Prognostic Meteorological Discussion
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000
FXUS02 KWBC 270517
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1216 AM EST SAT DEC 27 2014

VALID 12Z TUE DEC 30 2014 - 12Z SAT JAN 03 2015


...ARCTIC AIR TO SETTLE EAST AND WEST OF THE DIVIDE...

AN AMPLIFICATION OF THE FLOW ACROSS NORTH AMERICA IS EXPECTED TO
DELIVER ARCTIC AIR INTO THE WESTERN UNITED STATES EARLY IN THE
MEDIUM RANGE, WITH A SIZABLE CHUNK FORCED ACROSS THE ROCKIES INTO
THE NORTHERN INTERMOUNTAIN REGION, GREAT BASIN, AND EVEN AREAS ON
THE PACIFIC SIDE OF THE CASCADES. THE GREATEST THERMAL ANOMALIES
SHOULD BE EAST OF THE CONTINENTAL DIVIDE DURING THE DAY, FOLLOWING
THE UPSLOPE CLOUDS AND PRECIPITATION AS THE BIG SURFACE HIGH OOZES
SOUTHWARD THROUGH THE HIGH PLAINS--ALL THE WAY TO WESTERN TEXAS BY
MID PERIOD. THOUGH NOT ARCTIC AIR, A CLOSING OF THE UPPER FLOW
OVER SOUTHERN CALIFORNIA AND THE DESERT SOUTHWEST WOULD FOCUS COLD
IN THOSE REGIONS, WITH REMARKABLY LOW SNOW LEVELS IN THE TERRAIN
TO THE EAST OF LOS ANGELES AND SAN DIEGO IF THE VORTEX SPINS UP
THERE. SOME OF THE GUIDANCE DRIVES THE VORTEX OFFSHORE--A MUCH
MILDER OUTCOME.

SOME OF THE COLD AIR IS EXPECTED TO DRIVE EASTWARD ACROSS THE
MIDWEST, REACHING THE MID ATLANTIC AND NORTHEAST. WHEN PART OF THE
SOUTHWESTERN TROUGH FINALLY BREAKS OFF AND EJECTS EASTWARD DAYS 6
AND 7, THE NORTHERN EDGE OF THE PRECIPITATION SHIELD IS APT TO BE
IN WINTRY FORM--SNOW, SLEET, OR FREEZING RAIN. MUCH AND MORE NEEDS
TO SHAKE OUT IN THE GUIDANCE BEFORE DETERMINING WHERE THE SNOW AND
ICE STRIPE IS PAINTED. FOR THIS FORECAST, RELIED LARGELY ON THE
EUROPEAN CENTRE ENSEMBLE MEAN FOR THE FRONTS AND PRESSURES, WITH A
BLEND OF THE ECENS MEAN, NAEFS MEAN, AND GMOS FOR THE TEMPERATURE
GRIDS.


CISCO

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