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FXUS07 KWBC 151421
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EST THU NOV 15 2007
30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2007
LA NINA CONDITIONS STRENGTHENED DURING OCTOBER 2007, AS NEGATIVE SST ANOMALIES
ALONG THE EQUATOR EXPANDED WESTWARD AND NOW EXTEND FROM 160E TO THE SOUTH
AMERICAN COAST. THE LATEST WEEKLY ANALYSIS OF EQUATORIAL PACIFIC SSTS SHOWS THE
LARGEST DEPARTURES FROM NORMAL OF AROUND -3 DEGREES C BETWEEN 90 AND 120W AND
DEPARTURES MORE THAN 1 DEGREE C BELOW NORMAL FROM AROUND THE DATELINE TO THE
SOUTH AMERICAN COAST. THE UPPER-OCEAN HEAT CONTENT (AVERAGE TEMPERATURES IN
THE UPPER 300 M OF THE OCEAN) IN THE CENTRAL AND EAST-CENTRAL EQUATORIAL
PACIFIC REMAINED WELL BELOW AVERAGE IN EARLY NOVEMBER. THIS INDICATES A
SUBSTANTIAL VOLUME OF WATER WITH BELOW NORMAL TEMPERATURES IN THE UPPER LEVELS
OF THE OCEAN AND SUGGESTS THAT THE SSTS WILL REMAIN BELOW NORMAL THROUGH THE
END OF THE YEAR. CONSISTENT WITH THESE CONDITIONS, THE LOW-LEVEL EASTERLY
WINDS WERE STRONGER THAN AVERAGE ACROSS THE CENTRAL EQUATORIAL PACIFIC,
CONVECTION REMAINED SUPPRESSED THROUGHOUT THE CENTRAL AND EASTERN EQUATORIAL
PACIFIC, AND SLIGHTLY ENHANCED CONVECTION COVERED PARTS OF INDONESIA AND THE
FAR WESTERN PACIFIC. COLLECTIVELY, THESE OCEANIC AND ATMOSPHERIC CONDITIONS
REFLECT MODERATE LA NINA CONDITIONS.
LA NINA CONDITIONS ARE EXPECTED TO HAVE CONSIDERABLE IMPACT ON U.S.
TEMPERATURE AND PRECIPITATION IN DECEMBER. LA NINA IS ASSOCIATED WITH ABOVE
NORMAL TEMPERATURES IN THE DESERT SOUTHWEST, THE SOUTHERN GREAT PLAINS, TEXAS,
AND MUCH OF THE EASTERN CONUS. TRENDS TOWARD ABOVE NORMAL TEMPERATURES ENHANCE
THE INFLUENCE OF LA NINA IN THESE REGIONS AND EXTEND THE AREA OF EXPECTED ABOVE
NORMAL TEMPERATURES TO INCLUDE THE GREAT LAKES AND UPPER MISSISSIPPI VALLEY.
LA NINA IS ASSOCIATED WITH BELOW NORMAL TEMPERATURES IN THE NORTHERN ROCKIES,
PACIFIC NORTHWEST AND MUCH OF ALASKA, SO TEMPERATURES IN THESE REGIONS ARE
EXPECTED TO BE BELOW THE AVERAGES IN RECENT YEARS, HOWEVER WHEN RECENT WARMING
TRENDS ARE TAKEN INTO ACCOUNT TEMPERATURES ARE EXPECTED TO REFLECT THE
CLIMATOLOGICAL FREQUENCIES FROM THE 1971-2000 BASE PERIOD.
PRECIPITATION TENDS TO BE LIGHT OVER MUCH OF THE SOUTHERN PART OF THE
COUNTRY IN LA NINA WINTERS, SO THE CHANCES OF BELOW MEDIAN PRECIPITATION IN
DECEMBER IS ENHANCED IN THE SOUTHERN PART OF THE CONUS FROM SOUTHERN CALIFORNIA
THROUGH TO THE EAST COAST, EXTENDING NORTHWARD ALONG THE EASTERN SEABOARD TO
SOUTHERN NEW ENGLAND. THIS SIGNAL IS SUPPORTED BY A BROAD RANGE OF TOOLS
INCLUDING DYNAMIC MODEL FORECASTS FROM THE CFS AND IRI MULTI-MODEL ENSEMBLE.
THE CFS SUGGESTS ABOVE MEDIAN PRECIPITATION AMOUNTS FOR THE PACIFIC NORTHWEST
AND NORTHERN ROCKIES, WITH ADDITIONAL SUPPORT FROM COMPOSITES.. ESPECIALLY NEAR
THE NORTHERN ROCKIES. THE CFS AND IRI MODEL PREDICT ABOVE MEDIAN PRECIPITATION
AMOUNTS FOR SOUTHWESTERN ALASKA, WITH SOME ADDITIONAL SUPPORT FROM SMLR.
FORECASTER: DAVID UNGER
NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES).
AN UPDATED MONTHLY OUTLOOK... FOR DEC WILL BE ISSUED ON FRI NOVEMBER 30 2007
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.
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