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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