506
FXUS02 KWBC 301902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
259 PM EDT FRI MAY 30 2008
VALID 12Z MON JUN 02 2008 - 12Z FRI JUN 06 2008
TELECONNECTIONS WITH A NEGATIVE ANOMALY OVER NUNAVUT AND A
POSITIVE ANOMALY MOVING ACROSS THE EASTERN PACIFIC FAVOR TROUGHING
NEAR THE WEST COAST INITIALLY BEFORE THE TROUGH PROGRESSES TOWARDS
THE GREAT BASIN EAST OF THE MOBILE PACIFIC POSITIVE ANOMALY/BROAD
RIDGE. A BUILDING POSITIVE ANOMALY OVER GREENLAND SHOULD ALLOW
FOR A PROGRESSIVE CLOSED CYCLONE UNDER ITS BASE NEAR THE 50TH
PARALLEL IN THE ATLANTIC. THE MODELS AGREE ON THESE IDEAS.
THE BIGGEST DETAIL DIFFERENCE IN THE GUIDANCE IS WHETHER OR NOT A
CLOSED CYCLONE WILL MOVE ACROSS THE NORTHERN PLAINS INTO THE GREAT
LAKES MID NEXT WEEK. WHILE THIS FEATURE IS SEEN ON THE 06Z AND
12Z GFS/00Z AND 12Z CANADIAN SOLUTIONS...IT IS NOT SEEN ON THE
OTHER OPERATIONAL GUIDANCE. THE BIGGEST PROBLEM WITH THIS SYSTEM
IS THAT IT BULLDOZES THE TOP OF THE MEAN RIDGE BETWEEN THE WESTERN
TROUGH AND TROUGHING IN THE WESTERN ATLANTIC...WOULD THINK IT
WOULD BE A MORE OPEN AND MORE NORTHERLY PROGRESSING UPPER TROUGH
RATHER THAN A CLOSED CYCLONE. THE GFS HAS SHOWN VIRTUALLY NO
CONSISTENCY WITH THIS SYSTEM...SIGNIFICANTLY TRENDING TOWARDS A
SLOWER SOLUTION WITH THE SURFACE WAVE SINCE ITS 29/00Z
RUN...NORMALLY A SYMPTOM OF GRIDSCALE FEEDBACK. THE NCEP ENSEMBLE
MEMBERS ARE HAVING PROBLEMS PICKING UP THIS SYSTEM DUE TO ITS
RELATIVELY SMALL SIZE...WHILE A HANDFUL OF ECMWF MEMBERS DO SHOW
THE SYSTEM...BUT MOVE IT AT A FASTER CLIP. NOT ENOUGH ENSEMBLE
MEMBERS HAVE IT TO MAKE A DENT IN THE 00Z ECMWF ENSEMBLE MEAN
MINOR RIDGE AXIS ACROSS THE MIDWEST/MISSISSIPPI VALLEY...SO PLAN
TO DOWNPLAY THIS SYSTEM USING A 00Z ECMWF/00Z NCEP ENSEMBLE MEAN
COMPROMISE.
ACROSS THE ROCKIES LATE IN THE PERIOD...THE 00Z ECMWF IS ON THE
DEEP FRINGE OF THE GUIDANCE WITH THE TROUGHING DEVELOPING OVER
COLORADO NEXT THURSDAY MORNING. THE INCREASED RIDGING IN THE
EASTERN PACIFIC ALLOWS FOR AMPLIFICATION OF THE TROUGH AS IT MOVES
THROUGH THE ROCKIES...BUT WOULD PREFER NOT TO BE AS DEEP AS THE
00Z ECMWF WITH THIS SYSTEM. THE 12Z ECMWF IS NOT ANY WEAKER WITH
THE TROUGHING THAN ITS 00Z RUN. WITH ALL THAT SAID...WILL FAVOR
THE 00Z ECMWF EARLY ON BEFORE BLENDING IN THE 00Z NCEP ENSEMBLE
MEAN FROM TUESDAY NIGHT ONWARD TO ACCOUNT FOR UNCERTAINTY IN THE
DETAILS OF THE FORECAST.
IN THE TROPICS...THE REMNANTS OF ALMA SHOULD TRACK WESTWARD
NEAR/SOUTH OF THE 20TH PARALLEL BASED UPON THE EXPECTED DEEP LAYER
RIDGE ACROSS NORTHERN MEXICO AND THE WESTERN GULF OF MEXICO
COASTLINE. NO MATTER WHICH MODEL YOU PICK...UPPER TROUGHING IS
EXPECTED TO DEVELOP OVER THE GULF OF MEXICO IN THE WAKE OF
ALMA/ITS REMAINS...WHICH SHOULD LEAD TO A SLIGHTLY DELAYED ONSET
/BY 5 TO 6 DAYS/ OF THE RAINY SEASON ACROSS SOUTHERN FLORIDA.
ROTH
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