Prognostic Meteorological Discussion
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FXUS02 KWBC 210632
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 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...

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 HEAVIER
SNOW THREAT FROM THE GREAT LAKES/MIDWEST TO THE N-CENTRAL
APPALACHIANS AND INTERIOR NERN US AND A WETTENED/WARMED AIRMASS IN
ADVANCE OF FRONTAL APPROACH. A SECOND SYSTEM BREACHES THE WEST
COAST/NW US THEN N-CENTRAL GREAT BASIN/ROCKIES CHRISTMAS EVE AND
CHRISTMAS. SUBSEQUENT ENERGY TRANSFER AND SYSTEM REGENESIS OCCURS
OVER THE CENTRAL THEN ERN US FRI-NEXT SUN. A THIRD SYSTEM REACHES
THE NWRN US THEN N-CENTRAL INTERMOUNTAIN WEST/ROCKIES NEXT WEEKEND
TO PROLONG A WET PATTERN WITH TERRAIN FOCUSING HEAVY SNOW THREAT.


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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