PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT WED APR 30 2008

30-DAY OUTLOOK DISCUSSION FOR MAY 2008

LA NINA CONDITIONS CONTINUE THROUGHOUT THE TROPICAL PACIFIC.  BELOW AVERAGE SEA 
SURFACE TEMPERATURES (SSTS) ARE OBSERVED ACROSS THE CENTRAL EQUATORIAL PACIFIC. 
 SSTS MORE THAN 1 DEGREE CENTIGRADE BELOW AVERAGE WERE OBSERVED BETWEEN 160E 
AND 140W.  THE LATEST WEEKLY NINO 3.4 REGION INDEX VALUE IS NOW -0.8 DEGREES C 
WHICH REPRESENTS A WEAKENING OF THE NEGATIVE DEPARTURES FROM TWO WEEKS AGO BY 
0.1 DEGREES.  THE UPPER-OCEAN HEAT CONTENT CONTINUED TO RISE AS WELL, AND 
ANOMALIES NOW AVERAGE SLIGHTLY POSITIVE EAST OF THE DATE LINE.  LOW LEVEL 
EQUATORIAL EASTERLY WINDS CONTINUE TO BE STRONGER THAN AVERAGE ACROSS THE 
CENTRAL EQUATORIAL PACIFIC... STRONGER THAN AVERAGE UPPER LEVEL WESTERLY WINDS 
ALSO CONTINUE, AND CONVECTION HAS BEEN SUPPRESSED OVER THE CENTRAL PACIFIC.  
COLLECTIVELY, THESE ATMOSPHERIC AND OCEANIC CONDITIONS ARE CONSISTENT WITH 
MATURE LA NINA CONDITIONS.  SST FORECASTS FROM THE CFS AND A SUITE OF OTHER 
STATISTICAL AND DYNAMICAL MODELS INDICATE THAT LA NINA SHOULD CONTINUE THROUGH 
MJJ OR POSSIBLY JJA.  

INTRASEASONAL (MJO) ACTIVITY WAS RATHER PERSISTENT THROUGH MARCH, BUT IS 
CURRENTLY AT NEGLIGIBLE LEVELS.  THEREFORE, THE MJO DOES NOT HAVE A SIGNIFICANT 
INFLUENCE ON THIS MONTHLY FORECAST.  BECAUSE THIS UPDATE IS A ZERO-LEAD 
FORECAST, MUCH OF THE INPUT TO IT IS WEIGHTED TOWARD DYNAMICAL MODEL FORECASTS 
VALID FOR THE WEEK 2 TIME PERIOD, AND EVEN EARLIER IN THE CASE OF PRECIPITATION.

THE TEMPERATURE OUTLOOK FOR MAY FAVORS ABOVE AVERAGE TEMPERATURES ALONG 
SECTIONS OF THE GULF COAST, AND IN MUCH OF ALASKA.  BELOW-AVERAGE TEMPERATURES 
ARE MOST LIKELY FROM THE PACIFIC NORTHWEST EASTWARD THROUGH THE CENTRAL AND 
NORTHERN GREAT PLAINS TO THE WESTERN AND CENTRAL GREAT LAKES.  GFS, AND TO A 
LESSER DEGREE, CFS, SMLR, CCA AND LA NINA COMPOSITES CONTRIBUTE TO THIS 
FORECAST PATTERN.  ELSEWHERE, EQUAL CHANCES OF BELOW-, NEAR-, AND ABOVE NORMAL 
TEMPERATURE ARE FORECAST.

THE PRECIPITATION FORECAST FOR MAY CALLS FOR ABOVE-MEDIAN PRECIPITATION IN 
WESTERN SECTIONS OF ALASKA, BASED ON THE GFS.  ABOVE-MEDIAN RAINFALL IS ALSO 
EXPECTED FOR THE GREAT LAKES, WISCONSIN, MINNESOTA, AND CENTRAL AND EASTERN 
SECTIONS OF THE DAKOTAS, BASED ON THE GFS.  ABOVE-MEDIAN RAINFALL IN THE 
NORTHERN ROCKIES IS FROM HEAVY PRECIPITATION FORECASTS FROM DAYS 1 AND 2 OF THE 
FORECAST PERIOD.  SUB-MEDIAN RAINFALL IS EXPECTED FOR THE SOUTHWEST, NORTHERN 
CALIFORNIA AND WESTERN SECTIONS OF THE NORTHWEST, AND FOR EASTERN SECTIONS OF 
ALASKA.  ELSEWHERE, EQUAL CHANCES OF BELOW-, NEAR-, AND ABOVE NORMAL 
PRECIPITATION ARE FORECAST.

FORECASTER: ED O'LENIC

NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL 
PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES).

THE NEXT MONTHLY OUTLOOK...FOR JUNE 2008...WILL BE ISSUED ON THU MAY 15 2008

THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.

$$