674  
FXUS01 KWBC 202018  
PMDSPD  
 
SHORT RANGE FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
417 PM EDT MON AUG 20 2018  
 
VALID 00Z TUE AUG 21 2018 - 00Z THU AUG 23 2018  
 
...HEAVY RAIN AND SEVERE WEATHER EXPECTED ACROSS THE MISSISSIPPI  
VALLEY THROUGH TONIGHT ...  
   
..ACTIVE WEATHER RETURNS FOR THE EAST COAST FOR THE COMING DAYS
 
 
...FIRE WEATHER AND AIR QUALITY CONCERNS CONTINUE FOR PORTIONS OF  
THE WESTERN U.S...  
 
A VERY STRONG LOW PRESSURE SYSTEM WILL CONTINUE TO LIFT ACROSS THE  
MID AND UPPER MISSISSIPPI VALLEY THIS EVENING, REACHING THE OHIO  
VALLEY AND LOWER GREAT LAKES BY OVERNIGHT. FROM THIS WILL STRETCH  
A ROBUST COLD FRONT WHICH WILL DRAPE SOUTHWARD INTO THE SOUTHERN  
PLAINS. AHEAD OF THE FRONTAL SYSTEM, WARM AND MOIST AIR WILL BE  
TRANSPORTED FROM THE GULF OF MEXICO SPAWNING WIDESPREAD SHOWERS  
AND THUNDERSTORMS ACROSS MUCH OF THE EASTERN U.S. AND SOUTHEAST.  
THE HEAVIEST RAINFALL AND BEST THUNDERSTORM POTENTIAL WILL BE  
LOCATED ALONG THE FRONTAL BOUNDARY AND CLOSE TO THE CENTER OF LOW  
PRESSURE. THE STORM PREDICTION CENTER HAS OUTLINED A PORTION OF  
THE MID/LOWER MISSISSIPPI RIVER AS BEING IN AN ENHANCED RISK OF  
SEVERE THUNDERSTORMS THROUGH TONIGHT. A SLIGHT RISK OF SEVERE  
WEATHER IS ALSO IN EFFECT FOR THE SURROUNDING AREAS. A SEVERE  
THUNDERSTORM WATCH IS IN EFFECT FOR NORTHEAST ARKANSAS, SOUTHEAST  
MISSOURI, AND SOUTHERN ILLINOIS. THE WEATHER PREDICTION CENTER HAS  
ALSO OUTLINED A LARGE SLIGHT RISK AREA FOR EXCESSIVE RAINFALL  
STRETCHING FROM THE LOWER MISSISSIPPI RIVER NORTHWARD TO LAKE  
MICHIGAN AND WESTWARD INTO IOWA THROUGH TONIGHT. FLOODING IS  
ONGOING ALONG THE MISSOURI RIVER IN NEBRASKA AND IOWA, AND FLASH  
FLOOD WATCHES HAVE BEEN ISSUED ACROSS SOUTHERN WISCONSIN AND A  
PORTION OF SOUTHERN VIRGINIA AND NORTH-CENTRAL NORTH CAROLINA. AS  
THIS SYSTEM CONTINUES TO PROGRESS EASTWARD OVER THE COMING DAYS,  
SO TO WILL THE SEVERE WEATHER AND FLASH FLOODING THREATS.  
MEANWHILE, BEHIND THIS SYSTEM, A LARGE AREA OF HIGH PRESSURE WILL  
SET IN ACROSS THE EASTERN U.S., RESULTING IN MUCH DRIER WEATHER TO  
FINISH OUT THE WORK WEEK.  
 
FIRE WEATHER RISKS WILL CONTINUE TO BE ELEVATED ACROSS THE WEST,  
ESPECIALLY FOR THE PACIFIC NORTHWEST, INTERMOUNTAIN WEST, GREAT  
BASIN, AND PORTIONS OF THE NORTHERN ROCKIES THROUGH TUESDAY. RED  
FLAG WARNINGS ARE IN EFFECT FOR PARTS OF THESE REGIONS DUE TO HIGH  
WINDS AND LOW RELATIVE HUMIDITIES. AIR QUALITY ALSO REMAINS A  
CONCERN DUE TO THE SMOKE FROM ONGOING FIRES. AIR QUALITY ALERTS  
REMAIN IN EFFECT FOR ALL OF WASHINGTON, OREGON, NORTHERN IDAHO,  
AND WESTERN MONTANA. FURTHERMORE, FIRES BURNING IN BRITISH  
COLUMBIA, CANADA ARE TRANSPORTING SMOKE SOUTHWARD INTO PORTIONS OF  
MINNESOTA, WHERE AN AIR QUALITY ALERT IS ALSO IN EFFECT.  
 
MONSOONAL MOISTURE WILL SURGE BACK INTO THE SOUTHWEST BY TUESDAY  
AND EXPAND ACROSS THE GREAT BASIN AND SOUTHERN/CENTRAL ROCKIES,  
RESULTING IN SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS  
THROUGH THE DAY. THESE STORMS WILL THEN SHIFT EASTWARD TO  
ENCOMPASS A PORTION OF THE CENTRAL AND SOUTHERN PLAINS BY MID  
WEEK. THE BEST SHOWER AND THUNDERSTORM POTENTIAL WILL BE IN THE  
AFTERNOON AND EARLY EVENING EACH DAY. SOME OF THESE STORMS COULD  
PRODUCE FLASH FLOODING, ESPECIALLY IN FAVORABLE TERRAIN AND URBAN  
AREAS, AS WELL AS ACROSS BURN SCAR REGIONS. FLASH FLOODING WILL  
ALSO BE A CONCERN IN THE HIGH PLAINS, WHERE ABOVE NORMAL RAINFALL  
HAS ALREADY OCCURRED OVER THE PAST WEEK.  
 
WIX  
 
GRAPHICS AVAILABLE AT  
WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP  

 
 
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