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PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT FRI JUL 31 2009 30-DAY OUTLOOK DISCUSSION FOR AUGUST 2009 EL NINO CONDITIONS CONTINUE ACROSS THE EQUATORIAL PACIFIC OCEAN WITH WEEKLY AVERAGE SEA SURFACE TEMPERATURE (SST) ANOMALIES BETWEEN +0.5 AND +1.5 DEGREES CELSIUS (C). DURING THE LAST MONTH CONVECTION HAS BEEN ENHANCED NEAR 180W LONGITUDE WHILE LOW LEVEL WESTERLY WIND ANOMALIES HAVE BEEN OBSERVED JUST TO THE WEST OF THIS AREA ALONG THE EQUATOR. NUMERICAL WEATHER PREDICTION MODELS INCLUDING THE NCEP GLOBAL FORECAST SYSTEM (GFS) HAVE BEEN CONSULTED IN CREATING THE ZERO-LEAD AUGUST FORECAST, ALONG WITH THE LATEST AUGUST FORECASTS FROM THE NCEP CLIMATE FORECAST SYSTEM (CFS). THE MONTHLY FORECAST STATISTICAL TOOLS AND EL NINO COMPOSITES WERE ALSO CONSULTED. A TROUGH IS FORECAST TO BE JUST OFF OF THE US PACIFIC NORTHWEST COAST LEADING TO FAVORABLE CONDITIONS FOR PRECIPITATION IN THIS REGION FOR THE FIRST TWO WEEKS OF AUGUST. CLIMATOLOGICALLY, THIS AREA RECEIVES VERY LITTLE PRECIPITATION DURING THE MONTH OF AUGUST, SUCH THAT ACCUMULATED PRECIPITATION EXCEEDING ONLY 1-5 MILLIMETERS WILL RESULT IN VERIFICATION OF THE ABOVE MEDIAN TERCILE. FORECASTS FOR THE FIRST TWO WEEKS OF AUGUST ALSO INDICATE GREATER THAN CLIMATOLOGICAL PROBABILITIES FOR BELOW MEDIAN ACCUMULATED PRECIPITATION IN THE NORTH AMERICAN MONSOON (NAM) REGION. THIS FORECAST IS SOMEWHAT CONSISTENT WITH CURRENT EL NINO CONDITIONS OVER THE TROPICAL PACIFIC AND THEREFORE MAY PERSIST THROUGH THE MONTH OF AUGUST. THOUGH THE NAM PRECIPITATION FORECAST IS LESS CERTAIN FOR THE SECOND HALF OF AUGUST, TOTAL PRECIPITATION FOR THE MONTH IS MORE LIKELY TO BE IN THE BELOW MEDIAN TERCILE. THE AREA OF ENHANCED PROBABILITIES FOR ABOVE MEDIAN ACCUMULATED PRECIPITATION FROM THE CENTRAL PLAINS TO THE MIDWEST IS CONSISTENT WITH MODEL FORECASTS FOR THE EARLY PART OF AUGUST AND RECENT CFS MONTHLY FORECASTS. THE ZERO-LEAD TEMPERATURE OUTLOOK FOR AUGUST HAS CHANGED LITTLE FROM THE HALF-MONTH LEAD FORECAST WITH SOME SLIGHT MODIFICATIONS FOLLOWING THE NWP MODEL FORECASTS AND TWO-WEEK EXTENDED RANGE ENSEMBLE MODEL FORECASTS. THE PROBABILITY OF ABOVE NORMAL MEAN AUGUST TEMPERATURES IS ENHANCED FOR EASTERN ALASKA AND THE ALASKAN PANHANDLE WHERE A RIDGE IS EXPECTED TO PERSIST FOR AT LEAST THE EARLY PART OF THE MONTH. THIS FORECAST IS FURTHER SUPPORTED BY THE MOST RECENT CFS AUGUST FORECASTS. THE AREA OF ENHANCED PROBABILITIES FOR BELOW NORMAL MEAN MONTHLY TEMPERATURES OVER THE US MIDWEST HAS BEEN MOVED SLIGHTLY NORTH AND EAST FROM THE PREVIOUS OUTLOOK. THE PROBABILITY OF ABOVE NORMAL TEMPERATURES HAS BEEN INCREASED FOR THE NAM REGION WHERE CONDITIONS ARE EXPECTED TO BE DRIER THAN NORMAL. PROBABILITIES FOR ABOVE NORMAL TEMPERATURES HAVE BEEN DECREASED TO NEAR CLIMATOLOGY FOR CALIFORNIA. THE TEXT FROM THE ORIGINAL HALF-MONTH LEAD AUGUST FORECAST RELEASED ON JULY 16TH FOLLOWS: EQUATORIAL SEA SURFACE TEMPERATURE (SST) ANOMALIES IN THE CENTRAL PACIFIC OCEAN CURRENTLY RANGE FROM POSITIVE 0.5 TO OVER 1 DEGREES CELSIUS (C) FROM ABOUT 160E LONGITUDE TO THE SOUTH AMERICAN COAST. THERE IS A RESERVOIR OF MODERATELY WARM WATER (1 TO 3 C ABOVE NORMAL) BENEATH THE SURFACE ALONG THE EQUATOR, WITH MAXIMUM ANOMALIES SLOPING UPWARD FROM A DEPTH OF ABOUT 150 METERS AT 160E TO A DEPTH OF ABOUT 50 METERS NEAR THE SOUTH AMERICAN COAST. BASIN-WIDE EQUATORIAL UPPER OCEAN HEAT CONTENT TYPICALLY PEAKS AS AN EL NINO EVENT DEVELOPS. BASIN-WIDE (180-100W LONGITUDE) UPPER OCEAN (0-300 M) HEAT CONTENT HAS BEEN INCREASING SINCE THE START OF 2009, WITH THE CURRENT BASIN-WIDE MEAN UPPER OCEAN TEMPERATURE ANOMALY BETWEEN POSITIVE 1 AND 1.5 C. WESTERLY WIND ANOMALIES ARE CURRENTLY PRESENT OVER THE WESTERN AND EASTERN PACIFIC. EL NINO CONDITIONS ARE PRESENT DURING JULY WITH EL NINO CONDITIONS EXPECTED TO CONTINUE TO DEVELOP DURING AUGUST. ENSO COMPOSITES WERE THEREFORE CONSULTED FOR THE AUGUST FORECASTS, THOUGH EL NINO HAS ONLY WEAK IMPACTS FOR NORTH AMERICA DURING THE SUMMER. THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR AUGUST HAVE BEEN CONSTRUCTED PRIMARILY USING LONG LEAD MONTHLY STATISTICAL TOOLS, INCLUDING THE OCN TREND, CCA AND SMLR; LOCAL SSTS ALONG COASTAL AREAS; AND THE CFS COUPLED OCEAN-ATMOSPHERE DYNAMICAL MODEL MONTHLY TEMPERATURE AND PRECIPITATION PREDICTIONS. THE ZERO LEAD MONTHLY UPDATE ON JULY 31, 2009 WILL INCORPORATE INFORMATION FROM THE SHORT RANGE NUMERICAL WEATHER PREDICTION MODELS AND THE LATEST CFS MONTHLY PREDICTIONS. SST ANOMALIES NEAR THE US WEST COAST HAVE RETURNED TO BELOW NORMAL FROM NORTHERN CALIFORNIA NORTH TO WASHINGTON DURING THE PAST TWO WEEKS, WHILE SST ANOMALIES AROUND MOST OF ALASKA'S COASTS ARE NOW ABOVE NORMAL. ALONG THE US EAST COAST AND THE GULF OF MEXICO SST ANOMALIES HAVE RETURNED TO NEAR NORMAL IN THE LAST WEEK AFTER ABOUT TWO WEEKS AT ABOVE NORMAL. THE AUGUST MONTHLY OUTLOOK INDICATES INCREASED PROBABILITIES OF ABOVE NORMAL MONTHLY MEAN TEMPERATURES IN MUCH OF THE WESTERN US FROM WESTERN ARIZONA EXTENDING NORTHWEST TO THE COAST OF WASHINGTON. SUPPORT FOR THIS FORECAST IS DERIVED FROM THE TEMPERATURE TRENDS FROM THE OCN, WITH SUPPORT FROM THE SMLR AND CCA FOR PARTS OF THE SOUTHWEST, AND FROM THE CFS FOR PARTS OF NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST. INCREASED PROBABILITIES OF ABOVE NORMAL MONTHLY MEAN TEMPERATURES ARE ALSO INDICATED FROM EASTERN TEXAS ALONG THE GULF COAST STATES INTO FLORIDA. ALL OF THE STANDARD STATISTICAL TOOLS, CCA, OCN AND SMLR, AGREE IN THIS REGION TO SOME EXTENT, WITH THE CFS INDICATING A HIGH PROBABILITY FOR ABOVE NORMAL TEMPERATURES. CURRENT DROUGHT CONDITIONS FROM TEXAS TO LOUISIANA ALSO INCREASE THE PROBABILITIES OF ABOVE NORMAL TEMPERATURES FOR THIS AREA. THE INCREASED PROBABILITY OF ABOVE NORMAL TEMPERATURES FOR SOUTHWESTERN REGIONS OF ALASKA IS RELATED TO THE TEMPERATURE TREND, INDICATED IN THE OCN AND CCA, AND IN AGREEMENT WITH RECENTLY WARMER COASTAL WATERS. AN INCREASED PROBABILITY OF BELOW NORMAL MONTHLY MEAN TEMPERATURES FOR THE CENTRAL AND UPPER MISSISSIPPI VALLEY IS SUGGESTED BY THE CFS MONTHLY PREDICTION AND THE CCA AND SMLR TOOLS. EL NINO COMPOSITES INDICATE ONLY WEAK TEMPERATURE SIGNALS FOR AUGUST. THE INCREASED VARIABILITY AND LOW PREDICTABILITY OF PRECIPITATION DURING THE WARM SEASON RESULTS IN LIMITED COVERAGE IN THE AUGUST PRECIPITATION OUTLOOK. AN INCREASED PROBABILITY OF MONTHLY PRECIPITATION AMOUNTS IN THE ABOVE MEDIAN TERCILE IS FORECAST FOR AN AREA FROM THE CENTRAL ROCKY MOUNTAINS AND HIGH PLAINS SOUTHEASTWARD INTO THE CENTRAL PLAINS. THIS FORECAST IS SUPPORTED PRIMARILY BY THE CFS MONTHLY PRECIPITATION, THE SMLR AND THE OCN PRECIPITATION TREND. A GREATER LIKELIHOOD OF BELOW NORMAL PRECIPITATION AMOUNTS FOR AUGUST IS GIVEN FOR THE WESTERN GULF COAST, WHERE SOIL MOISTURE CONDITIONS ARE CURRENTLY EXTREMELY DRY. THIS IS SUPPORTED BY THE CFS MONTHLY PREDICTION AND EL NINO COMPOSITES. FORECASTER: DAN COLLINS NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES). THE NEXT MONTHLY OUTLOOK...FOR SEPTEMBER 2009...WILL BE ISSUED ON THU AUG 20 2009 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD. $$
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