656
FXUS02 KWBC 071906
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
305 PM EDT WED OCT 07 2009
VALID 12Z SAT OCT 10 2009 - 12Z WED OCT 14 2009
A PACIFIC JET WILL EVENTUALLY TAKE AIM FOR THE WEST COAST THIS
PERIOD...WHICH ACTS TO MOVE THE EASTERN PACIFIC RIDGE THROUGH THE
WESTERN PORTION OF THE CONTINENT...WHICH ESCORTS TROUGHING FROM
THE PLAINS THROUGH THE EAST INTO THE WESTERN ATLANTIC. THE MODEL
GUIDANCE IS IN GENERAL AGREEMENT ON THE EXPECTED LONGWAVE PATTERN.
HPC GENERALLY FOLLOWED A BLEND OF THE 00Z GFS AND ECMWF
SOLUTIONS... AS THE GEFS/ECMWF ENSEMBLE MEANS DEPICT LITTLE IN
LARGE SCALE SPREAD.
STARTING OFF OVER THE WEEKEND... A DEEP SURFACE LOW OVER ERN NEW
ENGLAND WILL DEPART QUICKLY AND PUSH ITS SURFACE COLD FRONT
THROUGH THE SOUTHEAST INTO THE GULF STREAM AND DOWN INTO THE GULF
OF MEXICO. MEANWHILE UPSTREAM... A LARGE DOME OF SURFACE HIGH
PRESSURE WILL EXTEND FROM THE OH/TN VLYS WEST TOWARD THE FRONT
RANGE OF THE ROCKIES... REALLY WEDGING SOUTH FROM THE NRN PLAINS
INTO THE SRN PLAINS.
BY MON INTO TUES... THE FIRST STORM SYSTEM FROM THE PAC WILL REACH
THE WEST COAST AND WILL BE FOLLOWED UP BY AN EVEN MORE IMPRESSIVE
SYSTEM WHICH SHOULD REALLY CRANK UP THE ONSHORE FLOW/PAC MOISTURE
TRANSPORT INTO THE WEST. THIS WILL COMPLETELY SHIFT/PUSH THE COLD
AREA OF HIGH PRESSURE COMPLETELY INTO THE PLAINS AND THEN
DOWNSTREAM INTO THE EAST. BEFORE THEN... AN IMPULSE ROUNDING THE
BASE OF THE UPPER TROUGH WILL INDUCE AN AREA OF LOW PRESSURE ALONG
THE SOUTHEAST COAST OR WHERE THE STALLED SURFACE BOUNDARY REMAINS.
THIS LOW WILL TRACK UP THE ERN SEABOARD OR JUST OFFSHORE AND
DEEPEN RAPIDLY... DUE TO THE PHASING OF UPPER STREAMS. COMPARED TO
YESTERDAY AT THIS TIME... THE 00Z GFS AND ECMWF ARE EXTREMELY
CLOSE WITH THIS FEATURE AND COLD SHOT ARRIVING INTO THE ERN
SECTION OF THE COUNTRY.
FINALLY BY NEXT WED... A MASSIVE DOME OF COLD HIGH PRESSURE WILL
SUPPLANT ITSELF OVER THE ERN THIRD OF THE COUNTRY... WHILE THE
RETURN FLOW AROUND THIS HIGH AND MARITIME AIR MASS/COLD FRONT WILL
BEGIN TO INVADE THE PLAINS/MS VLY AND THE CONSTANT ONSHORE FLOW
INTO THE WEST SHOULD GRADUALLY CURTAIL AS SURFACE RIDGING BEGINS
TO BUILD ACROSS THE REGION.
..12Z UPDATE
OVERALL THE 12Z GUIDANCE REMAINS IN SOLID SHAPE CONCERNING THE
UPCOMING ACTIVE PATTERN. HOWEVER... THIS IS ONE SIGNIFICANT TREND
CONCERNING THE SURFACE WAVE AND POTENTIAL DEVELOPMENT WITH THIS
FEATURE NEXT MON THROUGH TUES. THE 12Z GFS/UKMET ARRIVED AND
SUGGEST A MUCH MORE WESTWARD TREND ON THIS LOW OR A MORE
AMPLIFIED/PHASED FEATURE... WITH A SURFACE LOW POSITION OVER ERN
NEW ENGLAND 12Z TUES 10/13. THIS WOULD MEAN A MUCH MORE
SIGNIFICANT PRECIP EVENT TUES AND WED ACROSS THE ERN THIRD OF THE
COUNTRY. HOWEVER... THE 12Z CANADIAN/ECMWF REMAIN CONSISTENT WITH
THE 00Z GFS/ECMWF AND ECMWF MEAN AND EARLIER HPC THINKING ON A
MUCH MORE SUPPRESSED SYSTEM ACROSS THE SOUTHEAST ON TUES AND DEEP
CYCLOGENESIS DOWNSTREAM OF THE CANADIAN MARITIMES. OVERALL THIS
TREND BEARS WATCHING BUT NO SIGNIFICANT CHANGE TO THE PRELIM
FCST... HPC DID HEDGE TO THE WEST THE SURFACE LOW TRACK D5-7.
MUSHER
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