PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
3 PM EDT THURSDAY JANUARY 16 2003

30-DAY OUTLOOK DISCUSSION FOR FEBRUARY 2003
                                                                               .
THE EQUATORIAL PACIFIC SSTS AND ENSO-RELATED ATMOSPHERIC INDICES (SOI, 850-HPA 
ZONAL WIND INDEX) INDICATE MODERATE EL NINO CONDITIONS CONTINUING IN THE FIRST
HALF OF JANUARY.  STATISTICAL AND NUMERICAL MODEL SST PREDICTIONS INDICATE 
THAT CENTRAL EQUATORIAL PACIFIC SSTS WILL REMAIN MORE THAN 1 DEGREE C 
ABOVE NORMAL THROUGH THE END OF FEBRUARY.  SSTS ALONG THE EQUATOR FROM ABOUT 
120W TO THE SOUTH AMERICAN COAST ARE ONLY SLIGHTLY HIGHER THAN NORMAL... WHICH 
MAY BE LIMITING THE ATMOSPHERIC RESPONSE TO EL NINO.  THE EL NINO TELE-
CONNECTIONS DEPEND ON ABNORMALLY STRONG CONVECTION ALONG THE EQUATOR IN THE 
EAST CENTRAL PACIFIC OCEAN IN RESPONSE TO the WARM SSTS .  WITH EASTERN 
EQUATORIAL PACIFIC SSTS CURRENTLY COOLER THAN IN A TYPICAL WARM EVENT... THE 
EASTERN EXTENT OF CONVECTION IS LIMITED AND THE ASSOCIATED EXTRA-TROPICAL 
RESPONSE TO EL NINO MAY BE WEAKER THAN EXPECTED.  HOWEVER... OCEAN TEMPERATURES 
JUST BELOW THE SURFACE ARE WELL ABOVE NORMAL THROUGHOUT THE EASTERN PACIFIC 
MAKING IT LIKELY THAT SST ANOMALIES THERE WILL MAINTAIN THEIR CURRENT STRENGTH - 
AND PERHAPS EVEN INCREASE.   ANOTHER FACTOR THAT HAS LIMITED THE TYPICAL 
ATMOSPHERIC RESPONSE TO EL NINO SO FAR THIS WINTER IS THE PERSISTENT BLOCKING AT 
HIGH LATITUDES OBSERVED IN THE PAST FEW MONTHS.  THE ARCTIC OSCILLATION AND NAO 
HAVE FAVORED THEIR NEGATIVE PHASES - WITH THE PNA IN ITS POSITIVE PHASE SINCE 
MID-OCTOBER... BRINGING COOLER THAN NORMAL TEMPERATURES TO THE EASTERN HALF OF 
THE U.S.  THESE HIGH LATITUDE BLOCKING PATTERNS ARE UNPREDICTABLE BEYOND ABOUT 
TWO WEEKS EXCEPT FOR SLIGHT AMOUNT OF PERSISTENCE AT THIS TIME OF YEAR.  THE 
CIRCULATION PATTERNS ASSOCIATED WITH EL NINO... ON THE OTHER HAND... ARE FORCED 
BY SST ANOMALIES AND THUS ARE PREDICTED TO OCCUR WITH GREATER FREQUENCY THIS 
YEAR WHEN COMPARED TO A NORMAL WINTER. THE MONTHLY FORECAST REFLECTS THE 
PREDICTABLE COMPONENT OF THE ATMOSPHERIC CIRCULATION ASSOCIATED WITH EL NINO... 
BUT WITH LOWER PROBABILITIES ANOMALIES THAN WOULD OTHERWISE BE EXPECTED BECAUSE 
OF WEAK SST ANOMALIES IN THE EASTERN EQUATORIAL PACIFIC AND THE PERSISTENT 
BLOCKING THAT HAS BEEN OBSERVED RECENTLY.    

THE TEMPERATURE FORECAST WAS BASED PRIMARILY ON TREND ADJUSTED WARM PHASE ENSO 
(EL NINO) COMPOSITES OF PAST MODERATE AND STRONG CASES DURING JFM AND FMA.  THE 
PROBABILITIES FROM ENSO COMPOSITES WERE ALTERED TO REFLECT THE POSSIBILITY OF 
THE CONTINUED PERSISTENCE OF THE NEGATIVE AO PHASE.  PROBABILITY ANOMALIES FOR
ABOVE NORMAL TEMPERATURES TO THE EAST OF THE ROCKY MOUNTAINS ARE SOMEWHAT LOWER 
THAN NORMALLY EXPECTED IN MODERATE WARM EVENTS.

THE PRECIPITATION FORECAST IS BASED PRIMARILY ON ENSO COMPOSITES FROM JFM
AND FMA... AND THE FMA PREDICTIONS FROM A MULTI-MODEL ENSEMBLE OF GCMS RUN 
AT NCEP AND OTHER CENTERS.  THE MODELS AGREED WELL WITH ENSO COMPOSITES 
EXCEPT OVER THE NORTHEASTERN U.S... WHERE THE SEASONAL FORECAST FROM THE GCM
APPEAR MUCH DRIER THAN ENSO COMPOSITES SUGGEST.  THE SEASONAL ENSO COMPOSITES
INDICATING ABOVE MEDIAN PRECIPITATION IN THE CENTRAL ROCKIES WERE REVISED 
TO EQUAL CHANCES BECAUSE ENSO-RELATED ANOMALIES APPEAR IN THE SPRING AND ARE 
LESS RELIABLE IN LATE WINTER.
   

FORECASTER: D. UNGER

NOTE - THIS CLIMATE OUTLOOK IS INTENDED FOR USE ONLY PRIOR TO THE START OF THE 
VALID PERIOD.  WITHIN THE VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM RANGE 
FORECASTS SHOULD BE CONSULTED.

NOTE -  AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILTIES) WILL HENCEFORTH BE LABELED EC (EQUAL CHANCES).  
  
NOTE - THE NEXT 0.5 MONTH LEAD-TIME MONTHLY OUTLOOK WILL BE ISSUED 
THURSDAY FEBRUARY 20 2003.
  
NOTE - THE NEW 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE 
WITH THE MAY 17 2001 FORECAST RELEASE.

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