PROGNOSTIC DISCUSSION FOR UPDATED MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EST SAT APR 30 2005

30-DAY OUTLOOK DISCUSSION FOR MAY 2005
                                                                               .
SST ANOMALIES ALONG THE EQUATOR IN THE PACIFIC HAVE DECREASED SINCE THE 
BEGINNING OF THE YEAR... WITH THE AREA NEAR AND WEST OF THE DATE LINE HAVING 
DECREASED IN MAGNITUDE TO BARELY 0.5 DEGREE C ABOVE NORMAL IN RECENT WEEKS.  
HOWEVER... A NEW BUT SMALL AREA OF GREATER THAN 1 DEGREE C ABOVE NORMAL 
SST HAS DEVELOPED IN THE EASTERN EQUATORIAL PACIFIC BETWEEN 95W AND 120W...
PROBABLY AS A RESULT OF THE EASTWARD MOVEMENT OF A STRONG KELVIN WAVE ALONG 
THE THERMOCLINE ABOUT 50 TO 100 M BENEATH THE SURFACE IN THAT AREA. LATEST 
OBSERVATIONS SHOW THAT THE ABOVE NORMAL SUBSURFACE TEMPERATURES ARE WEAKENING 
AS THE KELVIN WAVE BEGINS TO SHOAL OVER THE EASTERN PACIFIC.  ALTHOUGH THE 
AVERAGE SST ANOMALIES HAVE RETURNED TO POSITIVE VALUES IN THE NINO 3 AND NINO 
3.4 AREAS FOLLOWING A BRIEF EXCURSION INTO NEGATIVE TERRITORY DURING LATE 
FEBRUARY AND MARCH... EXPECTATIONS ARE THAT THE ENSO EPISODE OF THE PAST FEW 
SEASONS WILL CONTINUE TO GRADUALLY WEAKEN WITHIN THE NEXT FEW MONTHS... 
AND THEREFORE ENSO IS NOT EXPECTED TO INFLUENCE THE CLIMATE DURING MAY OVER 
NORTH AMERICA. 

THE TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON A SUBJECTIVE BLEND OF 
THE MONTHLY STATISTICAL TOOLS AND MODEL FORECASTS... WITH SOMEWHAT MORE 
EMPHASIS OF THE MEDIUUM RANGE INDICATIONS FROM THE NCEP GFS MODEL FOR THIS 
UPDATED MONTHLY FORECAST.  DUE TO SIGNIFICANT CHANGES IN THE ATMOSPHERIC 
CRIRCULATION PREDICTED TO OCCUR BETWEEN THE FIRST AND SECOND WEEKS OF THE 
UPCOMING MONTH... THE CURRENT MODEL INDICATIONS ARE NOT TOO HELPFUL FOR THE 
TEMPERATURE FORECAST IN MOST AREAS OF THE EASTERN AND CENTRAL CONUS.  
HOWEVER... BOTH OF THE FIRST TWO WEEKS LOOK WARM OVER MOST OF ALASKA IN 
AGREEMENT WITH THE LONG LEAD STATISTICAL TOOLS... SO PROBABILITIES FOR ABOVE 
NORMAL TEMPERATURTES WERE INCREASED SLGHTLY THERE.  ALSO... PERSISTENT RIDGING 
OVER THE PACIFIC NORTHWEST REINFORCES INDICATIONS FROM THE STATISTICAL TOOLS 
FOR WARMTH IN THAT AREA.  ALTHOUGH THE FIRST WEEK OF MAY IS PREDICTED TO BE 
ABNORMALLY COOL OVER THE CENTRAL AND EASTERN U.S. ... MODELS HAVE BEEN QUITE 
CONSISTENT IN BUILDING A RIDGE DURING THE SECOND WEEK... WHICH WOULD AGREE 
WITH SOME OF THE INDICATIONS FROM THE STATISTICAL TOOLS FOR ABOVE NORMAL 
TEMEPRATURES IN THE CENTRAL PART OF THE NATION.   INDICATIONS FOR BELOW 
NORMAL TEMPERATURES OVER THE EASTERN GULF STATES AND FLORIDA FROM THE CONTRUCTED 
ANALOG SOIL MOISTURE (CAS) TOOL ARE REINFORCED BY CURRENT AND PREDICTED HEAVY 
RAINS AND BELOW NORMAL SSTS IN THAT AREA.  ABOVE NORMAL TEMPERATURES WERE 
FORECAST ONLY IN THAT PART OF THE INTERIOR SOUTHWEST THAT HAD THE STRONGEST OCN 
SIGNAL FOR WARMTH AND RELATIVELY WEAK SIGNALS FOR COLD FROM THE CFS MODEL.  
BELOW NORMAL TEMPERATURES WERE INTROUCED OVER NORTHERN AND CENTRAL CALIFORNIA 
DUE TO MODEL FORECASTS OF A RATHER STRONG TROUGH APPORACHING THE COAST DURING 
THE SECOND WEEK OF MAY... AND INDICATIONS FOR FREQUENT PRECIPITATION DURING 
BOTH WEEKS.  ALSO... THERE IS NO CONTRARY TREND SIGNAL FOR WAMRTH IN THAT AREA.

THE  PRECIPITATION OUTLOOK FOR MAY SHOWS THREE AREAS OF ABOVE MEDIAN 
PRECIPITATION.  THE ONE CENTERED OVER THE UPPER MISSISSIPPI VALLEY THAT WAS 
FAVORED BY A CONSENSUS OF THE MODELS WHEN THE LONG-LEAD FORECAST FOR MAY WAS 
PREPARED STILL LOOKS GOOD FROM DEVLEOPMENTS PREDICTED DURING THE SECOND WEEK 
OF THE MONTH... ALTHOUGH THE FIRST WEEK WILL BE RATHER DRY.   AN AREA OF 
ABOVE MEIDAN PRECIPITATION WAS INTRODUCED OVER NORTHERN AND CENTRAL CALIFORNIA 
DUE TO STRONG AND CONSISTENT INDICATIONS THAT A VIGOROUS TROUH WILL APPROACH 
THE AREA DURING THE SECOND WEEK OF THE MONTH.  SINCE CLIMATOLOGICAL VALUES 
ARE QUITE SMALL THIS LATE IN THE SEASON... IT WILL NOT TAKE MUCH TO MAKE 
ABOVE MEDIAN TOTALS FOR THE MONTH.  FINALLY... AN AREA OF ABOVE MEDIAN 
RAINFALL IS BEING PREIDCTED FOR THE EAST GULF STATES AND FLORIDA DUE TO 
MODEL FORECASTS OF ADDITIONAL EPISODES OF HEAVY PRECIPITATION DURING THE 
FIRST WEEK OF THE MONTH... IN ADDITION TO THE CURRENT ONE WHICH WILL BE 
WINDING DOWN EXCEPT FOR OVER FLORIDA WHEN THE NEW MONTH BEGINS.  AS THAT 
AREA DOES NOT REALLY GET INTO ITS RAINY SEASON UNTIL JUNE... IT IS BELIEVED 
THAT WITH SUCH A WET START IT WILL NOT TAKE MUCH MORE PRECIPITATION TO HAVE 
ABOVE MEDIAN TOTALS FOR THE MONTH AS A WHOLE.  SINCE THERE WERE NO SIGNIFIANCT 
CONSISTENT SIGNALS FROM EITHER MODELS OR STATISTCAL TOOLS FOR THE ALASKA 
PRECIPITATION FORECAST... THE ENTIRE STATE WAS LEFT AS EC.

  
FORECASTER: A. J. WAGNER 


NOTES -  AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILTIES) ARE NOW LABELED EC (EQUAL CHANCES).  
  
THE NEXT 0.5-MONTH LEAD-TIME MONTHLY OUTLOOK - FOR JUNE - WILL BE ISSUED 
THU MAY 19 2005.
  
  
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.


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