856
FXUS02 KWBC 201802
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
201 PM EDT THU AUG 20 2009
VALID 12Z SUN AUG 23 2009 - 12Z THU AUG 27 2009
MULTI-DAY MEANS BASED ON LATEST OPERATIONAL MODEL AND ENSEMBLE
MEAN GUIDANCE MAINTAIN GOOD CONTINUITY IN DEPICTING A STABLE LARGE
SCALE PATTERN CONSISTING OF A FAIRLY DEEP NERN PAC TROF... CNTRL
NOAM RIDGE... AND EXTREME ERN NOAM TROF. GOOD AGREEMENT WITH THE
EXPECTED LARGE SCALE FLOW FAVORS A CONSENSUS/BLEND APPROACH TO THE
MEDIUM RANGE FCST.
OVER THE WEST... THERE IS FAIRLY GOOD CLUSTERING WITH A SHRTWV
THAT SHOULD REACH THE PAC NW/WRN CANADA BY DAY 5 TUE. HOWEVER THE
GFS BRINGS LOWER HGTS INTO THE WEST COMPARED TO MOST OTHER
MODEL/ENSEMBLE MEAN SOLNS BY DAY 7 THU. AHEAD OF THIS DAYS 5-7
EVOLUTION THERE IS REASONABLE AGREEMENT WITH A DAY 3 SUN PAC
NW/WRN CANADA SHRTWV THAT SHOULD TRAVEL ACROSS SRN CANADA/EXTREME
NRN CONUS AND HELP TO RELOAD THE ERN NOAM MEAN TROF... THOUGH AT A
LATITUDE FARTHER NWD THAN THE ERN TROF EXISTING AT THE START OF
THE PERIOD. A BLEND OF THE BEST OPERATIONAL CLUSTER CAPTURES THE
ASSOC LOW PRESSURE WELL WITH ENSEMBLE MEANS LAGGING IN
DEFINITION... ESPECIALLY THE 00Z GEFS MEAN.
OVER THE EAST... THE GFS AND ECMWF ARE AT TWO EXTREMES IN REGARD
TO THE CORE OF MID LVL ENERGY AS OF EARLY DAY 3 SUN. THE ECMWF
MAY BE A LITTLE TOO FAR SWD WITH ITS UPPER LOW AT THAT TIME BUT A
FAIRLY GOOD CONSENSUS OF SHORT/MEDIUM RANGE GUIDANCE SUGGESTS THE
GFS IS TOO QUICK TO EJECT ENERGY ACROSS THE NORTHEAST. AS A
RESULT EXPECT A SLOWER DEPARTURE OF A FRONTAL WAVE FROM OFF THE
NRN MID ATLC/SRN NEW ENGLAND COAST VERSUS THE GFS/GEFS MEAN. BY
DAY 7 THU THE GFS ALSO BECOMES A LITTLE DEEPER WITH PORTIONS OF
THE ERN CANADA/NERN CONUS TROF THAN MOST OTHER GUIDANCE.
FARTHER S AND E... REMAINING INITIAL ERN TROF ENERGY IS EXPECTED
TO BE LEFT BEHIND OVER THE SOUTHEAST AND BE DIRECTED TOWARD THE
LOWER MS VALLEY/WRN GULF REGION IN RESPONSE TO EVOLUTION OF THE
RIDGE TO THE WEST. OVER THE WRN ATLC EXPECT HURCN BILL TO BE OFF
THE NEW ENGLAND COAST BY DAY 3 SUN... WITH MANUAL FCST BASED ON
THE 06Z TPC ADVISORY.
DAYS 3-5 SUN-TUE START WITH A BLEND OF THE 00Z
ECMWF/UKMET/CANADIAN TO CAPTURE THE MOST AGREEABLE ASPECTS OF THAT
PORTION OF THE FCST AND DOWNPLAY LOWER CONFIDENCE DETAILS OF ANY
INDIVIDUAL RUN. THEN DAYS 6-7 WED-THU USE AN EVEN BLEND OF THE
ECWMF/00Z ECMWF ENSEMBLE MEAN TO ACCOUNT FOR INCREASED UNCERTAINTY
AT THAT TIME FRAME... AS THE GEFS MEAN LACKS DEFINITION WITH THE
SYSTEM CROSSING SRN CANADA.
12Z GUIDANCE RUNS CONTINUE REASONABLE CONTINUITY. NO CHANGES TO
AFTN FINALS.
TROPICS..HURCN BILL MOVES NWD GETTING AS FAR WEST 68W-69W WITH
VERY HEAVY SWELL AND SURF IMPACTING THE EAST COAST WITH HIGHER
WINDS AND SEAS AFFECTING NEW ENGLAND AND INTO MARITIME CANADA DAYS
3 AND 4. CHI VELOCITY ANOMALY INDICATES THAT THE ATLANTIC BECOME
RELATIVELY UNFAVORABLE FOR ADDITIONAL DEVELOPMENT WITH SOME
CONSENSUS OF A WAVE MOVING THE BAHAMAS REGION LATE PERIOD BUT THE
EPAC WILL BE UNDER HIGHLY FAVORABLE CONDITIONS AND MODELS GENERATE
AT LEAST 3 SYSTEMS IN THE MEDIUM RANGE TIME FRAME.
A MONSOONAL RAINFALL PATTERN REMAINS OVER SOUTHWESTERN CONUS INTO
NEXT WEEK.
RAUSCH/ROSENSTEIN
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