Prognostic Meteorological Discussion
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FXUS01 KWBC 182027
PMDSPD

SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 PM EST MON DEC 18 2017

VALID 00Z TUE DEC 19 2017 - 00Z THU DEC 21 2017

...HEAVY SNOW POSSIBLE OVER THE CASCADES AND NORTHERN ROCKIES...

...HEAVY RAIN POSSIBLE OVER PARTS OF THE PACIFIC NORTHWEST COAST...

...HEAVY RAIN POSSIBLE OVER PORTIONS OF THE SOUTHERN PLAINS INTO
THE SOUTHERN APPALACHIANS...

ONSHORE FLOW AHEAD OF THE NEXT SYSTEM WILL AID IN PRODUCING RAIN
AND HIGHEST ELEVATION SNOW OVER PARTS OF THE PACIFIC NORTHWEST AND
SNOW AND LOWER ELEVATIONS RAIN OVER PARTS OF THE NORTHERN
INTERMOUNTAIN REGION/NORTHERN ROCKIES THROUGH TUESDAY MORNING.  ON
TUESDAY THE NEXT SYSTEM WILL BEGIN TO MOVE ONSHORE OVER THE
PACIFIC NORTHWEST MOVING INLAND TO THE NORTHERN ROCKIES/GREAT
BASIN AND PARTS OF CENTRAL CALIFORNIA BY WEDNESDAY.  THE SNOW
LEVELS WILL DECREASE OVER THE NORTHWEST AS THE ASSOCIATED FRONT
MOVES INLAND, LOWERING TO THE COAST OVER PARTS OF NORTHWESTERN
WASHINGTON STATE.  RAIN AND HIGHER ELEVATIONS SNOW WILL DEVELOP
OVER THE NORTHWEST AND SNOW OVER THE NORTHERN INTERMOUNTAIN
REGION/NORTHERN ROCKIES ON TUESDAY.  RAIN AND HIGHER ELEVATION
SNOW BEGINS TO MOVE INTO NORTHERN CALIFORNIA BY TUESDAY EVENING
THAT WILL EXPAND INTO CENTRAL CALIFORNIA AND SNOW IN THE GREAT
BASIN OVERNIGHT TUESDAY INTO WEDNESDAY.  IN ADDITION, SNOW WILL
BEGIN TO DEVELOP OVER PARTS OF THE NORTHERN PLAINS ALSO OVERNIGHT
TUESDAY INTO WEDNESDAY.

MEANWHILE, AN UPPER-LEVEL LOW OVER NORTHWESTERN MEXICO WILL MOVE
NORTHEASTWARD TO THE LOWER MISSISSIPPI VALLEY BY WEDNESDAY WHILE
WEAKENING.  MOISTURE FROM THE WESTERN GULF OF MEXICO WILL STREAM
NORTHWARD OVER THE SOUTHERN PLAINS INTO PARTS OF THE LOWER
MISSISSIPPI VALLEY AND INTO THE SOUTHEAST BY WEDNESDAY MORNING.
THE MOISTURE AND UPPER-LEVEL ENERGY WILL AID IN PRODUCING SHOWERS
AND THUNDERSTORMS OVER PARTS OF THE WESTERN GULF COAST/SOUTHERN
PLAINS THAT WILL BEGIN TO EXPAND EASTWARD INTO THE LOWER
MISSISSIPPI VALLEY BY TUESDAY MORNING.  ON TUESDAY, THE SHOWERS
AND THUNDERSTORMS WILL CONTINUE TO EXPAND EASTWARD INTO PARTS OF
THE TENNESSEE VALLEY/SOUTHEAST WELL INTO WEDNESDAY MORNING.

MORE TO FOLLOW





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