PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
CLIMATE PREDICTION CENTER NCEP
NATIONAL WEATHER SERVICE  WASHINGTON D.C.
3 PM EDT THURSDAY NOVEMBER 21 2002

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2002
                                                                               .
THE OVERALL SST AND ATMOSPHERIC INDICES (SOI, 850-HPA ZONAL WIND INDEX) 
INDICATE CONTINUING MODERATE STRENGTH EL NINO CONDITIONS.  THE STRONGEST 
ANOMALOUS CONVECTION REMAINS WELL ESTABLISHED NEAR AND JUST EAST OF THE DATE 
LINE.  AS THE SSTS IN THE TROPICAL PACIFIC CONTINUE TO WARM ...CONVECTION
WILL SHIFT FURTHER EAST TO THE EAST-CENTRAL AND THEN EASTERN PACIFIC.  AS THE
CONVECTION SHIFTS FURTHER EAST...THE EAST ASIAN JET STREAM WILL BUILD FURTHER
EAST ACROSS THE PACIFIC.  DECEMBER IS WHEN THE CONVECTION TYPICALLY STARTS TO
BUILD ACROSS THE PACIFIC DURING MODERATE WARM EPISODES. THE TRADITIONAL TOOLS 
- CCA AND OCN - STILL HAVE QUITE LOW SKILL DURING THIS MONTH AND ARE ALSO NOT
INDICATING MUCH ACROSS THE COUNTRY.

THE TEMPERATURE FORECAST WAS BASED PRIMARILY ON WARM PHASE ENSO (EL NINO) 
COMPOSITES OF PAST MODERATE AND STRONG CASES DURING NDJ.  NEITHER OCN OR CCA
HAVE ANY STATISTICALLY RELATIONSHIPS ACROSS THE CONUS.  ENSO COMPOSITES WOULD
FAVOR WARMTH ACROSS THE ENTIRE NORTHERN TIER OF THE COUNTRY.  HOWEVER BOTH 
MEDIUM AND LONG RANGE MODEL FORECASTS CONTINUE TO PREDICT THE NEGATIVE PHASE OF 
THE NAO DURING THE NEXT WEEKS.  BECAUSE OF THIS ...HAVE OPTED TO TRIM THE
FORECAST OF ABOVE NORMAL TEMPERATURES IN THE MIDWEST AND THE NORTHEAST...
RESORTING TO EC .  ACROSS THE SOUTH ...ENSO COMPOSITES DO NOT PROVIDE A STRONG 
SIGNAL ONE WAY OR THE OTHER.  NEGATIVE PHASE NAO WOULD IMPLY BELOW NORMAL 
TEMPERATURES IN THE SOUTHEAST ...BUT WE HAVE NO WAY OF KNOWING HOW LONG THE 
NEGATIVE PHASE OF THE NAO WILL LAST. THEREFORE FOR THE REST OF THE NATION HAVE 
OPTED FOR A FORECAST OF EC. 

NOTE -  AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILTIES) WILL HENCEFORTH BE LABELED EC (EQUAL CHANCES).  

THE PRECIPITATION FORECAST IS BASED PRIMARILY ON  ENSO COMPOSITES - AND IN 
AREAS WHERE OCN OR CCA REINFORCES IT THE PROBABILITIES AND AREAL COVERAGE 
WERE INCREASED.  THE TENDENCY FOR WETNESS FORECAST ACROSS PARTS OF THE SOUTH 
- MAINLY THROUGHOUT TEXAS - IS SUPPORTED BY BOTH EL NINO COMPOSITES AND RECENT 
TRENDS.  DRYNESS IN THE PACIFIC NORTHWEST IS INDICATED MAINLY BY ENSO 
COMPOSITES... WITH A SLIGHT TREND TOWARD DRYNESS HERE AS WELL.   FOR THE 
REMAINDER OF THE NATION - WHERE INDICATIONS ARE WEAK - EC IS FORECAST.

IN ALASKA THE BELOW NORMAL TEMPERATURE OVER THE WEST COMES FROM OCN AND THE 
WARMTH OVER THE SOUTHEAST AND PANHANDLE COMES FROM EXPECTED EL NINO FORCING 
PERHAPS ALREADY OCCURING AS SHOWN BY RECENT PATTERNS OF A TROUGH OVER THE 
CENTRAL PACIFIC AND A RIDGE NEAR OR JUST OFF THE WEST COAST OF THE U.S. AND 
BRITISH COLUMBIA - GIVING ONSHORE SOUTHERLY FLOW AND FORCING THE JET STREAM 
AND PREVAILING STORM TRACK TO THE NORTH.  TEMPERATURES ACROSS MUCH OF THIS
PART OF ALASKA HAVE AVERAGED WELL ABOVE NORMAL FOR THE PAST MONTH.

FORECASTER: M. HALPERT

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 - THE NEXT 0.5 MONTH LEAD-TIME MONTHLY OUTLOOK WILL BE ISSUED 
THURSDAY DECEMBER 19 2002.
  
NOTE - THE NEW 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE 
WITH THE MAY 17 2001 FORECAST RELEASE.

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