Prognostic Meteorological Discussion
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FXUS02 KWBC 210654
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 AM EST SUN DEC 21 2014

VALID 12Z WED DEC 24 2014 - 12Z SUN DEC 28 2014

...AN ACTIVE HOLIDAY WEATHER PATTERN...

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

THE MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR AND
PREDICTABLE LARGER SCALE MID-UPPER LEVEL PATTERN EVOLUTION FOR
MUCH OF THE UPCOMING WEEK. THIS ACTIVE FLOW REGIME GRADUALLY
TRANSITIONS FROM HIGH TO MORE MODEST AMPLITUDE WITH TIME AS AT
LEAST THREE WELL DEFINED MID-UPPER LEVEL TROUGHS AND
ASSOCIATED/UNSETTLING LEAD SURFACE LOW/FRONTAL SYSTEMS AND PCPN
SWATHS PROGRESS STEADILY ACROSS THE LOWER 48.
THE MOST AMPLIFIED/DEEP LEAD SYSTEM WORKS ACROSS THE ERN/NERN US
INTO ERN CANADA CHRISTMAS EVE INTO CHRISTMAS ALONG WITH A SNOW
THREAT FROM THE GREAT LAKES STATES TO THE N-CENTRAL
APPALACHIANS/NRN INTERIOR NERN US AND A MORE MOIST/WARMED AIRMASS
IN ADVANCE OF FRONTAL APPROACH WITH HEAVIEST LEAD QPF POTENTIAL
OVER NEW ENGLAND. MEANWHILE...A SECOND SYSTEM BREACHES THE WEST
COAST/NW US THEN N-CENTRAL GREAT BASIN/ROCKIES CHRISTMAS EVE AND
CHRISTMAS. SUBSEQUENT ENERGY TRANSFER AND SYSTEM GENESIS OCCURS
OVER THE CENTRAL THEN ERN US FRI-NEXT SUN THAT MAY SUPPORT A
MODEST SWATH OF OVERRUNNING SNOW OVER THE N-CENTRAL US THEN
MIDWEST/GREAT LAKES AND NERN US. A THIRD SYSTEM HITS THE NW US
THEN N-CENTRAL INTERMOUNTAIN WEST/ROCKIES NEXT WEEKEND TO PROLONG
A WET PATTERN WITH A TERRAIN HEAVY SNOW THREAT FOCUS.

SURFACE SYSTEM FORECAST SPREAD AND SENSIBLE WEATHER EMPHASIS SHOWS
MORE VARIANCE/UNCERTAINTY THAN ALOFT OVERALL...BUT THE 12 UTC
ECMWF/ECMWF ENSEMBLE MEAN AND THE EXPERIMENTAL HIGH RESOLUTION 18
UTC GFS PARALLEL SOLUTIONS INTO DAY 5/FRI SEEM BEST CLUSTERED AND
THEIR COMPOSITE IS PREFERRED. A SOLUTION CLOSEST TO THE 12 UTC
ECMWF ENSEMBLE MEAN AND TO A LESSER EXTENT THE 12 UTC ECMWF HOLDS
ONTO A BIT MORE AMPLITUDE THAN THE 18 UTC GFS PARALLEL FRI THROUGH
NEXT WEEKEND. THIS SEEMS TO BETTER FIT UPSTREAM PACIFIC FLOW
AMPLIFICTAION SHOWN COMMONLY BY GUIDANCE BY THEN.

SCHICHTEL

$$





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