EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
231 PM EST TUE NOV 03 2009
 
VALID 12Z FRI NOV 06 2009 - 12Z TUE NOV 10 2009
 
A LOW AMPLITUDE LONGWAVE RIDGE OVER THE CENTRAL CONUS IS EXPECTED
TO ERODES IN RESPONSE TO APPROACH OF A VIGOROUS UPPER LOW FROM THE
GULF OF ALASKA TOWARD WESTERN NORTH AMERICA AT THE START OF THE
MEDIUM RANGE PERIOD. THE RESULT IS SHORT-LIVED ZONAL FLOW THAT
INFLUENCES THE MAJORITY OF THE CONUS THROUGH DAY 5 WHICH THEN
HELPS EJECT A COASTAL LOW FROM THE NORTHEAST. BEYOND DAY 5...THE
MAJORITY OF 00Z MODEL GUIDANCE TRENDED SLOWER/STRONGER WITH A
SHORTWAVE TROUGH AMPLIFYING OVER THE ROCKIES WHILE 12Z GUIDANCE
INCLUDING THE GFS/ECMWF/GEFS MEAN TRENDED FASTER/WEAKER...WITH
TIMING DIFFERENCES OF 24-36 HRS BY DAY 7. WHILE ACKNOWLEDGING THE
FASTER 12Z TREND...THE PREFERENCE REMAINS WITH THE SLOWER/DEEPER
SCENARIO UNTIL ADDITIONAL DAY 6/7 DETERMINISTIC AND ENSEMBLE
GUIDANCE BECOMES AVAILABLE AND DISPLAYS BETTER CLUSTERING.
THUS...LITTLE TO NO CHANGE WAS MADE TO THE PRELIMINARY UPDATE
ISSUED THIS MORNING...WHICH REFLECTS A BLEND OF THE 00Z GFS/ECMWF
DAYS 3/4...AND MAINLY THE 00Z ECMWF ENSEMBLE MEAN DAYS 6/7...WHICH
AGAIN IS SLOWER THAN THE NEW 12Z GEFS MEAN WITH THE TROUGH OVER
THE ROCKIES.  

PRECIPITATION WILL BE HEAVIEST ACROSS THE NORTHWEST IN THE MEDIUM
RANGE PERIOD DUE TO A SERIES OF SIGNIFICANT SHORTWAVE TROUGHS
INFLUENCING THE REGION WHILE A SECONDARY MAXIMA MAY DEVELOP
BENEATH THE AMPLIFYING ROCKIES SHORTWAVE TROUGH AND ALSO AHEAD OF
AN ASSOCIATED FRONTAL BOUNDARY ENTERING THE PLAINS.
MEANWHILE...MORE UNCERTAIN IS POTENTIAL SURFACE LOW DEVELOPMENT
ALONG A STALLED FRONTAL BOUNDARY IN THE BAY OF CAMPECHE AND IN
ASSOCIATION WITH A TROPICAL WAVE IN THE SOUTHWEST CARIBBEAN...WITH
MODEL CONSENSUS FOR CONDITIONS TO REMAIN FAVORABLE FOR ONE OR BOTH
REGIONS TO SUPPORT LOW DEVELOPMENT AT SOME POINT IN THE MEDIUM
RANGE PERIOD...WHICH MAY CONTRIBUTE TO ADDITIONAL AREAS OF
RAINFALL ALONG THE GULF COAST.
ELSEWHERE...THE MAIN IMPACT FROM THE ANTICIPATED SHORTWAVE PATTERN
IS UNUSUALLY STRONG WINDS DEVELOPING OVER MUCH OF THE CONUS
BEGINNING DAY 5...INCLUDING THE SOUTHEAST/PLAINS/SOUTHERN
CALIFORNIA.

JAMES