PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300PM EDT THURSDAY MAR 31 2011

30-DAY OUTLOOK DISCUSSION FOR APRIL 2011

LA NINA CONDITIONS ARE PRESENT ACROSS THE TROPICAL PACIFIC OCEAN. RECENTLY, SEA 
SURFACE TEMPERATURES (SSTS) NEAR THE EQUATOR IN THE EASTERN AND CENTRAL PACIFIC 
OCEAN HAVE BEEN AT LEAST 1 DEGREE C BELOW NORMAL FROM ABOUT 170W TO 130W.  SSTS 
FROM THE CENTRAL PACIFIC TO THE SOUTH AMERICAN COAST HAVE WARMED DURING THE 
LAST TWO WEEKS.  

THE SUBSURFACE OCEAN HEAT CONTENT IS BELOW NORMAL TO A DEPTH OF ABOUT 100 
METERS EAST OF THE DATELINE AND AT GREATER DEPTH EAST OF 140 W, WHILE ABOVE 
NORMAL SUB-SURFACE ANOMALIES IN THE WEST PACIFIC HAVE CONTINUED TO EXPAND 
EASTWARD AT DEPTH TO ABOUT 140 W BY LATE-MARCH.  

THE LARGE SCALE ATMOSPHERIC CIRCULATION OVER THE TROPICAL PACIFIC OCEAN IS 
CONSISTENT WITH LA NINA CONDITIONS. CONVECTION IS SLIGHTLY ENHANCED OVER PARTS 
OF THE MARITIME CONTINENT NEAR THE EQUATOR, AND IS ESPECIALLY ENHANCED NORTH OF 
THE EQUATOR, AND ALSO OVER AUSTRALIA, THE TIMOR SEA, AND THE INDIAN OCEAN 
NORTHWEST OF AUSTRALIA, AND SUPPRESSED OVER THE WESTERN AND CENTRAL EQUATORIAL 
PACIFIC OCEAN EAST OF 140E. LOW LEVEL EASTERLY TRADE WINDS ARE ENHANCED OVER 
THE WESTERN AND CENTRAL PACIFIC. WESTERLY WIND ANOMALIES AT UPPER LEVELS ARE 
ENHANCED OVER THE CENTRAL AND EAST-CENTRAL PACIFIC WITH ANOMALOUS 
OFF-EQUATORIAL CYCLONIC CIRCULATIONS IN THE SUBTROPICS OF BOTH HEMISPHERES.

THE APRIL 2011 TEMPERATURE AND PRECIPITATION OUTLOOKS WERE BASED ENTIRELY ON 
DYNAMICAL MODEL FORECASTS FROM THE GFS, OUT TO 8-14 DAYS, AND FROM THE CFS, 
VERSIONS 1 AND 2.  THE GFS WEEK 2 FORECAST INDICATES THE LIKELY CONTINUATION OF 
RELATIVELY FAST UPPER AIR FLOW OVER THE CONTIGUOUS U.S., WITH A MODEST UPPER 
AIR TROUGH IN THE SOUTHWEST, AND A WEAK UPPER AIR RIDGE OVER THE GULF COAST AND 
THE SOUTHEAST.  THIS PATTERN IS CONSISTENT WITH WARM TEMPERATURES OVER THE 
SOUTH-CENTRAL U.S. AND RELATIVELY COOL TEMPERATURES ALONG THE WEST COAST, AND 
ALONG THE NORTHERN TIER OF STATES, THROUGH NEW ENGLAND.  THE GFS IMPLIES DRY 
CONDITIONS FROM SOUTHERN CALIFORNIA THROUGH THE SOUTHERN ROCKIES, THE SOUTHERN 
GREAT PLAINS, ALONG THE IMMEDIATE GULF COAST AND FLORIDA.  CFS 1-MONTH 
FORECASTS FOR APRIL ARE CONSISTENT WITH THOSE OF THE GFS, BUT FEATURE WARM DRY 
CONDITIONS IN CALIFORNIA, TEXAS, ALONG THE IMMEDIATE GULF COAST, AND FOR THE 
FLORIDA PENINSULA.  CFS MODELS PREDICT UNUSUALLY COOL, WET CONDITIONS ACROSS 
THE NORTHERN CONTIGUOUS U.S., AND IN THE TENNESSEE AND OHIO VALLEY.  THIS 
PATTERN IS CONSISTENT WITH LA NINA, WHICH IS CURRENTLY STRONGLY REFLECTED IN 
THE ATMOSPHERE OVER THE TROPICS AND SUBTROPICS.  THESE CONSIDERATIONS HAVE BEEN 
TEMPERED AGAINST A KNOWN TENDENCY FOR ENSO IMPACTS TO WEAKEN DURING THE 
APPROACH OF, AND DURING, THE WARM SEASON.

THE TEMPERATURE OUTLOOK FOR APRIL 2011 INDICATES INCREASED CHANCES OF BELOW 
AVERAGE MEAN TEMPERATURES FOR CENTRAL AND NORTHERN CALIFORNIA, THE PACIFIC 
NORTHWEST, AND ACROSS THE NORTHERN ROCKIES TO THE NORTHERN GREAT PLAINS, THE 
GREAT LAKES, THE OHIO VALLEY, THE MIDDLE ATLANTIC REGION, AND THE NORTHEAST. 
THERE ARE ENHANCED ODDS OF BELOW NORMAL MEAN TEMPERATURES ALSO OVER SOUTHERN 
ALASKA.  ABOVE NORMAL TEMPERATURES ARE LIKELY FOR SECTIONS OF NORTHERN ALASKA. 
INCREASED CHANCES FOR ABOVE NORMAL TEMPERATURES ARE PREDICTED FROM THE 
SOUTHWEST THROUGH THE SOUTHERN GREAT PLAINS AND LOUISIANA.

THE PRECIPITATION OUTLOOK FOR APRIL 2011 INDICATES INCREASED CHANCES OF ABOVE 
MEDIAN PRECIPITATION IN CENTRAL AND NORTHERN SECTIONS OF ALASKA, NORTHERN 
CALIFORNIA, THE PACIFIC NORTHWEST, THE NORTHERN ROCKIES, THE NORTHERN GREAT 
PLAINS, THE GREAT LAKES SOUTHWARD TO THE OHIO AND TENNESSEE VALLEYS, THE MIDDLE 
ATLANTIC STATES, AND SOUTHERN NEW ENGLAND. BELOW MEDIAN PRECIPITATION IS 
PREDICTED TO BE MOST LIKELY FROM SOUTHERN CALIFORNIA THROUGH THE SOUTHERN 
ROCKIES, THE SOUTHERN GREAT PLAINS, AND ALONG THE IMMEDIATE GULF COAST AND 
FLORIDA. THE SOUTHERN COAST OF ALASKA AND THE ALASKAN PANHANDLE ARE ALSO 
INDICATED TO HAVE INCREASED CHANCES OF BELOW MEDIAN PRECIPITATION.  

WHERE THERE ARE NO CLEAR CLIMATE SIGNALS DURING THE FORECAST PERIOD, EQUAL 
CHANCES (EC) OF BELOW, NEAR, AND ABOVE NORMAL FOR TEMPERATURE AND BELOW, NEAR, 
AND ABOVE MEDIAN FOR PRECIPITATION ARE INDICATED.


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 MAY ... WILL BE ISSUED ON THU APR 21 2011


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

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