209  
FXUS01 KWBC 211955  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
255 PM EST WED FEB 21 2018  
 
VALID 00Z THU FEB 22 2018 - 00Z SAT FEB 24 2018  
 
...COLD AND UNSETTLED WEATHER IS EXPECTED OVER THE WEST INCLUDING  
SOME HEAVY SNOW OVER THE ROCKIES...  
 
...ADDITIONAL HEAVY RAINFALL AND WIDESPREAD CONCERNS FOR FLOODING  
WILL PERSIST ACROSS PARTS OF THE SOUTHERN PLAINS, LOWER  
MISSISSIPPI VALLEY AND THE OHIO VALLEY...  
 
...WARM TEMPERATURES ARE GENERALLY EXPECTED TO CONTINUE ACROSS A  
LARGE PORTION OF THE EAST...  
 
THE WESTERN U.S. WILL MAINLY BE COLD, BUT ALSO UNSETTLED THROUGH  
THE END OF THE WEEK, AS A SERIES OF IMPULSES DROPPING SOUTH ACROSS  
WESTERN NORTH AMERICA HELP TO REINFORCE A BROAD UPPER LEVEL TROUGH  
OF LOW PRESSURE. THIS WILL MAINTAIN BELOW NORMAL TEMPERATURES WITH  
MOST OF THE WEST SEEING HIGH TEMPERATURES ABOUT 10 TO 20 DEGREES  
BELOW NORMAL. THIS ENERGY WILL ALSO BRING THE THREAT FOR HEAVY  
SNOW ACROSS PARTS OF NORTHERN CALIFORNIA, THE GREAT BASIN AND THE  
CENTRAL ROCKIES AS THE ENERGY TRAVERSES THE INTERIOR OF THE WEST.  
 
UNFORTUNATELY, THESE IMPULSES OF ENERGY EJECTING DOWN ACROSS THE  
WEST AND THEN OUT INTO THE PLAINS WILL BE THE PRIMARY DRIVERS OF  
MULTIPLE ROUNDS OF HEAVY RAINFALL FARTHER OFF TO THE EAST. THIS  
WILL INCLUDE PORTIONS OF THE SOUTHERN PLAINS, LOWER MISSISSIPPI  
VALLEY AND OHIO VALLEY AS MULTIPLE WAVES OF LOW PRESSURE EJECT  
NORTHEAST UP ALONG A FRONTAL ZONE DRAPED ACROSS THE REGION. THIS  
ADDITIONAL RAINFALL WILL BE LARGELY FALLING ON SATURATED GROUND  
FROM RECENT HEAVY RAIN OVER THE LAST SEVERAL DAYS AND GOING BACK  
TO LAST WEEK IN SOME CASES. THEREFORE, THE THREAT FOR ADDITIONAL  
FLASH FLOODING AND MAIN STEM RIVER FLOODING WILL BECOME ENHANCED  
THROUGH THE REMAINDER OF THE WEEK.  
 
ASIDE FROM THE FOCUS FOR HEAVY RAINFALL, THE SAME AFOREMENTIONED  
FRONT IS MARKING THE DIFFERENCE FROM AN ABNORMALLY WARM AIRMASS IN  
PLACE ACROSS MUCH OF THE EAST WHERE TEMPERATURES ARE REACHING AS  
HIGH AS THE 70S AND 80S, AND A VERY COLD AIRMASS THAT HAS NOSED  
SOUTH DOWN ACROSS MUCH OF THE PLAINS WHERE TEMPERATURES ARE  
LOCALLY BELOW FREEZING AS MUCH AS 10 TO 20 DEGREES BELOW NORMAL.  
 
OVER THE NEXT COUPLE OF DAYS, SOME OF THE WARM AIR ACROSS  
ESPECIALLY THE NORTHEAST AND PARTS OF THE MID-ATLANTIC REGION WILL  
BE TEMPERED BY A MODESTLY COLDER AIRMASS BEHIND A FRONTAL PASSAGE  
LATER TONIGHT, BUT THIS BOUNDARY WILL STALL OUT FROM THE LOWER  
MISSISSIPPI VALLEY TO ACROSS THE TENNESSEE VALLEY AND INTO THE  
MID-ATLANTIC REGION ON THURSDAY BEFORE THEN GRADUALLY BEGINNING TO  
LIFT BACK NORTH AS A WARM FRONT BY FRIDAY AS A NEW AREA OF LOW  
PRESSURE LIFTS UP ACROSS THE MIDWEST. THIS WILL KEEP THE SOUTHEAST  
U.S. IN PARTICULAR QUITE WARM WITH MUCH ABOVE NORMAL TEMPERATURES  
THROUGH THE END OF THE WEEK.  
 
REGARDING THE THREAT OF WINTER WEATHER, THERE WILL BE THE APPROACH  
OF A WAVE OF LOW PRESSURE FROM THE TENNESSEE VALLEY ON THURSDAY  
THAT WILL ACTUALLY INTERACT WITH SUFFICIENT COLD AIR OVER PARTS OF  
THE UPPER OHIO VALLEY, FAR NORTHERN MID-ATLANTIC AND INTERIOR OF  
THE NORTHEAST FOR A STRIPE OF SOME ACCUMULATING SNOW AND ICE.  
MEANWHILE, THERE WILL ALSO BE A SWATH OF ACCUMULATING SNOW AND ICE  
ACROSS PORTIONS OF ESPECIALLY THE CENTRAL PLAINS, MIDWEST AND  
GREAT LAKES FOR THURSDAY AND FRIDAY AS LOW PRESSURE RIDES  
NORTHEAST UP ACROSS THE REGION.  
 
ORRISON  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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