PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT WED OCT 31 2007

30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2007

LA NINA CONDITIONS STRENGTHENED DURING OCTOBER 2007, AS NEGATIVE SST ANOMALIES 
ALONG THE EQUATOR EXPANDED WESTWARD AND NOW EXTEND FROM 160E TO THE SOUTH 
AMERICAN COAST. THE LATEST WEEKLY ANALYSIS SHOWS THE LARGEST SST DEPARTURES 
(-2C TO -3C) BETWEEN 140W AND THE COAST, WITH DEPARTURES OF -0.5C TO -1C 
CENTERED NEAR THE DATE LINE. THE MAGNITUDE OF THE NEGATIVE SST ANOMALIES 
INCREASED IN ALL OF THE NINO REGIONS, WITH THE NINO-3.4 INDEX DROPPING TO -1.4C 
AND THE NINO-4 INDEX DROPPING TO -0.6C BY THE END OF THE MONTH. THE UPPER-OCEAN 
HEAT CONTENT (AVERAGE TEMPERATURES IN THE UPPER 300 M OF THE OCEAN) IN THE 
CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC REMAINED BELOW AVERAGE DURING 
SEPTEMBER, WITH TEMPERATURES RANGING FROM 3C TO 6C BELOW AVERAGE AT THERMOCLINE 
DEPTH. CONSISTENT WITH THESE CONDITIONS, THE LOW-LEVEL EASTERLY WINDS AND 
UPPER-LEVEL WESTERLY WINDS REMAINED STRONGER THAN AVERAGE ACROSS THE CENTRAL 
EQUATORIAL PACIFIC, CONVECTION REMAINED SUPPRESSED THROUGHOUT THE CENTRAL AND 
EASTERN EQUATORIAL PACIFIC, AND ENHANCED CONVECTION AGAIN COVERED PARTS OF 
INDONESIA AND THE FAR WESTERN PACIFIC. COLLECTIVELY, THESE OCEANIC AND 
ATMOSPHERIC CONDITIONS REFLECT A STRENGTHENING LA NINA.

GFS AND OTHER DYNAMICAL MODEL FORECASTS FOR WEEK 2 HAVE BEEN USED WITH LARGE 
WEIGHT IN THIS ZERO LEAD-TIME FORECAST.  LA NINA COMPOSITES WERE ALSO 
CONSULTED.  THE WEEK 2 FORECASTS INDICATE A 500 HPA HEIGHT ANOMALY PATTERN 
HAVING A RIDGE IN WESTERN NORTH AMERICA AND A TROUGH IN THE EAST.  THIS PATTERN 
FOSTERS WARM, DRY CONDITIONS IN THE WEST, ROCKIES, GREAT PLAINS, GREAT LAKES 
AND DOWN THE MISSISSIPPI VALLEY, AND COLD TEMPERATURES IN THE GREAT LAKES AND 
NORTHERN GREAT PLAINS, WARM TEMPERATURES OVER MUCH OF ALASKA, AND WET 
CONDITIONS OVER SOUTHERN SECTIONS OF ALASKA.  HOWEVER, BECAUSE THE PREDICTED 
UPPER AIR HEIGHT PATTERN IS NEARLY OPPOSITE OF WHAT TENDS TO OCCUR, ON AVERAGE, 
DURING LA NINA, IT IS MORE LIKELY THAN USUAL THAT THE PREDICTED PATTERN IS 
TRANSIENT.  THIS INCREASES THE RISK OF A CHANGE IN THE PATTERN AFTER WEEK 2.  
THEREFORE, THE FORECAST DOES NOT CALL FOR BELOW NORMAL TEMPERATURES IN THE 
CENTRAL AND EASTERN CONUS, AS INDICATED IN THE WEEK 2 FORECAST.  THE WARM 
FORECAST FOR ALASKA RESULTS FROM A STRONG CONSENSUS AMONG MODELS.

THE FORECAST CALLS FOR ABOVE NORMAL TEMPERATURES IN THE WEST AND ALASKA, 
BELOW-MEDIAN PRECIPITATION IN MUCH OF THE WEST, THE ROCKIES, THE GREAT PLAINS, 
THE GREAT LAKES AND DOWN THE MISSISSIPPI VALLEY, AND ABOVE-MEDIAN PRECIPITATION 
IN SOUTHERN SECTIONS OF ALASKA EAST OF 160W.


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 DECEMBER 2007...WILL BE ISSUED ON THU NOV 15 2007

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

$$