Prognostic Meteorological Discussion
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000
FXUS02 KWBC 230704
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST THU NOV 23 2017

VALID 12Z SUN NOV 26 2017 - 12Z THU NOV 30 2017

...GUIDANCE/UNCERTAINTY ASSESSMENT AND PATTERN/THREAT HIGHLIGHTS...

LEAD MID-UPPER LEVEL TROUGH AND SURFACE LOW/FRONTAL SYSTEM/MODEST
PCPN EJECTS FROM THE NERN US SUN TO THE CANADIAN MARITIMES BY
CYBER MON. MEANWHILE...THE UPSTREAM PATTERN REMAINS AMPLIFIED
ALOFT AS AN ENERGETIC ERN PACIFIC TROUGH THREATENS THE WEST COAST.
THE MODELS NO LONGER OFFER A WELL CLUSTERED ENVELOPE OF SOLUTIONS
WITH THE FORECAST STRENGTH/TIMING OF THIS FEATURE DAYS 3-7. MODEL
RUN TO RUN CONTINUITY BECAME ABYSMAL TODAY WITH THE GFS MORE
PROGRESSIVE THAN EARLIER RUNS AND THE ECMWF LESS PROGRESSIVE AND
MORE DIGGY/AMPLIFIED. GIVEN ABOVE NORMAL UNCERTAINTY...PREFER AN
ENSEMBLE MEAN APPROACH USING THE 12 UTC ECMWF ENSEMBLE MEAN AND TO
A MUCH LESSER EXTENT THE 18 UTC GEFS MEAN. CONSIDERING WATER VAPOR
FLOW/UPSTREAM FLOW AMPLITUDE AND CONTINUITY HOWEVER...OPTED TO
LEAN STRONGLY ON ECMWF ENSEMBLES THAT OFFER LESS PROGRESSION/MORE
AMPLITUDE THAN GEFS/NAEFS...ALBEIT NOT AS MUCH AS THE 12 UTC
ECMWF. THE NEWER 00 UTC ECMWF HAS EASED FROM 12 UTC ECMWF
AMPLITUDE. THIS FEATURE IS THE KEY TO THE SUBSEQUENT DOWNSTREAM
FLOW EVOLUTION NEXT WEEK IN A PATTERN THAT GUIDANCE SEEMS TO BE
EXTREMELY SENSITIVE TO THE DETAILS OF MID-UPPER LEVEL SUPPORT TO
LEAD TO SURFACE CYCLOGENESIS
AND ASSOCIATED MODESTLY EMERGING FRONT MOISTURE/PCPN FOCUS. THE
WPC SOLUTION WOULD PROVIDE UNSETTLED WEATHER AND PCPN SWATH SEWD
ACROSS THE WRN US MON INTO TUE...WITH IMPROVING WEATHER AND
WARMING OVER MUCH OF THE WEST IN ITS WAKE UNDER A BUILDING RIDGE
ALOFT. CONTINUED MID-UPPER LEVEL TROUGH EJECTION AND EXPANDING
POTENTIAL WILL THEN BE HIGHLIGHTED ACROSS THE CENTRAL TO ERN US
TUE-NEXT THU AT WHICH TIME NEW BUT UNCERTAIN PACIFIC ENERGIES
POTENTIALLY APPROACH THE WEST COAST.

SCHICHTEL

$$




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