609  
FXUS01 KWBC 200800  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EST TUE NOV 20 2018  
 
VALID 12Z TUE NOV 20 2018 - 12Z THU NOV 22 2018  
 
...HEAVY RAIN POSSIBLE FOR PARTS OF NORTHERN CALIFORNIA AND  
PACIFIC NORTHWEST COAST WITH A SLIGHT RISK FOR EXCESSIVE RAINFALL  
OVER PARTS OF CENTRAL/SOUTHERN CALIFORNIA...  
 
...HEAVY SNOW POSSIBLE OVER THE SIERRAS AND LIGHT SNOW OVER THE  
CASCADES AND THE UPPER GREAT LAKES INTO PARTS OF THE NORTHEAST...  
 
...AIR QUALITY ALERTS FOR PARTS OF CALIFORNIA AND AIR STAGNATION  
ADVISORY FOR PARTS OF WASHINGTON STATE/IDAHO...  
 
...TEMPERATURES WILL BE 10 TO 15 DEGREES BELOW AVERAGE OVER PARTS  
OF THE UPPER GREAT LAKES...  
 
UPPER-LEVEL ENERGY OVER THE GREAT LAKES/OHIO VALLEY WILL MOVE  
EASTWARD OFF THE NORTHEAST COAST OVERNIGHT TUESDAY. THE ENERGY  
WILL AID IN DEVELOPING SNOW OVER THE GREAT LAKES INTO NORTHERN NEW  
ENGLAND AND RAIN OVER PARTS OF THE CENTRAL APPALACHIANS INTO  
SOUTHERN NEW ENGLAND ON TUESDAY. THE RAIN WILL MOVE OFF SOUTHERN  
NEW ENGLAND COAST BY TUESDAY EVENING AS THE RAIN OVER THE CENTRAL  
APPALACHIANS CHANGES OVER TO SNOW ENDING OVERNIGHT TUESDAY. THE  
SNOW OVER THE LOWER GREAT LAKES WILL END FOR SHORT TIME OVERNIGHT  
TUESDAY, TOO. THE SNOW OVER NORTHERN NEW ENGLAND WILL END BY LATE  
WEDNESDAY MORNING. IN ADDITION, A SECOND AREA OF UPPER-LEVEL  
ENERGY OVER WESTERN ONTARIO WILL MOVE EASTWARD TO NORTHERN NEW  
ENGLAND BY WEDNESDAY EVENING. SNOW WILL DEVELOP OVER PARTS OF THE  
NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY THAT WILL MOVE INTO THE  
UPPER GREAT LAKES ON TUESDAY EVENING. THE SNOW WILL CONTINUE TO  
MOVE EASTWARD TO THE LOWER GREAT LAKES/NORTHEAST BY WEDNESDAY  
AFTERNOON AND EXTEND INTO NORTHERN NEW ENGLAND BY WEDNESDAY  
EVENING.  
 
MEANWHILE, A THIRD AREA OF UPPER-LEVEL ENERGY OVER THE WESTERN  
GULF COAST/LOWER MISSISSIPPI VALLEY WILL MOVE EASTWARD OFF THE  
SOUTHEAST COAST OVERNIGHT TUESDAY. THE ENERGY WILL PRODUCE RAIN  
AND THUNDERSTORMS OVER PARTS OF THE WESTERN GULF COAST INTO PARTS  
OF THE SOUTHEAST AND WILL, LIKEWISE, END OVERNIGHT TUESDAY.  
ADDITIONALLY, A FOURTH AREA OF UPPER-LEVEL ENERGY OVER PARTS OF  
NORTHWESTERN MEXICO WILL MOVE EASTWARD TO TEXAS BY WEDNESDAY  
EVENING. THE ENERGY WILL PRODUCE RAIN OVER PARTS OF WESTERN TEXAS  
OVERNIGHT TUESDAY. THE ENERGY WILL ALSO DRAW MOISTURE FROM THE  
GULF OF MEXICO OVER THE WESTERN GULF COAST EARLY WEDNESDAY MORNING  
INTO EARLY THURSDAY MORNING (THANKSGIVING). RAIN WILL REDEVELOP  
OVER THE WESTERN GULF COAST ON WEDNESDAY EXPANDING INTO PARTS OF  
THE CENTRAL GULF COAST ON THANKSGIVING MORNING.  
 
FURTHERMORE, AIR QUALITY ALERTS ARE IN EFFECT OVER PARTS OF  
SOUTHERN CALIFORNIA UNTIL THE FIRES ARE EXTINGUISHED. LIGHT WIND  
AND A STRONG INVERSION WILL PERSIST THROUGH WEDNESDAY LEADING TO  
AIR STAGNATION ADVISORY ACROSS NORTH IDAHO AS WELL AS CENTRAL AND  
EASTERN WASHINGTON. THE ARRIVAL OF LIGHT PRECIPITATION AND A  
SUBTLE INCREASE IN WINDS WEDNESDAY AND WEDNESDAY NIGHT MAY IMPROVE  
POLLUTION DISPERSION FOR SOME AREAS ACROSS THE INLAND NORTHWEST.  
MEANTIME, A DEEP UPPER-LEVEL TROUGH WILL MOVE ONSHORE OVER THE  
WEST COAST EARLY WEDNESDAY INTO THURSDAY MORNING (THANKSGIVING).  
RAIN WILL DEVELOP ALONG THE WEST COAST EARLY WEDNESDAY MORNING AND  
EXPAND INLAND TO THE NORTHERN INTERMOUNTAIN REGION/GREAT BASIN BY  
THANKSGIVING MORNING. THERE IS A MARGINAL WITH EMBEDDED SLIGHT  
RISK OF EXCESSIVE RAINFALL OVER CALIFORNIA FROM WEDNESDAY MORNING  
INTO THURSDAY MORNING. AS THE TROUGH MOVES INLAND THE SNOW LEVELS  
WILL LOWER OVER THE CASCADES AND THE SIERRAS. SNOW WILL BEGIN  
OVER THE HIGHER ELEVATIONS OF THE CASCADES AND SIERRAS BY  
WEDNESDAY AFTERNOON CONTINUING INTO THURSDAY MORNING. OVERNIGHT  
WEDNESDAY, SNOW WILL DEVELOP OVER PARTS OF NORTHERN CALIFORNIA AND  
THE SOUTHERN CASCADES.  
 
ZIEGENFELDER  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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