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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0520Z Nov 22, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1220 AM EST SAT NOV 22 2014

VALID 12Z TUE NOV 25 2014 - 12Z SAT NOV 29 2014


...MORE ARCTIC AIR EARMARKED FOR THE UNITED STATES...

RELIED ON THE STRONG CORRELATION BETWEEN THE MIDDLE GROUND OF THE
12Z/21 ECENS AND NAEFS MEANS AS A SYNOPTIC GUIDE THIS FORECAST.
THE GLOBAL NUMERICAL MODELS HAVE CONVERGED ON THE SHARPENING OF A
LONGWAVE RIDGE OVER THE WEST AND ANOTHER LONGWAVE TROUGH OVER THE
EAST--WITH ARCTIC AIR SLATED TO ONCE AGAIN PLUNGE INTO THE
CONTIGUOUS UNITED STATES. THE BUILDING OF THE RIDGE OVER THE WEST
WILL TONE DOWN THE PRECIPITATION IN THE PACIFIC NORTHWEST AND
LEAVE MOST OF CALIFORNIA, THE GREAT BASIN, AND THE DESERT
SOUTHWEST HIGH AND DRY. LATE IN THE PERIOD, SOME ENERGY SEEMS
DESTINED TO BLEED INTO THE RIDGE, ALLOWING FOR A MODEST UPTICK IN
RAINFALL FROM NORTHERN CALIFORNIA TO WASHINGTON.

THE EVOLUTION OF THE FLOW OVER THE EAST DEPENDS LARGELY ON THE
INTERACTION BETWEEN TWO SIGNIFICANT SHORTWAVES. FIRST, A WAVE
EMERGING FROM THE GULF OF MEXICO OFF THE SOUTHEAST COAST. SECOND,
THE VORTEX DRAWING THE ARCTIC AIR INTO THE NATION. BOTH OF THESE
SYSTEMS HAVE THE POTENTIAL TO PRODUCE SNOWFALL. THE ATLANTIC WAVE
HAS VASTLY MORE MOISTURE AVAILABLE, BUT AIR COLD ENOUGH FOR SNOW
APPEARS AT THIS POINT TO LIKELY BE CONFINED TO THE NORTHWESTERN
EDGE OF ITS PRECIPITATION SHIELD. STILL, WITH THE BUSY HOLIDAY
TRAVEL TIME NEXT WEDNESDAY, ANY WINTER WEATHER IS A PLANNING
CONSIDERATION. THE COLD VORTEX, ON THE OTHER HAND, IS
MOISTURE-STARVED, THOUGH A SWATH OF LIGHT TO MODERATE SNOW ALONG
AND NORTH OF ITS TRACK WOULD FALL INTO MUCH LOWER BOUNDARY-LAYER
TEMPERATURES--A FACTOR IN ROAD CONDITIONS. ALSO, THE TRACK OF THE
FRIGID AIR ACROSS THE GREAT LAKES WILL NO DOUBT SET THE
LAKE-EFFECT MACHINE IN MOTION AGAIN.


CISCO