PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
CLIMATE PREDICTION CENTER NCEP
NATIONAL WEATHER SERVICE  WASHINGTON D.C.
3 PM EDT THURSDAY DECEMBER 19 2002

30-DAY OUTLOOK DISCUSSION FOR JANUARY 2003
                                                                               .
THE EQUATORIAL PACIFIC SSTS AND ENSO-RELATED ATMOSPHERIC INDICES (SOI, 850-HPA 
ZONAL WIND INDEX) CONTINUE TO INDICATE MODERATE EL NINO CONDITIONS.  STATISTICAL 
AND NUMERICAL MODEL PREDICTIONS OF ENSO INDICATE THAT THE WARM EVENT WILL 
CONTINUE AT ITS CURRENT STRENGTH THROUGH AT LEAST THE MONTH OF JANUARY.  EL NINO 
PRODUCES A STRENGTHENED PACIFIC JET DISPLACED SOUTHWARD OF ITS NORMAL POSITION
...FAVORING STORM DEVELOPMENT WITH ENHANCED PRECIPITATION IN THE SOUTHERN HALF 
OF THE NATION AND GENERALLY DRY CONDITIONS IN THE NORTH.  A STRONGER THAN NORMAL 
MEAN ALEUTIAN LOW IS USUALLY OBSERVED IN EL NINO WINTERS... WHICH BRINGS 
ANOMALOUS WESTERLY FLOW INTO WESTERN CANADA AND DECREASES THE LIKELIHOOD OF 
ARCTIC AIR REACHING THE CONUS IN FAVOR OF RELATIVELY MILD MODIFIED PACIFIC AIR.
THIS FAVORS ABOVE NORMAL TEMPERATURES IN THE NORTHERN PORTION OF THE COUNTRY...
PARTICULARLY IN THE NORTHERN PLAINS.  RECENT TRENDS ALSO FAVOR ABOVE NORMAL 
TEMPERATURES THROUGHOUT MUCH OF THE NATION AS WELL.  THE SOUTHERN STORM TRACK 
FAVORS BELOW NORMAL TEMPERATURES ALONG THE GULF COAST AND IN THE SOUTHEASTERN 
U.S.  ALASKAN TEMPERATURES TENDS TO BE WARMER THAN NORMAL OVER MUCH OF THE 
STATE EXCEPT OVER THE ALEUTIANS WHERE BELOW NORMAL TEMPERATURES ARE FAVORED IN 
ASSOCIATION WITH THE TROUGH SUPPORTING THE ALEUTIAN LOW.  

THE TEMPERATURE FORECAST WAS BASED PRIMARILY ON WARM PHASE ENSO (EL NINO) 
COMPOSITES OF PAST MODERATE AND STRONG CASES DURING DJF.  THE ATMOSPHERIC 
CIRCULATION THIS FALL HAS CONSISTENTLY FAVORED THE NEGATIVE PHASE OF THE 
ARCTIC OSCILLATION (AO).  WHILE THE AO IS ONLY VERY WEAKLY PERSISTENT ON MONTH 
TO MONTH TIME SCALES... THE SUSTAINED NEGATIVE AO PHASE IN THE FALL VERY 
SLIGHTLY INCREASES ITS ODDS OF PERSISTING INTO JANUARY.  THE PROBABILITIES 
FROM ENSO COMPOSITES WERE ALTERED VERY SLIGHTLY TO REFLECT THE TEMPERATURE 
CONDITIONS DURING THE NEGATIVE AO PHASE IN ENSO WINTERS... WHICH BRINGS COOLER 
TEMPERATURES TO THE SOUTHEAST AND EAST COAST THAN FOR THE POSITIVE OR NEUTRAL
AO.  THE PROBABILITY ANOMALIES IN EASTERN ALASKA ARE SLIGHTLY HIGHER THAN WHAT 
ENSO COMPOSITES ALONE MAY INDICATE DUE TO THE CHANCES OF A PERSISTENT NEGATIVE
AO.  SSTS IN THE EASTERN PACIFIC WITHIN AND JUST SOUTH OF THE GULF OF ALASKA 
ARE MORE THAN 2 DEGREES C ABOVE NORMAL AND INCREASE THE CHANCES OF ABOVE NORMAL 
TEMPERATURES IN THE ALASKAN PANHANDLE AND THE PACIFIC NORTHWEST. 

THE PRECIPITATION FORECAST IS BASED PRIMARILY ON  ENSO COMPOSITES.  A CONSENSUS
OF 6 GCMS RUN AT NCEP AND OTHER CENTERS SHOW BASIC AGREEMENT WITH THE ENSO
COMPOSITES OVER MOST OF THE CONUS.  THE NUMERICAL MODELS SHOW BELOW MEDIAN 
PRECIPITATION FOR WESTERN ALASKA AND THE ALEUTIANS. 

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 JANUARY 16 2003.
  
NOTE - THE NEW 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE 
WITH THE MAY 17 2001 FORECAST RELEASE.

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