SPC AC 051946

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0246 PM CDT FRI SEP 05 2014

   VALID 052000Z - 061200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MIDWEST...

   ...SUMMARY...
   SCATTERED STRONG TO ISOLATED SEVERE STORMS WILL PRODUCE DAMAGING
   WINDS AND MARGINALLY SEVERE HAIL ACROSS PARTS OF THE MIDWEST THROUGH
   THIS EVENING.

   ...MIDWEST...
   PREVIOUS FORECAST REASONING REMAINS LARGELY ON-TRACK. MAIN CHANGE TO
   SLIGHT RISK AREA IS TO REFINE BASED ON CURRENT FRONTAL POSITION
   /WITH ONGOING STRONG STORMS OVER CHICAGOLAND/. MODIFIED 18Z DTX RAOB
   SAMPLED A VERY UNSTABLE AIR MASS AHEAD OF THE FRONT WITH LARGE
   BUOYANCY AMIDST MID-LEVEL LAPSE RATES AROUND 7 DEG C/KM. WITH THE
   BULK OF STRONGER FLOW CONCENTRATED IN THE LOWER PORTION OF THE
   TROPOSPHERE...PRIMARY HAZARD SHOULD REMAIN DAMAGING WINDS WITHIN
   SHORT-LINE SEGMENTS AND CLUSTERS THAT EVOLVE ACROSS THE REGION INTO
   THIS EVENING.

   ..GRAMS.. 09/05/2014

   .PREV DISCUSSION... /ISSUED 1108 AM CDT FRI SEP 05 2014/

   ...SYNOPTIC SETUP...
   RIDGE WILL REMAIN IN PLACE FROM THE SRN RCKYS ENE TO THE WRN
   ATLANTIC...S OF BROAD CYCLONIC FLOW OVER CNTRL/ERN CANADA. WITHIN
   THE LATTER FLOW...POSITIVE-TILT TROUGH NOW OVER WRN ONT EXPECTED TO
   CONTINUE ENE ONTO QUE TNGT/EARLY SAT...WHILE TRAILING/POSITIVE-TILT
   IMPULSE NOW OVER WRN NEB CONTINUES ENE TO WI/IA THIS EVE...AND TO LK
   HURON EARLY SAT.  

   AT THE SFC...COLD FRONT ASSOCIATED WITH ONT TROUGH SHOULD ADVANCE
   STEADILY ESE ACROSS LWR MI AND THE MID-MS VLY TODAY. A WEAK WAVE MAY
   FORM ALONG THE BOUNDARY OVER IL/IND/SRN MI TNGT IN RESPONSE TO
   NEB/IA IMPULSE. 

   ...ERN MO/MIDWEST/LWR MI THIS AFTN INTO TNGT...
   SET-UP APPEARS FAVORABLE FOR THE DEVELOPMENT OF LINES/SMALL CLUSTERS
   OF MAINLY MULTICELL STORMS FROM PARTS OF THE MID-MS VLY ENE INTO LWR
   MI AND THE LWR GRT LKS LATER TODAY INTO TNGT AS SFC HEATING FURTHER
   DESTABILIZES CORRIDOR OF 1.75+ INCH PW ALONG/AHEAD OF COLD FRONT. 

   EXTRAPOLATION OF MORNING RAOB DATA SUGGESTS THAT RESIDUAL EML/STEEP
   MID-LVL LAPSE RATE PLUME SPREADING ENE ON NRN SIDE OF UPR RIDGE WILL
   OVERLIE SRN LWR MI/NRN IND AND WRN/NRN OH THIS AFTN. ONCE CONVECTIVE
   TEMPS HAVE BEEN REACHED...FRONTAL UPLIFT AND...IN CNTRL LWR
   MI...UPLIFT ALONG PRE-FRONTAL OUTFLOW BOUNDARY...SHOULD OVERCOME
   CINH TO FOSTER STRONG STORM DEVELOPMENT. DEVELOPMENT IN MO/IL ALSO
   MAY BE ENCOURAGED BY THE APPROACH OF NEB/IA UPR IMPULSE.

   DEEP...LARGELY UNIDIRECTIONAL WSW FLOW WILL MINIMIZE CONVERGENCE. 
   BUT STORMS THAT DO FORM WILL POSE A CONDITIONAL RISK FOR DMGG WIND
   AND POSSIBLY SVR HAIL GIVEN VERY WARM/HUMID NEAR-SFC
   ENVIRONMENT...EML...AND 30-35 KT 700-500 MB FLOW THAT COULD YIELD
   SMALL BOWS/ARCING LINE SEGMENTS. ALTHOUGH THE STRONGEST STORMS
   SHOULD OCCUR BEFORE MID-LATE EVE...STRONG ACTIVITY COULD PERSIST
   INTO LATE TNGT/EARLY SAT OVER OH AND THE LWR GRT LKS.  

   ...S-CNTRL PLNS THIS AFTN/EVE...
   UPR AIR PATTERN IS SUCH THAT MID-LVL LAPSE RATES WILL BE RELATIVELY
   WEAK ALONG AND N OF THAT PART OF COLD FRONT ADVANCING SE ACROSS THE
   SRN PLNS TODAY/TNGT. WHILE NRN OK WILL BE GLANCED BY SRN FRINGE OF
   NEB/IA UPR IMPULSE...LARGE-SCALE FORCING FOR ASCENT OVER MOST OF THE
   REGION WILL REMAIN NEUTRAL AT BEST. COUPLED WITH MODEST CLOUD-LAYER
   SHEAR /AOB 30 KTS/...THE PROSPECTS FOR ORGANIZED/SUSTAINED SVR
   STORMS APPEAR LOW. NEVERTHELESS...FRONTAL UPLIFT AMIDST PW AOA 1.75
   INCHES AND DIURNALLY-STEEPENED LOW-LVL LAPSE RATES MAY YIELD A FEW
   STORMS WITH A POTENTIAL FOR BRIEFLY SVR WIND/HAIL.

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