891
FXUS02 KWBC 021907
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
206 PM EST MON NOV 02 2009
VALID 12Z THU NOV 05 2009 - 12Z MON NOV 09 2009
ASIDE FROM A MODEST CYCLONE DEVELOPING OFF THE NORTHEAST COAST AND
AN EVEN MORE POWERFUL CYCLONE IMPACTING THE GULF OF ALASKA DAYS
3/4...THE MODELS AGREE THAT ZONAL TO WEAKLY AMPLIFIED LONGWAVE
FLOW WILL IMPACT THE CONUS DAYS 3-5 BEFORE AMPLIFYING THEREAFTER.
12Z GUIDANCE DISPLAYS SIMILAR DETERMINISTIC AND ENSEMBLE SPREAD
REGARDING THE NORTHEAST COASTAL LOW...WHICH HAS BEEN AND CONTINUES
TO SHOW ABOVE AVERAGE UNCERTAINTY...WITH THE UNCERTAINTY INVOLVING
HOW THE VARIOUS MODELS HANDLE THE POTENTIAL PHASING OF 2 SHORTWAVE
TROUGHS AND WHEN/WHERE IT MAY OCCUR. THE PHASING OF THE TWO
SYSTEMS APPEARS REASONABLE AND IS AGREED UPON BY THE MODELS...WITH
THE FINAL MANUAL PROGS REPRESENTING A BLEND OF THE FASTER 00Z
ECMWF ENSEMBLE MEAN/SLOWER 12Z GEFS MEAN.
OTHERWISE...THE REMAINING UNCERTAINTY INVOLVES POTENTIAL TROPICAL
AND/OR HYBRID SURFACE LOW DEVELOPMENT NEAR THE YUCATAN PENINSULA
DAYS 6/7...WITH THE 00Z CANADIAN STILL THE STRONGEST AND FASTEST
WITH LIFTING IT NORTHWARD TOWARD THE CENTRAL GULF COAST. BELIEVE
THIS SCENARIO REPRESENTS A WORST CASE AND LOW PROBABILITY SCENARIO
GIVEN ITS LONG TIME RANGE AND LACK OF AGREEMENT FROM OTHER
GUIDANCE. RATHER...HAVE FOLLOWED A CONSENSUS OF THE MAJORITY OF
DETERMINISTIC/ENSEMBLE GUIDANCE...WHICH WHEN AVERAGED...PRODUCES A
WEAK MORE SOUTHWARD LOW THAT DRIFTS NORTHWARD INTO THE BAY OF
CAMPECHE BY DAY 7.
HOWEVER...OF ALL THE SYSTEMS TO INFLUENCE THE CONUS IN THE MEDIUM
RANGE PERIOD...PERHAPS THE MOST SIGNIFICANT WILL BE THE UNUSUALLY
DEEP CYCLONE THAT REACHES THE GULF OF ALASKA DAY 3 WITH A MINIMUM
CENTRAL PRESSURE NEAR 940 MB WHICH THEN IMPACTS THE PACIFIC
NORTHWEST WITH HEAVY RAIN AND MOUNTAIN SNOWS DAYS 3/4...WITH
ADDITIONAL ONSHORE FLOW AND WEAKER SHORTWAVE TROUGHS CONTINUING
THE IMPACT THE NORTHWEST THROUGH ABOUT DAY 5. MEANWHILE...THE
NORTHEAST COAST LOW MAY BE TOO FAR OFFSHORE TO PROVIDE MUCH MORE
THAN JUST A CHANCE OF PRECIPITATION ALONG THE IMMEDIATE COAST
ESPECIALLY NEW ENGLAND...WITH ONLY A SLIGHT WESTWARD ADJUSTMENT TO
ITS TRACK SUPPORTING CONSIDERABLY HIGHER AMOUNTS. ABOVE AVERAGE
MODEL SPREAD REGARDING THE PHASING PROCESS MENTIONED ABOVE
SUPPORTS BELOW AVERAGE CONFIDENCE IN THIS PARTICULAR SYSTEM. THE
TROPICAL OR HYBRID LOW FORMING NEAR THE YUCATAN PENINSULA DAYS 6/7
HAS THE POTENTIAL TO BRING HEAVY PRECIPITATION TO PARTS OF THE
GULF COAST/SOUTHEAST/EAST COAST. HOWEVER...ITS IMPACTS APPEAR TO
OCCUR MOSTLY AFTER DAY 7. HOWEVER...STRONG ONSHORE FLOW AND
ACCOMPANYING BETTER THAN AVERAGE CHANCES OF RAIN ARE EXPECTED TO
DEVELOP ALONG THE EASTERN FLORIDA COAST DUE TO THE INCREASING
PRESSURE GRADIENT BETWEEN THE SURFACE HIGH TO THE NORTH AND THE
LOW NEAR THE YUCATAN PENINSULA. ELSEWHERE...A WARMING TREND WITH
MAINLY DRY CONDITIONS WILL DEVELOP FROM THE PLAINS EASTWARD
STARTING DAY 4.
JAMES
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