596  
ACUS01 KWNS 241627  
SWODY1  
SPC AC 241625  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1125 AM CDT SUN SEP 24 2017  
 
VALID 241630Z - 251200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS  
AFTERNOON AND EVENING ACROSS PARTS OF THE UPPER MISSISSIPPI  
VALLEY...  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF  
THE SOUTHERN HIGH PLAINS...  
   
..SUMMARY
 
 
A FEW STRONG THUNDERSTORMS MAY IMPACT PARTS OF THE UPPER MISSISSIPPI  
VALLEY REGION AND PORTIONS OF THE SOUTHERN HIGH PLAINS LATE THIS  
AFTERNOON AND EVENING, ACCOMPANIED BY SOME RISK FOR SEVERE WEATHER.  
   
..SYNOPSIS
 
 
MUCH OF THE U.S. WILL REMAIN UNDER THE INFLUENCE OF AN AMPLIFIED  
SOUTHERN BRANCH OF SPLIT WESTERLIES EMANATING FROM THE MID-LATITUDE  
PACIFIC, WITH THE AXES OF EMBEDDED LARGE-SCALE RIDGING CENTERED NEAR  
THE ATLANTIC SEABOARD AND WEST OF THE PACIFIC COAST, AND LARGE-SCALE  
TROUGHING NEAR THE ROCKIES. MODELS SUGGEST THAT THE TROUGH WILL  
MAINTAIN A POSITIVE TO NEUTRAL TILT WITH LITTLE EASTWARD PROGRESSION  
THROUGH THIS PERIOD, BUT AN EMBEDDED CLOSED LOW WILL WEAKEN AND  
BECOME INCREASINGLY SHEARED WHILE SLOWLY ACCELERATING NORTHEAST OF  
THE EASTERN GREAT BASIN, INTO THE WYOMING ROCKIES BY LATE TONIGHT.  
 
A COLD FRONT ASSOCIATED WITH THE UPPER TROUGHING HAS ADVANCED  
EASTWARD THROUGH MUCH OF THE NORTHERN PLAINS, AND SOUTHWARD THROUGH  
THE CENTRAL HIGH PLAINS, WITH SOME FURTHER EASTWARD/SOUTHWARD  
PROGRESSION EXPECTED THROUGH 12Z MONDAY. IT APPEARS THAT AT LEAST  
ONE IMPULSE EMERGING FROM THE UPPER TROUGH MAY SUPPORT SOME FURTHER  
DEVELOPMENT OF A FRONTAL WAVE ACROSS PARTS OF WESTERN AND NORTHERN  
MINNESOTA INTO NORTHWEST ONTARIO LATER TODAY THROUGH TONIGHT.  
 
DUE TO THE MERIDIONAL NATURE OF THE FLOW ACROSS THE CENTRAL U.S.,  
LOWER/MID TROPOSPHERIC LAPSE RATES ARE GENERALLY WEAK TO THE EAST OF  
THE ROCKIES. ADDITIONALLY, HIGH MOISTURE CONTENT AIR (AS  
CHARACTERIZED BY SURFACE DEW POINTS AROUND 70F AND PRECIPITABLE  
WATER NEAR 2 INCHES) IS GENERALLY CONFINED TO PORTIONS OF THE GULF  
COAST STATES AND LOWER RIO GRANDE VALLEY. HOWEVER, SOUTHEASTERLY  
LOW-LEVEL FLOW WILL CONTINUE TO ADVECT INCREASINGLY MOIST AIR INTO  
THE SOUTHERN HIGH PLAINS, AND A NARROW TONGUE OF MID 60S+ F SURFACE  
DEW POINTS MAY ADVECT NORTHWARD AHEAD OF THE COLD FRONT, ACROSS THE  
UPPER MISSISSIPPI VALLEY TODAY THROUGH TONIGHT. THIS MAY CONTRIBUTE  
TO MODEST DESTABILIZATION WHICH COULD SUPPORT SOME RISK FOR VIGOROUS  
THUNDERSTORM DEVELOPMENT WITH SOME SEVERE WEATHER POTENTIAL.  
   
..UPPER MISSISSIPPI VALLEY
 
 
A BELT OF STRENGTHENING SOUTHWESTERLY FLOW ASSOCIATED WITH THE  
IMPULSE EMERGING FROM THE UPPER TROUGHING APPEARS LIKELY TO REMAIN  
MOSTLY TO THE COOL SIDE OF THE EASTWARD ADVANCING COLD FRONT FRONT,  
PARTICULARLY IN THE MID/UPPER LEVELS. HOWEVER, IT STILL APPEARS  
THAT A NARROW CORRIDOR OF STRONGER PRE-FRONTAL BOUNDARY LAYER  
HEATING AND MOISTENING COULD CONTRIBUTE TO MODEST DESTABILIZATION,  
AND A WINDOW OF OPPORTUNITY FOR VIGOROUS THUNDERSTORM DEVELOPMENT IN  
THE PRESENCE OF 30-40+ KT 850-500 MB FLOW. AT THE PRESENT TIME THIS  
SEEMS MOST PROBABLE DURING THE 23-03Z TIME FRAME ACROSS PARTS OF  
CENTRAL/EASTERN MINNESOTA, WHERE STRONGER STORMS MAY BE ACCOMPANIED  
BY MAINLY A RISK FOR LOCALIZED POTENTIALLY DAMAGING WIND GUSTS.  
   
..PARTS OF THE SOUTHERN HIGH PLAINS
 
 
AT LEAST LOWER/MID 60S SURFACE DEW POINTS ARE EXPECTED TO BE  
MAINTAINED ON SOUTHEASTERLY LOW-LEVEL FLOW INTO/ACROSS THE PECOS  
VALLEY INTO THE WESTERN SLOPES OF THE DAVIS/SACRAMENTO MOUNTAINS OF  
SOUTHWEST TEXAS AND SOUTHERN NEW MEXICO. COUPLED WITH INSOLATION,  
THIS MAY CONTRIBUTE TO THE DEVELOPMENT OF MODEST BOUNDARY LAYER CAPE  
BY LATE AFTERNOON. BENEATH MODERATE TO STRONG CYCLONIC,  
SOUTHWESTERLY MID/UPPER FLOW, A WINDOW OF OPPORTUNITY APPEARS TO  
EXIST FOR THE ENVIRONMENT TO BECOME CONDUCIVE TO THE FORMATION OF AN  
ISOLATED SUPERCELL OR TWO EARLY THIS EVENING.  
 
..KERR/PICCA.. 09/24/2017  
 

 
 
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