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.
$$