTERN US. IN ADDITION, THE POTENTIAL FOR AN EXTENDED PERIOD OF NEGATIVE AO CONDITIONS LATER IN THE MONTH IN PART ASSOCIATED WITH THE RECENT SUDDEN STRATOSPHERIC WARMING FURTHER INCREASES THE UNCERTAINTY FOR THE MONTHLY MEAN TEMPERATURE FOR FEBRUARY IN THESE REGIONS. BELOW-AVERAGE TEMPERATURES REMAIN ACROSS THE PACIFIC NORTHWEST. SNOW COVER CONSIDERATIONS ARE NOW EXPECTED TO HAVE LITTLE IMPACT ACROSS PARTS OF THE ROCKIES SO THE LOBE OF BELOW-AVERAGE TEMPERATURES IN THIS AREA HAS BEEN REMOVED. TEMPERATURES ARE NOW EXPECTED TO BE CONSIDERABLY BELOW-AVERAGE ACROSS MUCH OF ALASKA DURING THE FIRST PART OF THE MONTH. FOR PRECIPITATION, THE AREA OF ABOVE-MEDIAN PRECIPITATION HAS BEEN EXPANDED TO COVER MUCH OF THE NORTH-CENTRAL US AND PARTS OF THE NORTHEAST US. DYNAMICAL MODEL ENSEMBLE PREDICTIONS INDICATE AN ACTIVE STORM TRACK DURING THE FIRST HALF OF THE MONTH ACROSS PARTS OF THE CENTRAL US ASSOCIATED WITH THE MEAN LONGWAVE TROUGH ANTICIPATED ACROSS THE WESTERN US. THIS IN COMBINATION WITH THE BACKGROUND CLIMATE CONDITIONS OF LA NINA INCREASE THE PROBABILITIES OF ABOVE-MEDIAN PRECIPITATION FROM THE OHIO VALLEY INTO THE GREAT LAKES. OTHER AREAS REMAINED GENERALLY UNCHANGED FROM THE EARLIER FORECAST. ** PREV DISCUSSION ** SEA SURFACE TEMPERATURE (SST) ANOMALIES IN THE EQUATORIAL PACIFIC HAVE CONTINUED TO DECREASE DURING THE LAST FEW WEEKS AND LA NINA CONDITIONS ARE PRESENT. THE SST DEPARTURES IN THE NINO 3.4 REGION (170W TO 120W AND 5N TO 5S) ARE NOW -1.1 DEGREES CELSIUS. SST FORECASTS FOR THE NINO 3.4 INDICATE THAT LA NINA CONDITIONS ARE EXPECTED TO CONTINUE THROUGH FEBRUARY 2009. ATMOSPHERIC CONDITIONS IN THE TROPICAL PACIFIC OCEAN ARE ALSO CONSISTENT WITH LA NINA. SUPPRESSED CONVECTION CONTINUES NEAR THE DATE LINE AND LOW-LEVEL EASTERLY AND UPPER-LEVEL WESTERLY WIND ANOMALIES ARE EVIDENT IN 30 DAY AVERAGES OVER THE PACIFIC. THE MJO HAS STRENGTHENED IN RECENT DAYS WITH THE ENHANCED CONVECTIVE PHASE LOCATED IN THE WESTERN HEMISPHERE AND IT IS ALSO CONSIDERED IN THE FEBRUARY FORECAST. THE MONTHLY FORECAST PLACES CONSIDERABLE WEIGHT ON LA NINA COMPOSITES DUE TO THE RECENT MARKED DECREASE IN PACIFIC SSTS AND CIRCULATION PATTERNS AND TEMPERATURE AND PRECIPITATION ANOMALIES ACROSS THE US AVERAGED OVER THE LAST 30 DAYS THAT ARE CONSISTENT WITH LA NINA. THERE IS LARGE UNCERTAINTY IN THE PREDICTION OF THE MJO AT A LEAD TIME OF TWO WEEKS, HOWEVER, IF THE MJO CONTINUES TO STRENGTHEN AND PROPAGATE ITS ENHANCED CONVECTIVE PHASE IS EXPECTED TO BE LOCATED ACROSS THE EASTERN INDIAN OCEAN, INDONESIA AND FAR WESTERN PACIFIC DURING A SUBSTANTIAL PORTION OF FEBRUARY – POTENTIALLY REINFORCING THE BASE LA NINA CIRCULATION. THERE IS GOOD AGREEMENT AMONGST THE FORECAST TOOLS FOR TEMPERATURE – BOTH STATISTICAL AND DYNAMICAL. THE CCA, OCN, SMLR, AND CFS ALL POINT TO ABOVE-AVERAGE TEMPERATURES FOR MUCH OF THE LOWER HALF OF THE CONTINENTAL US FROM PARTS OF THE SOUTHWEST TO THE MID-ATLANTIC. LA NINA AND MJO COMPOSITES ALSO SUPPORT ABOVE-AVERAGE TEMPERATURES IN THIS REGION. THE CCA FORECAST INDICATES ADDITIONAL WARMTH ACROSS THE FAR NORTHERN PLAINS BUT THIS WAS DISCOUNTED DUE TO CONFLICTING COLD SIGNALS FROM LA NINA COMPOSITES AND THE CFS AS WELL AS EXTENSIVE SNOW COVER. COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR PORTIONS OF THE NORTHWEST US CONSISTENT WITH LA NINA COMPOSITES, THE CCA TOOL, CFS, AND BELOW AVERAGE SSTS ALONG THE WEST COAST. AN EXTENSION OF COLD IS DEPICTED ACROSS PARTS OF THE INTERIOR ROCKIES IN PART DUE TO CONSIDERABLE SNOW COVER. THE TEMPERATURE TOOLS CONFLICTED FOR ALASKA SO EC IS INDICATED. THE PRECIPITATION FORECAST ALSO RELIED SIGNIFICANTLY ON LA NINA COMPOSITES BUT INFORMATION FROM THE CCA AND CFS WERE ALSO CONSULTED. BELOW-MEDIAN PRECIPITATION IS FORECAST ACROSS MUCH OF THE SOUTHEAST US FROM THE GULF COAST TO THE SOUTHERN MID-ATLANTIC DUE TO LA NINA COMPOSITES, THE CCA TOOL, THE CFS AND STRONG RECENT TRENDS. ABOVE-MEDIAN PRECIPITATION IS FORECAST FOR THE PACIFIC NORTHWEST AND OHIO VALLEY REGIONS BASED ON THE RELATIONSHIP WITH LA NINA CONDITIONS FOR THESE TWO REGIONS. THE PRECIPITATION TOOLS FOR ALASKA ALSO CONFLICTED SO EC IS INDICATED. FORECASTER: JON GOTTSCHALCK NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES). THE NEXT MONTHLY OUTLOOK...FOR MARCH 2009...WILL BE ISSUED ON THU FEB 19 2009 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD. $$
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