MESOSCALE DISCUSSION 1859
   NWS STORM PREDICTION CENTER NORMAN OK
   0452 PM CDT SUN SEP 08 2013

   AREAS AFFECTED...PORTIONS OF SERN MT...CNTRL/SRN ND...WRN/CNTRL
   SD...NERN/E-CNTRL WY

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 082152Z - 090015Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...AT LEAST ISOLATED SVR THUNDERSTORMS COULD OCCUR ACROSS
   PARTS OF THE DAKOTAS AND ADJACENT MT/WY INTO THE EVENING HOURS...AND
   CONVECTIVE TRENDS WILL BE MONITORED FOR POSSIBLE WW ISSUANCE.

   DISCUSSION...WATER VAPOR IMAGERY SUGGESTS THAT LITTLE IN THE WAY OF
   DEEP FORCING FOR ASCENT WILL BE PRESENT WITHIN A BROAD RIBBON OF
   ENHANCED MID-LEVEL MOISTURE CRESTING A CNTRL-CONUS RIDGE. ALSO...SFC
   OBSERVATIONS REVEAL LIMITED CONVERGENCE AMIDST A WEAK-FLOW PATTERN
   WITHIN A RELATIVELY MOIST -- ALBEIT NOT PARTICULARLY WARM -- AIR
   MASS LOCATED N OF A WAVY...QUASI-STATIONARY FRONT ANALYZED FROM SRN
   SD INTO THE NEB PANHANDLE AND ERN WY. THIS IS WHERE THE
   JUXTAPOSITION OF SFC DEWPOINTS IN THE LOWER/MIDDLE 60S WITH
   TEMPERATURES IN THE MIDDLE 70S TO THE LOWER 80S BENEATH MODESTLY
   STEEP MID-LEVEL LAPSE RATES IS SUPPORTING MODERATE INSTABILITY.
   ABUNDANT AREAS OF MULTI-LAYERED CLOUDS HAVE LIMITED DIABATIC SFC
   HEATING/DESTABILIZATION...AND THERE IS SUBSTANTIAL UNCERTAINTY
   REGARDING THE COVERAGE OF ROBUST CONVECTIVE DEVELOPMENT AND
   ASSOCIATED SVR POTENTIAL.

   REGARDLESS...SUFFICIENT LOW-LEVEL ASCENT COULD EXIST INVOF
   ILL-DEFINED BOUNDARIES/WIND-SHIFT AXES/TERRAIN-DRIVEN 
   CIRCULATIONS -- E.G. A WIND-SHIFT AXIS LYING FROM WRN ND TO 
   NERN WY -- FOR AT LEAST ISOLATED DEEP CONVECTION TO CONTINUE INTO
   THE EVENING HOURS. ALSO...SOME UPTICK IN CONVECTION MAY OCCUR IN
   ASSOCIATION WITH INCREASING ASCENT WITHIN THE EXIT-REGION OF A
   NOCTURNALLY STRENGTHENING LOW-LEVEL JET STREAM OVER THE LOWER PLAINS
   LATER THIS EVENING. GIVEN THE PRESENCE OF 30-50 KT OF MID-LEVEL FLOW
   PER AREA VWP DATA...DEEP SHEAR MAY BE SUFFICIENT FOR A FEW
   SUSTAINED/ORGANIZED CONVECTIVE STRUCTURES...WHICH COULD ALSO SPREAD
   E OF ONGOING WW 516. A CONDITIONAL POTENTIAL FOR SVR WIND/HAIL MAY
   OCCUR WITH SUCH ACTIVITY...THOUGH INCREASING NOCTURNAL
   BOUNDARY-LAYER CINH MAY REDUCE ANY SVR WIND THREAT WITH TIME INTO
   THE EVENING HOURS.

   ..COHEN/EDWARDS.. 09/08/2013


   ATTN...WFO...FGF...ABR...BIS...UNR...CYS...BYZ...GGW...RIW...

   LAT...LON   43820070 42850475 42830599 43450649 44740614 46630567
               47310340 48180119 47759940 45669858 43820070