Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 200601
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 AM EST SAT DEC 20 2014

VALID 12Z TUE DEC 23 2014 - 12Z SAT DEC 27 2014

...A VERY ACTIVE HOLIDAY WEATHER PATTERN...


...GUIDANCE/PREDICTABILITY ASSESSMENTS...

THE WPC MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS
HAVE BEEN PRIMARILY DERIVED FROM A BLEND OF THE 12 UTC ECMWF
ENSEMBLE MEAN WITH SMALLER INPUT FROM THE 18 UTC GEFS MEAN AND 18
UTC GFS/12 UTC ECMWF TO ADD MORE DETAIL. THIS BLEND IS WELL
CLUSTERED NEAR GUIDANCE COMPOSITE EARLY IN THE PERIOD...BUT OFFERS
A BIT MORE AMPLITUDE AND DECENT WPC CONTINUITY THROUGH LATER NEXT
WEEK AT LONGER MEDIUM RANGE TIME SCALES. THIS STRATEGY SEEMS
CONSISTENT WITH UPSTREAM FLOW AMPLITUDE. RECENT DETERMINISTIC
MODEL RUN-RUN CONTINUITY ISSUES HAS IMPROVED ENOUGH TO NOW LEND
NEAR AVERAGE PREDICTABILITY LEVELS.


...PATTERN OVERVIEW AND SENSIBLE WEATHER HIGHLIGHTS/THREATS...

IT REMAINS EVIDENT THAT AN AMPLIFIED MID-UPPER LEVEL TROUGH AND
PCPN FOCUSING LEAD SURFACE LOW/FRONTAL SYSTEM WILL STEADILY
PROGRESS TO THE EAST-CENTRAL US TUE AS EMBEDDED IMPUSLES DIG TO
THE LEE OF AN AMPLIFIED ERN PACIFIC/WEST COAST RIDGE ALOFT. THE
SUPPORTING AND INCREASINGLY NEGATIVE-TILT TROUGH ALOFT WORKS OVER
THE ERN US AND OUT THROUGH THE NERN STATES INTO DAYS 4/5 WED/THU.
A THREAT EXISTS FOR ORGANIZED WINTER WEATHER IN LEAD FLOW OVER A
COOLED NRN NEW ENG AIRMASS MAINLY TUE ALONG WITH MORE PRONOUNCED
DEEP LOW INDUCED WRAP-AROUND SNOWS SPREADING FROM THE UPPER
MIDWEST AND GREAT LAKE STATES/MIDWEST TUE/WED WITH LAKE EFFECT
INTO CHRISTMAS. ACTIVITY WORKS MORE IN ERNEST OUT THROUGH THE
APPALACHIANS AND MAINLY INTERIOR NRN MID-ATLANTIC/NERN US ON
CHRISTMAS EVE AND CHRISTMAS.

MEANWHILE...NRN/NERN PACIFIC MID-UPPER TROUGH ENERGIES SHOULD DIG
SEWD THROUGH AN INITIAL DOWNSTREAM MEAN RIDGE TO SPREAD
DYNAMICS/PCPN TO THE PAC NW CHRISTMAS EVE AND FURTHER INLAND
ACROSS THE N-CENTRAL INTERMOUNTAIN WEST/ROCKIES CHRISTMAS INTO
NEXT FRI. THIS WILL INCLUDE A THREAT FOR LOCALLY HEAVY SNOWS
FOCUSING OVER FAVORED INLAND TERRAIN. THIS WRN US SYSTEM REACHES
THE CENTRAL US DAY 5/6 PROMPTING CYCLO/FRONTOGENESIS AND
PCPN/INFLOW RECOVERY OUT FROM THE GULF OF MEXICO IN THE WAKE OF
THE LEAD/EXITING ERN/NERN US STRONG LOW SYSTEM. THIS INCLUDES AN
OVERRUNNING WINTERY PCPN THREAT ON THE NW PERIPHERY OF THE OVERALL
PCPN SHIELD SPREADING NEWD FROM THE CENTRAL PLAINS TO THE GREAT
LAKES/OH VALLEY THEN INTERIOR NERN US...ALL OVERTOP WARM SECTOR
RAINS AHEAD OF FRONTAL PASSAGE.

SCHICHTEL

$$




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