841  
ACUS01 KWNS 041938  
SWODY1  
SPC AC 041937  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0137 PM CST MON DEC 04 2017  
 
VALID 042000Z - 051200Z  
 
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS  
AFTERNOON AND EVENING ACROSS PARTS OF EASTERN OKLAHOMA AND NORTHWEST  
ARKANSAS THROUGH MISSOURI...EASTERN IOWA...NORTHWESTERN ILLINOIS AND  
SOUTHWESTERN WISCONSIN...  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS  
SURROUNDING AREAS OF THE PLAINS AND OZARK PLATEAU INTO THE UPPER  
MIDWEST...  
   
..SUMMARY
 
 
ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED ACROSS EASTERN  
OKLAHOMA AND THE ARK-LA-TEX REGION, NORTHWARD ACROSS MISSOURI INTO  
PORTIONS OF THE UPPER MIDWEST, LATE THIS AFTERNOON INTO TONIGHT.  
   
..20Z OUTLOOK UPDATE
 
 
SEVERE WEATHER CATEGORICAL AND PROBABILISTIC AREAS HAVE BEEN  
EXPANDED WESTWARD SOME TO ACCOUNT FOR THE CURRENT FRONTAL POSITION,  
AND SOME LINGERING UNCERTAINTY CONCERNING EXACT TIMING OF STORM  
INITIATION LATE THIS AFTERNOON. THE AXIS OF STRONGEST PRE-FRONTAL  
SURFACE HEATING CURRENTLY EXTENDS NORTHWARD NEAR/EAST OF  
BARTLESVILLE, OK THROUGH THE CHILLICOTHE, MO AREA, AND SEEMS LIKELY  
TO PROVIDE THE FOCUS FOR STRONGEST STORM DEVELOPMENT THROUGH EARLY  
EVENING. MODEST BOUNDARY LAYER DESTABILIZATION IS ALSO ONGOING  
WITHIN A NARROW PRE-FRONTAL CORRIDOR AS FAR NORTH AS THE DEEPENING  
SURFACE LOW CENTER, NOW NEAR MINNEAPOLIS, AND SEVERE CATEGORICAL/  
PROBABILISTIC LINES HAVE BEEN EXPANDED NORTHWARD THROUGH THE UPPER  
MIDWEST TO ACCOUNT FOR THIS.  
 
..KERR.. 12/04/2017  
   
PREV DISCUSSION
 
/ISSUED 1027 AM CST MON DEC 04 2017/  
   
..SYNOPSIS
 
 
A SURFACE CYCLONE IN SOUTHWEST MN THIS MORNING WILL MOVE TOWARD LAKE  
SUPERIOR BY TONIGHT, WITH RAPID DEEPENING EXPECTED IN RESPONSE TO  
STRONG DEEP-LAYER FORCING FOR ASCENT WITHIN THE LEFT EXIT REGION OF  
A 130 KT UPPER JET STREAK. AN ASSOCIATED SURFACE COLD FRONT WILL  
SURGE SOUTHEASTWARD IN THE WAKE OF THE CYCLONE AND CROSS THE MID MS  
VALLEY AND SOUTHERN PLAINS BY THE END OF THIS FORECAST PERIOD. IN  
ADVANCE OF THE COLD FRONT, A NARROW MOIST SECTOR WITH BOUNDARY-LAYER  
DEWPOINTS IN THE MID 50S INTO IA AND MID-UPPER 60S IN TX, WILL  
CONTINUE TO SPREAD NORTHEASTWARD THROUGH THE DAY. THOUGH SURFACE  
HEATING WILL BE TEMPERED BY WIDESPREAD CLOUDS, THE LOW-LEVEL  
MOISTURE AND REMNANT STEEP MIDLEVEL LAPSE RATES WILL SUPPORT AT  
LEAST WEAK SURFACE-BASED BUOYANCY AS FAR NORTHEAST AS PARTS OF  
IA/IL.  
   
..MID MS VALLEY TO THE OZARKS THROUGH TONIGHT
 
 
THUNDERSTORM DEVELOPMENT IS EXPECTED IN A BAND ALONG THE COLD FRONT  
FROM MID-LATE AFTERNOON (21-23Z). IT APPEARS THERE WILL BE A 2-4  
HOUR WINDOW OF OPPORTUNITY FOR DAMAGING WINDS (AND PERHAPS AN  
ISOLATED TORNADO) THIS EVENING AS FAR NORTHEAST AS SOUTHEAST IA AND  
NORTHWEST IL, GIVEN BUOYANCY ROOTED AT THE SURFACE AND 50-60 KT FLOW  
JUST ABOVE THE SURFACE. STRONG DEEP-LAYER SHEAR MAY SUPPORT  
EMBEDDED SUPERCELLS WITHIN THE LINE FOR A FEW HOURS THIS EVENING.  
THE FRONTAL CONVECTION WILL MAINTAIN INTENSITY LONGER FROM EASTERN  
OK INTO AR, WHERE MID 60S DEWPOINTS WILL DRIVE AT LEAST WEAK  
BUOYANCY INTO TONIGHT. HOWEVER, THE CONVECTION WILL BECOME MORE  
ANAFRONTAL WITH TIME AND LOW-LEVEL FLOW WILL VEER/WEAKEN, WHICH WILL  
LIMIT THE SOUTHWESTWARD EXTENT OF ANY SEVERE-STORM THREAT.  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SPC Page Main Text Page