286  
ACUS02 KWNS 031731  
SWODY2  
SPC AC 031730  
 
DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1130 AM CST SUN DEC 03 2017  
 
VALID 041200Z - 051200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EXTENDING FROM  
EASTERN OKLAHOMA AND WESTERN ARKANSAS TO THE MID MISSISSIPPI  
VALLEY...  
   
..SUMMARY
 
 
A FEW THUNDERSTORMS MAY PRODUCE STRONG, GUSTY WINDS FROM PARTS OF  
THE SOUTHERN PLAINS AND WESTERN ARKANSAS TO THE MID MISSISSIPPI  
VALLEY MONDAY EVENING.  
   
..SYNOPSIS
 
 
A PATTERN CHANGE WILL CONTINUE TO EVOLVE ACROSS MUCH OF NORTH  
AMERICA TODAY INTO MONDAY, GIVEN THE EXPECTATION FOR LARGE-SCALE  
AMPLIFICATION OF THE MID- TO UPPER-LEVEL FLOW. MODELS ARE IN GOOD  
AGREEMENT WITH THIS PATTERN CHANGE AND AMPLIFICATION, WITH A BROAD  
ZONE OF CYCLONIC MID-LEVEL FLOW EXPANDING EASTWARD ACROSS THE  
CENTRAL U.S. MONDAY, AS A POTENT IMPULSE LIFTS FROM THE CENTRAL  
PLAINS NORTHEASTWARD TO THE UPPER GREAT LAKES, AND ANOTHER DIVES  
SOUTH INTO THE DAKOTAS/UPPER MIDWEST MONDAY NIGHT. THE RESULTANT  
SURFACE PATTERN WILL FEATURE AN INTENSE DEEPENING CYCLONE  
(ESPECIALLY MONDAY NIGHT), TRACKING NORTHEAST ACROSS THE UPPER MS  
VALLEY TOWARD NORTHERN ONTARIO. STRENGTHENING WEST/SOUTHWESTERLY  
500-MB WINDS ACROSS OK/KS THROUGH THE MID MS/OH VALLEYS TO THE GREAT  
LAKES WILL SUPPORT AN ATTENDANT COLD FRONT SWEEPING EASTWARD FROM  
THE CENTRAL AND SOUTHERN PLAINS. BY 12Z TUESDAY, THE COLD FRONT  
SHOULD EXTEND FROM LOWER MI AND OH THROUGH THE MID SOUTH TO EAST AND  
SOUTH-CENTRAL TX.  
 
THE NEUTRAL ORIENTATION OF THE PARENT LARGE-SCALE TROUGH AND THE  
COMBINATION OF STRONGER FORCING FOR ASCENT, ATTENDANT TO THE  
PROGRESSIVE LEAD SHORTWAVE TROUGH AND TRACK OF THE SURFACE LOW,  
REMAINING NORTH OF MUCH OF THE MARGINAL SEVERE RISK WILL RESULT IN  
VEERING OF LOW-LEVEL WINDS ALONG AND AHEAD OF THE COLD FRONT. THIS  
SUGGESTS CONVECTIVE DEVELOPMENT SHOULD INITIALLY BE ALONG THE FRONT,  
WITH A TENDENCY FOR FORCING TO BECOME ANAFRONTAL MONDAY NIGHT,  
ESPECIALLY WITH SOUTHWARD EXTENT.  
 
AHEAD OF THE COLD FRONT, MODEST LOW-LEVEL MOISTURE (E.G., SURFACE  
DEW POINTS IN THE UPPER 50S AND LOWER 60S) WILL STREAM  
NORTH/NORTHEASTWARD DURING THE DAY. THIS COMBINED WITH LIMITED  
SURFACE HEATING (DUE TO WARM-SECTOR CLOUDINESS) AND THE PRESENCE OF  
WEAK LAPSE RATES SUGGESTS A NARROW CORRIDOR OF SURFACE-BASED CAPE  
AROUND 250-600 J/KG SHOULD MATERIALIZE FROM EASTERN OKLAHOMA AND THE  
ARK-LA-TEX TO THE MID MISSISSIPPI VALLEY. A THIN, LOW-TOPPED BAND  
OF THUNDERSTORMS IS EXPECTED TO DEVELOP BY LATE AFTERNOON OR EARLY  
EVENING HOURS AND ACCELERATE EASTWARD WITH THE FRONT. DESPITE THE  
MEAGER BUOYANCY, CONSIDERABLE LOW/MID-LEVEL FLOW UPWARDS OF 40-60 KT  
MAY SUPPORT A FEW STRONGER GUSTS IN THE MORE ROBUST CONVECTIVE  
ELEMENTS. IN ADDITION, THE STRENGTH OF LOW-LEVEL SHEAR SUGGESTS A  
TORNADO THREAT CANNOT BE RULED OUT. MARGINAL SEVERE PROBABILITIES  
WILL BE MAINTAINED GIVEN THE WEAK OVERALL INSTABILITY. SOME  
EXPANSION TO THE NORTH AND SOUTH WITH THE MARGINAL RISK AREA MAY BE  
NEEDED IN LATER OUTLOOKS. DESPITE WEAKER INSTABILITY INTO  
WEST-CENTRAL IL, STRONGER FORCING FOR ASCENT AND SOME POTENTIAL FOR  
SURFACE-BASED PARCELS SUGGEST A WIND THREAT COULD OCCUR, WHILE  
FARTHER SOUTH, GREATER BUOYANCY AND SUFFICIENT LOW-LEVEL SHEAR MAY  
SUPPORT A SEVERE STORM PRIOR TO THE CONVECTION BECOMING ANAFRONTAL.  
 
..PETERS.. 12/03/2017  
 

 
 
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