011
FXUS02 KWBC 171915
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
313 PM EDT THU JUL 17 2008
VALID 12Z SUN JUL 20 2008 - 12Z THU JUL 24 2008
PRELIMINARY UPDATE...
THE 00Z GFS WAS ONCE AGAIN AN OUTLIER AMONG ITS MODEL PEERS FROM
THAT CYCLE WITH SEVERAL KEY SYSTEMS ACROSS THE UNITED STATES...AND
AS SUCH...WAS NOT INCORPORATED INTO THE BLEND USED TO CREATE THE
UPDATED FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7. INSTEAD...USED
THE 00Z DETERMINISTIC ECMWF AT THE BEGINNING OF THE PERIOD...WITH
A GRADUAL TRANSITION TO AN EVEN SPLIT WITH THE EUROPEAN CENTRE
ENSEMBLE MEAN BY DAY 5. THE 00Z UKMET IN IN SYNC WITH THIS
BLEND...AND TO A LESSER EXTENT...THE GEM GLOBAL. THE 00Z GEFS
MEAN IS FAIRLY SUPPORTIVE AS WELL...ALTHOUGH SHOWS MORE AMPLITUDE
THAN THE PREFERRED CLUSTER WITH THE SOUTHERN END OF THE EASTERN
TROUGH SOUTH OF THE OHIO VALLEY. BELIEVE THAT WRAPPING ENERGY
AROUND THE BLOCK OVER EASTERN CANADA FITS BEST. AT LEAST THE 00Z
GFS BACKED OFF ITS AGGRESSIVE HANDLING OF THE TROUGH SPLITTING
ALONG THE WEST COAST.
A NEW TREND ON THE 00Z CYCLE IS TO TAKE THE SOUTHERN END OF AN OLD
SHEAR AXIS ALONG THE GEORGIA COAST AND DEVELOP IT INTO A DISTINCT
LOW PRESSURE AREA...WHICH THEN PARALLELS THE SOUTHEAST COAST AND
EVENTUALLY EJECTS INTO THE CANADIAN MARITIMES. THE DETERMINISTIC
ECMWF...GEM GLOBAL...AND UKMET ARE ALL SURPRISINGLY CLOSE WITH THE
MID LEVEL REFLECTION OF THIS SYSTEM EAST OF HATTERAS AT THE
BEGINNING OF DAY 6. THE 00Z GFS WAS NOT ON BOARD WITH THIS
SCENARIO. THE EUROPEAN CENTRE ENSEMBLE MEAN SUPPORTED THE DAY 3
POSITION OF THE DETERMINISTIC ECMWF...WHICH ADDED CREDIBILITY TO
THIS FEATURE. DECIDED TO DEPICT A MODEST LOW LIFTING THROUGH THE
WESTERN ATLANTIC FOR THE PRELIMINARY UPDATE...BASED ON THE
CONSIDERABLE BACKING FROM SEVERAL OF THE 00Z MODELS. WHETHER THIS
SYSTEM BECOMES TROPICAL IN NATURE...AND DEVELOPS AT ALL...IS NOT
CLEAR. WILL AWAIT THE MIDDAY COORDINATION CALL WITH TPC TO BEGIN
COMMITTING ONE WAY OR ANOTHER.
FINAL...
THOUGH THE 12Z DETERMINISTIC GFS HAS TRENDED STRONGLY TOWARD
HONORING THE BLOCK OVER EASTERN CANADA...AND ACKNOWLEDGING THE LOW
LIFTING ALONG THE EAST COAST...IT IS STILL AT ODDS WITH THE OTHER
GLOBAL MODELS IN MANY IMPORTANT WAYS WITH REGARD TO THE SHAPE OF
THE LONG WAVES AND THE WAY THE VARIOUS SHORT WAVES IN THE FLOW
INTERACT. THE 12Z GEFS MEAN WAS CLOSER TO THE GEM...UKMET...AND
ECMWF FROM THAT CYCLE...BUT THE BLEND USED IN THE UPDATE PACKAGE
STILL REPRESENTS AN EVEN BETTER REPRESENTATION OF THE PREFERRED
CLUSTER...SO MADE NO CHANGES FOR THE FINAL ISSUANCE OTHER THAN
SUBTLE ADJUSTMENTS TO THE TRACK OF THE LOW OFF THE ATLANTIC
SEABOARD. AM NOT FULLY SOLD ON THE INTENSITY OF THE SHORT WAVE
APPROACHING NORTHERN CALIFORNIA DURING THE FIRST HALF OF THE
PERIOD...CONSIDERING THE TIME OF YEAR...BUT ANY ENERGETIC IMPULSE
IMPACTING THAT REGION ALWAYS RAISES THE THREAT OF DRY LIGHTNING
DURING THE SUMMER...SO ITS CERTAINLY WORTH CONSIDERATION.
CISCO
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