882
FXUS07 KWBC 311919
PMD30D
PROGNOSTIC DISCUSSION FOR REVISED MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT SAT MAY 31 2008
30-DAY OUTLOOK DISCUSSION FOR JUNE 2008
SEA SURFACE TEMPERATURES (SST) ALONG THE EQUATOR IN THE EAST CENTRAL PACIFIC OCEAN
REMAIN BELOW NORMAL BUT THE MAGNITUDE OF THE ANOMALIES HAVE SLOWLY DIMINISHED IN
THE LAST TWO WEEKS. SST ANOMALIES IN THE NINO 3.4 REGION (BETWEEN 5 N AND 5 S,
AND 170W AND 120W) WERE ABOUT .8 DEGREES C BELOW NORMAL IN MID-MAY, AND NOW ARE
AROUND -.4 C. THE ATMOSPHERIC CIRCULATION THROUGHOUT THE TROPICAL PACIFIC OCEAN
CONTINUES TO REFLECT LA NINA CONDITIONS, WITH ENHANCED LOW LEVEL EASTERLIES ALONG
THE EQUATOR, AND SUPPRESSED CONVECTION IN THE CENTRAL EQUATORIAL PACIFIC. MOST
NUMERICAL AND STATISTICAL MODELS CONTINUE TO WEAKEN SST ANOMALIES IN THE NINO 3.4
REGION OVER THE NEXT FEW MONTHS. THE LATEST CFS MODEL FORECAST SHOWS RAPID
WEAKENING OF THE SST ANOMALIES... HOWEVER THE MJO IS CURRENTLY ACTIVE AND MAY
INFLUENCE THE CFS FORECASTS AS WELL AS PRODUCE SUBSTANTIAL SHORT TERM FLUCTUATIONS
IN WEEKLY MEAN SSTS THE NEAR FUTURE. THE MONTHLY MEAN SST ANOMALY IN THE NINO 3.4
REGION IS EXPECTED TO REMAIN NEGATIVE, BUT BE SMALLER THAN IN MAY. THUS LA NINA
IS EXPECTED TO HAVE NEGLIGIBLE IMPACT ON U.S. TEMPERATURES AND PRECIPITATION IN
JUNE.
SSTS ALONG THE WESTERN COAST OF NORTH AMERICA ARE BELOW NORMAL AND ARE EXPECTED TO
FAVOR BELOW NORMAL AIR TEMPERATURES ALONG IMMEDIATE COASTAL AREAS FROM THE SOUTH
COAST OF ALASKA TO SOUTHERN CALIFORNIA. THE CFS, CCA, AND OCN INDICATE ABOVE
NORMAL TEMPERATURES IN THE SOUTHWESTERN U.S. AND THE GREAT BASIN. THE CFS
CONTINUES TO SUGGEST ELEVATED CHANCES OF A LONG WAVE UPPER LEVEL RIDGE JUST OFF
THE WEST COAST WITH A TROUGH IN THE EAST AS IT DID IN ITS MID-MAY RUNS... HOWEVER
SHORT TERM FORECASTS SUGGEST THAT THE MEAN TROUGH WILL BE FARTHER WEST THAN THE
CFS INDICATES... INCREASING THE CHANCES FOR BELOW NORMAL MONTHLY MEAN TEMPERATURES
FROM THE THE PACIFIC NORTHWEST TO THE NORTHERN GREAT PLAINS... AND SUBSTANTIALLY
DECREASING THE CHANCES OF ABOVE NORMAL TEMPERATURES IN THE GREAT BASIN FROM THE
FORECAST RELEASED IN MID-MAY. ABOVE NORMAL TEMPERATURES ARE EXPECTED FOR PORTIONS
OF THE SOUTHERN GREAT BASIN AND SOUTHWESTERN STATES DUE PRIMARILY TO TRENDS. MEAN
UPPER LEVEL HEIGHTS OVER THE EASTERN U.S. ARE EXPECTED TO BE ABOVE NORMAL IN THE
FIRST HALF OF JUNE... AND THIS WILL INCREASE THE ODDS OF THE MONTHLY MEAN
TEMPERATURES FINISHING THE MONTH IN THE ABOVE NORMAL CATEGORY IN NEW ENGLAND AND
PARTS OF THE MID-ATLANTIC STATES. SOIL MOISTURE IS MUCH ABOVE NORMAL FROM THE
MIDDLE-MISSISSIPPI VALLEY TO THE OHIO RIVER VALLEY, WHICH FAVORS BELOW NORMAL
TEMPERATURES DUE TO INCREASED EVAPORATIVE COOLING... HOWEVER THE AREA OF
ANTICIPATED BELOW NORMAL TEMPERATURES WAS SHIFTED NORTHWESTWARD FROM THE OUTLOOK
RELEASED IN MID-MAY DUE TO SHORT TERM FORECASTS OF A WARM START TO THE MONTH IN
PARTS OF THE EASTERN CONUS.
LOCAL SOIL MOISTURE CONDITIONS ARE ASSOCIATED WITH INCREASED CHANCES FOR ABOVE
MEDIAN RAINFALL FOR THE MIDDLE MISSISSIPPI AND PORTIONS OF THE OHIO RIVER VALLEYS.
THIS IS SUPPORTED BY SHORT TERM FORECASTS OF ABOVE MEDIAN PRECIPITATION IN THE
AREA. DRY CONDITIONS ARE FORECAST IN PARTS OF THE WEST BY THE CFS MODEL AND THE
CAS SOIL MOISTURE ANALOG TOOL. HOWEVER WITH A MEAN UPPER LEVEL TROUGH EXPECTED
OVER THE NORTHERN ROCKIES EARLY IN THE MONTH, PRECIPITATION CHANCES ARE EXPECTED
TO BE HIGH ENOUGH TO COUNTERACT DRY SIGNALS FROM THESE MODELS OVER THE NORTHERN
ROCKIES AND THE PACIFIC NORTHWEST, SO THE AREA OF EXPECTED DRY CONDITIONS WAS
TRIMMED BACK ON THIS OUTLOOK FROM THE EARLIER MONTHLY OUTLOOK. SHORT TERM
FORECAST SHOW INCREASED CHANCES OF SIGNIFICANT PRECIPITATION FROM THE NORTHERN
PLAINS TO THE UPPER MISSISSIPPI VALLEY... SO THE REGION OF EXPECTED ABOVE MEDIAN
RAINFALL WAS EXTENDED NORTHWESTWARD FROM THE AREA INDICATED IN THE JUNE OUTLOOK
ISSUED TWO WEEKS AGO.
FORECASTER: DAVID UNGER
NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES).
THE NEXT MONTHLY OUTLOOK...FOR JULY 2008...WILL BE ISSUED ON THU JUN 19 2008
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.
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