801  
ACUS01 KWNS 051253  
SWODY1  
SPC AC 051252  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0652 AM CST SUN NOV 05 2017  
 
VALID 051300Z - 061200Z  
 
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF  
THE MO/IL BORDER TO WESTERN OHIO...  
 
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM  
SOUTHWESTERN MO TO NORTHWESTERN PA...  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE  
SLIGHT RISK AND EXTENDING OVER PARTS OF THE OZARKS...  
   
..SUMMARY
 
 
SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL, DAMAGING WINDS, AND A  
FEW TORNADOES WILL BE POSSIBLE FROM PARTS OF THE MID MISSISSIPPI  
VALLEY EAST-NORTHEASTWARD INTO THE LOWER GREAT LAKES THIS AFTERNOON  
INTO TONIGHT.  
   
..SYNOPSIS
 
 
IN MID/UPPER LEVELS, A BROAD SWATH OF ZONAL TO CYCLONIC FLOW IS  
EXPECTED TO COVER MOST OF THE CONTIGUOUS U.S. THIS PERIOD. WITHIN  
THAT, DISTINCT NORTHERN- AND SOUTHERN-STREAM SPEED MAXIMA WILL  
REMAIN APPARENT IN ROUGHLY THE 500-250-MB LAYER: A NORTHERN-STREAM  
JET AXIS ROUGHLY FROM THE PACIFIC NORTHWEST ACROSS LAKE SUPERIOR TO  
WESTERN QC, AND ITS SOUTHERN COUNTERPART FROM SOUTH-CENTRAL CA TO  
THE LOWER OHIO VALLEY. A POSITIVELY TILTED NORTHERN-STREAM  
SHORTWAVE TROUGH -- NOW LOCATED OVER THE MB/ON BORDER TO THE EXTREME  
EASTERN DAKOTAS -- SHOULD MOVE EASTWARD TO FAR NORTHERN ON AND THE  
MN ARROWHEAD BY 00Z, SHIFTING TO AN AXIS FROM THE EASTERN SHORE OF  
HUDSON BAY TO UPPER MI BY 12Z. TO ITS SOUTH, A SERIES OF VERY  
MINOR/LOW-AMPLITUDE PERTURBATIONS WILL TRAVERSE THE NORTHERN RIM OF  
THE SOUTHERN-STREAM JET. THE NET EFFECT WILL BE A BROAD AREA OF  
HEIGHT FALLS ACROSS THE GREAT LAKES, OHIO VALLEY AND MO.  
 
AT THE SURFACE, 11Z ANALYSIS SHOWED A COLD FRONT EXTENDING  
SOUTHWESTWARD FROM A WEAK FRONTAL-WAVE LOW OVER NORTHEASTERN/EAST-  
CENTRAL MO, TO ANOTHER LOW AND DRYLINE INTERSECTION NEAR PNC, TO  
NORTHWESTERN OK AND SOUTHEASTERN CO. A WARM FRONT EXTENDED FROM THE  
LOW ACROSS CENTRAL IL TO NORTHWESTERN OH. THE FRONTAL-WAVE LOW  
SHOULD REMAIN WEAK WHILE MIGRATING ALONG THE BOUNDARY TO SOUTHERN IN  
THROUGH THIS EVENING. BY 00Z THE COLD FRONT SHOULD EXTEND NEAR A  
LINE FROM TOL-IND-MVN-MKO-SPS-DHT. BY 12Z IT SHOULD REACH NORTHERN/  
WESTERN NY, SOUTHERN OH, WESTERN/CENTRAL KY, SOUTHWESTERN AR, AND  
WEST-CENTRAL TX.  
   
..MIDDLE MISSISSIPPI VALLEY TO LOWER GREAT LAKES
 
 
THE MAIN, RELATIVELY MINOR ADJUSTMENTS TO THE OUTLOOK FOR THIS CYCLE  
INCLUDE:  
1. TIGHTENING THE PROBABILITY GRADIENT ON THE NORTHWEST RIM OF THE  
OUTLOOK, IN DEFERENCE TO FORECAST FRONTAL POSITION/TIMING DURING THE  
MID/LATE-AFTERNOON CONVECTIVE CYCLE, WITH INCREASING CONFIDENCE  
IMBUED BY MORE CONSISTENT PROGS OF INITIATION LOCATION/TIMING;  
2. EXTENSION OF MAINLY THE MARGINAL SEVERE PROBABILITIES OVER MORE  
OF THE AR OZARKS BY EARLY EVENING, TO ACCOUNT FOR POSSIBLE  
BACKBUILDING OF CONVECTION ALONG THE FRONT - STORM THAT MAY REMAIN  
SURFACE-BASED FOR AT LEAST A COUPLE HOURS BEFORE BEING UNDERCUT BY  
THE FRONT.  
 
SCATTERED THUNDERSTORMS WITH SEVERE POTENTIAL ARE EXPECTED IN AT  
LEAST TWO PRIMARY EPISODES ACROSS THE OUTLOOK AREAS TODAY INTO THIS  
EVENING. THE POTENTIAL FROM EACH OVERLAPS SOMEWHAT, AND  
COLLECTIVELY THEY COMPRISE THE OUTLOOK AREAS AS A WHOLE.  
 
ROUND 1 -- A GRADUALLY DENSER CLUSTER OF INITIALLY ELEVATED  
CONVECTION WITH PRIMARILY HAIL POTENTIAL OVER PORTIONS OF IL/IN THIS  
MORNING, AS NOTED ABOVE. IN THE NEAR TERM, MAINLY SMALL HAIL WITH  
ISOLATED SEVERE MAY OCCUR; SEE SPC MESOSCALE DISCUSSION 1752 FOR  
MORE DETAILS. SOME OF THIS ACTIVITY MAY BECOME SURFACE-BASED ACROSS  
PARTS OF IN/OH MIDDAY INTO AFTERNOON, WITH AN INCREASING THREAT FOR  
DAMAGING GUSTS AND A TORNADO RISK POTENTIALLY DEVELOPING AS WELL.  
DESPITE THE WESTERLY COMPONENT OF NEAR-SURFACE WINDS, STRONG SPEED  
SHEAR AND ENOUGH DIRECTIONAL SHEAR ARE APPARENT FOR ENLARGED  
LOW-LEVEL HODOGRAPHS AND ASSOCIATED STORM-SCALE ROTATION POTENTIAL,  
ALBEIT POTENTIALLY WITH MESSY SUPERCELLULAR OR BOWING-SEGMENT  
CHARACTER AND EMBEDDED CIRCULATIONS POSSIBLE. CONVECTION SHOULD  
PROCEED GENERALLY EAST-NORTHEASTWARD INTO PARTS OF THE UPPER OHIO  
VALLEY, BEFORE OUTRUNNING THE MOST FAVORABLY UNSTABLE BOUNDARY  
LAYER.  
 
ROUND 2 -- DEVELOPMENT MID/LATE AFTERNOON NEAR THE COLD FRONT, FROM  
NEAR THE STL AREA EAST-NORTHEASTWARD CLOSE TO I-70 INTO IN, AS BOTH  
WARM ADVECTION AND DIABATIC HEATING FAVORABLY DESTABILIZE THE MOIST  
BOUNDARY LAYER BEHIND THE MORNING ACTIVITY. THIS ROUND MAY INCLUDE  
A DISCRETE SUPERCELL OR TWO WITH A FULL-SPECTRUM SEVERE RISK,  
INCLUDING SIGNIFICANT/DAMAGING HAIL. THE VERTICAL JUXTAPOSITION OF  
RELATIVELY MAXIMIZED LAPSE RATES ALOFT (THANKS TO EML PROXIMITY) AND  
PEAK BOUNDARY-LAYER LAPSE RATES YIELDS MLCAPE APPROACHING 2000 J/KG  
IN FORECAST SOUNDINGS, AMIDST 150-250 J/KG EFFECTIVE SRH AND 50-55  
KT EFFECTIVE-SHEAR MAGNITUDES, WITH ENOUGH OBLIQUELY CROSS-FRONTAL  
FLOW COMPONENT ALOFT TO SUGGEST A PERIOD OF SUPERCELL POTENTIAL  
BEFORE AN EVOLUTION TO QUASI-LINEAR MODE. THIS ACTIVITY SHOULD LAST  
INTO THE EVENING AND OVERNIGHT HOURS, SHIFTING EASTWARD/  
SOUTHEASTWARD ACROSS THE REMAINDER OF THE OUTLOOK AREAS, WITH  
BACKBUILDING EXPECTED ACROSS THE OZARKS REGION. THE MAIN THREAT  
SHOULD EVOLVE TO WIND WITH TIME, ISOLATED HAIL STILL BEING POSSIBLE,  
BEFORE SUBSTANTIAL WEAKENING OCCURS LATE TONIGHT.  
 
..EDWARDS/MOSIER.. 11/05/2017  
 

 
 
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