019  
FXUS01 KWBC 190753  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
252 AM EST TUE DEC 19 2017  
 
VALID 12Z TUE DEC 19 2017 - 12Z THU DEC 21 2017  
 
...HEAVY RAIN POSSIBLE ALONG THE PACIFIC NORTHWEST COAST, WITH  
HEAVY SNOWFALL LIKELY IN THE CASCADES AND NORTHERN ROCKIES...  
 
...HEAVY RAINFALL AND FLASH FLOODING POSSIBLE ACROSS PORTIONS OF  
THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...  
 
COASTAL RAIN AND ELEVATION SNOWS ACROSS THE NORTHWEST WILL  
INCREASE IN COVERAGE TODAY AS A STRONG COLD FRONT PUSHES ONSHORE  
THIS MORNING. HEAVY SNOWFALL IS LIKELY ACROSS THE WASHINGTON AND  
OREGON CASCADES AS WELL AS PORTIONS OF THE NORTHERN ROCKIES.  
WINTER STORM WARNINGS ARE IN EFFECT IN THESE RANGES WHERE AS MUCH  
AS 1 TO 2 FEET OF SNOW IS FORECAST. AS THE COLD FRONT MOVES  
EASTWARD THROUGH THE WESTERN U.S. IT WILL USHER IN COLDER TEMPS  
WHICH MAY CHANGE RAINFALL IN THE LOWER ELEVATIONS TO SNOW OR A  
RAIN/SNOW MIX, INCLUDING SEATTLE. BY WEDNESDAY, THE MOISTURE  
SUPPLY WEAKENS BUT GENERALLY LIGHT ACCUMULATING SNOW WILL SPREAD  
INTO MUCH OF THE GREAT BASIN, THE ROCKIES, THE NORTHERN PLAINS,  
AND EVENTUALLY THE UPPER MISSISSIPPI VALLEY. EXPECT RAIN OR A RAIN  
SNOW MIX BY THURSDAY MORNING ACROSS PORTIONS OF THE CENTRAL PLAINS  
JUST TO THE NORTH OF A DEVELOPING SURFACE LOW.  
 
MEANWHILE, SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP TO  
THE NORTH OF A WARM FRONT LIFTING ACROSS THE GULF COAST STATES.  
HEAVY RAINFALL WILL BE POSSIBLE ALONG THE BOUNDARY FROM NORTHEAST  
TEXAS INTO SOUTHERN TENNESSEE TODAY, WHERE WPC IS HIGHLIGHTING A  
MARGINAL TO SLIGHT RISK FOR EXCESSIVE RAINFALL/FLASH FLOODING.  
ISOLATED SEVERE THUNDERSTORMS ARE ALSO POSSIBLE, AS PER THE LATEST  
CONVECTIVE OUTLOOK ISSUED BY THE STORM PREDICTION CENTER. HEAVY  
RAINFALL WILL SPREAD EASTWARD ACROSS THE TENNESSEE VALLEY AND INTO  
THE LOWER MID-ATLANTIC ON WEDNESDAY INTO THURSDAY AS A SURFACE LOW  
DEVELOPS ALONG THE FRONT AND SWEEPS EASTWARD THROUGH THE DEEP  
SOUTH.  
 
ELSEWHERE, LIGHT RAIN AND SNOW WILL BE POSSIBLE ACROSS THE  
NORTHEAST ASSOCIATED WITH A FRONTAL PASSAGE TODAY. THE ACTIVITY  
SHOULD WANE BY THIS EVENING BUT MAY LINGER INTO WEDNESDAY ACROSS  
PORTIONS OF THE GREAT LAKES AS WESTERLY FLOW AIDS IN SOME MAINLY  
LIGHT LAKE EFFECT SNOW SHOWERS DOWNWIND OF THE LAKES.  
 
SANTORELLI  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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