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Mesoscale Discussion 1641
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   MESOSCALE DISCUSSION 1641
   NWS STORM PREDICTION CENTER NORMAN OK
   0649 PM CDT SAT AUG 30 2014

   AREAS AFFECTED...SERN MT...SWRN ND...WRN SD

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 302349Z - 310115Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...AT LEAST A SMALL WINDOW OF OPPORTUNITY STILL APPEARS TO
   EXIST FOR SEVERE STORM DEVELOPMENT INCLUDING ISOLATED SUPERCELLS
   THROUGH THE 01-03Z TIME FRAME.  IT REMAINS UNCERTAIN WHETHER A
   SEVERE WEATHER WATCH IS NEEDED...BUT TRENDS CONTINUE TO BE MONITORED
   FOR THIS POSSIBILITY.

   DISCUSSION...LATEST OBSERVATIONAL DATA AND RAPID REFRESH OUTPUT
   SUGGEST THAT THE ENVIRONMENT HAS BECOME INCREASINGLY SUPPORTIVE OF
   SUPERCELL DEVELOPMENT ACROSS THE REGION DURING THE PAST COUPLE OF
   HOURS... NORTH THROUGH EAST OF A DEVELOPING SURFACE LOW NEAR THE
   BLACK HILLS.  BOUNDARY LAYER MOISTENING IN A NARROW CORRIDOR EAST
   THROUGH NORTH OF THE BLACK HILLS APPEARS TO BE CONTRIBUTING TO
   SIZABLE MIXED LAYER CAPE IN EXCESS OF 2000 J/KG...BENEATH MODEST
   SOUTHWESTERLY MID-LEVEL FLOW WHICH MAY CONTINUE TO STRENGTHEN TO
   AROUND 40 KT OR SO DURING THE NEXT FEW HOURS.

   SCATTERED THUNDERSTORM ACTIVITY HAS BEEN INCREASING TO THE WEST...
   ACROSS EASTERN WYOMING INTO THE BLACK HILLS AREA...AND NEW
   DEVELOPMENT STILL SEEMS LIKELY ACROSS PARTS OF SOUTHEASTERN
   MONTANA...NORTHWESTERN SOUTH DAKOTA...AND SOUTHWESTERN NORTH
   DAKOTA...IN RESPONSE TO INCREASING LARGE-SCALE FORCING FOR UPWARD
   VERTICAL MOTION.  THIS WILL BE ASSOCIATED WITH LOW-LEVEL WARM
   ADVECTION ON THE NOSE OF A STRENGTHENING LOW-LEVEL JET /30-50 KT AT
   850 MB/...AND AN AREA OF MID/UPPER FORCING NOW SPREADING ACROSS THE
   EASTERN MONTANA/WYOMING BORDER TOWARD THE CENTRAL DAKOTAS.

   BEFORE THE UNSTABLE BOUNDARY LAYER BEGINS TO STABILIZE WITH THE LOSS
   OF DAYTIME HEATING...A WINDOW OF OPPORTUNITY STILL APPEARS FOR
   SEVERE STORM DEVELOPMENT...INCLUDING A COUPLE OF SUPERCELLS. 
   UPSCALE CONVECTIVE GROWTH INTO A CONSOLIDATING/GROWING CONVECTIVE
   CLUSTER PROBABLY WILL OCCUR THIS EVENING...BUT THE EXTENT OF ANY
   CONTINUING SEVERE THREAT REMAINS UNCLEAR WITH ACTIVITY SEEMING
   LIKELY TO BECOME INCREASINGLY ROOTED ABOVE A COOLER/MORE STABLE
   BOUNDARY LAYER AS IT SPREADS NORTHEASTWARD INTO/THROUGH THE CENTRAL
   DAKOTAS.

   ..KERR/EDWARDS.. 08/30/2014


   ATTN...WFO...BIS...LBF...UNR...BYZ...

   LAT...LON   45740481 46520416 47080353 46310278 45610210 44120129
               42980263 44130348 44470392 44950510 45740481 

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Page last modified: August 31, 2014
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