Prognostic Meteorological Discussion
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000
FXUS02 KWBC 231601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT MON OCT 23 2017

VALID 12Z THU OCT 26 2017 - 12Z MON OCT 30 2017

...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER/THREATS
HIGHLIGHTS...

MODELS AND ENSEMBLES SEEM IN REASONABLE OVERALL AGREEMENT THU/FRI
AS A WELL ORGANIZED LEAD SYSTEM EJECTS OFF THE ERN SEABOARD INTO
THE CANADIAN MARITIMES AND WRN ATLANTIC. THIS OCCURS AS A DYNAMIC
UPSTREAM MID-UPPER LEVEL TROUGH DIGS SEWD OVER THE N-CENTRAL US IN
RAPIDLY AMPLIFYING MID-UPPER LEVEL FLOW DOWNSTREAM OF A BUILDING
NORTH AMERICAN WEST COAST RIDGE. AN ASSOCIATED AND PCPN FOCUSING
SURFACE LOW DEVELOPS AND LIFTS ACROSS THE UPPER MIDWEST/GREAT
LAKES INTO ERN CANADA DURING THIS PERIOD...WITH ADDITIONAL
ACTIVITY ALONG/AHEAD OF A TRAILING COLD FRONT AS POST-FRONTAL COLD
HIGH PRESSURE SURGES RAPIDLY DOWN THROUGH THE W-CENTRAL US.

GUIDANCE FORECAST SPREAD INCREASES MORE SIGNIFICANTLY OVER THE
WEEKEND INTO EARLY NEXT WEEK...EVEN THOUGH THERE IS DECENT
AGREEMENT WITH THE IDEA OF SWINGING AN ELONGATED AND WIDESPREAD
RAINFALL FOCUSING FRONT ACROSS THE ERN US. POTENTIAL WAVE
DEVELOPMENT DETAILS ARE MORE UNCERTAIN...BUT OVERALL DOES SEEM
LIKELY GIVEN SUPPORTING MID-UPPER LEVEL TROUGH AMPLITUDE ALOFT.
MODELS AND ENSEMBLES ALSO INTRODUCE A THREAT OF A POTENTIAL
CARRIBEAN TROPICAL SYSTEM DEVELOPING AND LIFTING UP OFF THE ERN
SEABOARD IN ADVANCE OF THE WAVY AND SLOWLY EASTWARD PROGRESSING
FRONTAL SYSTEM. THIS WOULD HAVE SOME POTENTIAL TO DRASTICALLY
INCREASE AVAILABLE MOISTURE/PCPN INTO THE WRN ATLANTIC AND
POSSIBLY THE ERN US. SATELLITE IMAGERY DOES NOT HAVE A CLEAR
SIGNAL FOR DEVELOPMENT YET...BUT SOME MODELS INCLUDING ESPECIALLY
THE 00 UTC ECMWF/CANADIAN AND UKMET OFFER MORE ORGANIZED AND
INCREASINGLY FAST PROPAGATION THAN THE GFS...A WIDE VARIETY OF
ENSEMBLE MEMBERS...AND NHC/WPC CONTINUITY. WPC PROGS FOCUS
ACTIVITY WITH THE WAVY FRONT AND ARE MORE CONSERVATIVE WITH
TROPICAL DEVELOPMENTS PENDING INCREASED SATELLITE/GUIDANCE SIGNALS
AND ADDITIONAL NHC COLLABORATION.

OVERALL...WPC MEDIUM RANGE SURFACE FRONTS PRESSURES AND 500MB
PROGS WERE ACCORDINGLY DERIVED MAINLY FROM THE 00 UTC ECMWF
ENSEMBLE MEAN ALONG WITH SMALLER INPUTS FROM THE 06 UTC GFS/GEFS
AND 00 UTC ECMWF TO INCORPORATE SOME OF THE ENVELOPE OF GUIDANCE
SOLUTIONS.

SCHICHTEL

$$





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