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Mesoscale Discussion 1556
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   MESOSCALE DISCUSSION 1556
   NWS STORM PREDICTION CENTER NORMAN OK
   0632 PM CDT MON JUL 27 2015

   AREAS AFFECTED...PORTIONS OF ERN MT...WRN SD...NERN WY

   CONCERNING...SEVERE THUNDERSTORM WATCH 456...

   VALID 272332Z - 280130Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 456
   CONTINUES.

   SUMMARY...THE RISK FOR SVR TSTMS CONTINUES ACROSS WW 456.

   DISCUSSION...WATER VAPOR LOOPS SUGGEST THAT THE SPATIAL GAP BETWEEN
   STRONG DCVA PRECEDING A BECOMING-NEGATIVELY-TILTED MID-LEVEL
   SHORTWAVE TROUGH OVER WRN/CNTRL MT AND MODERATELY TO STRONGLY
   UNSTABLE AIR SAMPLED OVER ERN MT INTO THE WRN DAKOTAS AND NERN WY IS
   CLOSING. A CORRESPONDING UPSWING IN THE NUMBER AND INTENSITY OF
   TSTMS IS ONGOING BASED ON THE LATEST VISIBLE SATELLITE AND MOSAIC
   RADAR IMAGERY...AND THIS WILL CONTINUE AS THERMODYNAMIC PROFILES
   ALOFT COOL WITH FORCED ASCENT DRIVING ADIABATIC COOLING. CONVECTION
   WILL LIKELY BECOME SCATTERED TO NUMEROUS ACROSS THE WATCH AREA IN
   THE NEXT FEW HOURS...WITH A MIX OF BOWING SEGMENTS AND OCCASIONAL
   SUPERCELLS AFFECTING THE AREA.

   THE GGW VWP SAMPLES 40-50 KT OF MERIDIONAL FLOW IN THE 4-6-KM-AGL
   LAYER OFFERING STRONG DEEP SHEAR FOR ORGANIZED CONVECTION. SVR WIND
   GUSTS AND LARGE HAIL WILL BE LIKELY...AND SIGNIFICANTLY SVR
   WIND/HAIL CANNOT BE RULED OUT OWING TO THE STEEP-LAPSE-RATE PROFILE
   IN PLACE. AREAS OF GREATEST CONCERN INCLUDE THE ERN ONE-THIRD OF MT.
   THIS IS WHERE BUOYANCY IS MOST SUBSTANTIAL...AND A TIGHTENING
   CROSS-FRONTAL ISALLOBARIC COMPONENT IS OCCURRING ACROSS A
   FRONTOGENETIC COLD FRONT ADVANCING EWD OVER CNTRL MT. A TORNADO
   CANNOT BE RULED OUT WITH ANY MORE DISCRETE SUPERCELL STRUCTURES IN
   ERN MT...PARTICULARLY IN PROXIMITY TO...AND ON THE COOL SIDE OF A
   COLD-FRONT-PRECEDING...WAVY...QUASISTATIONARY BOUNDARY ANALYZED FROM
   NERN MT TO THE BIG HORN MOUNTAINS. THIS IS WHERE STRONG DIRECTIONAL
   SHEAR IN THE LOW LEVELS IS ENHANCING SRH TO AROUND 150-200 M2/S2 IN
   THE 0-1-KM-AGL LAYER BASED ON THE GGW VWP. HOWEVER...POTENTIAL MODE
   TRANSITIONS TO QUASI-LINEAR COMBINED WITH THE OVERTAKING
   FRONTOGENETIC BOUNDARY MAY LIMIT THE SVR RISK.

   MORE ISOLATED SVR CONVECTION CONTINUES IN A PRESENTLY
   WEAKER-FORCING-FOR-ASCENT REGIME INTO WRN SD...WHERE SUPERCELL
   STRUCTURES HAVE BEEN NOTED. SUCH ACTIVITY WILL LIKELY CONTINUE IN
   THE SHORT TERM WITH SVR HAIL/WIND POTENTIAL...AND AN UPSWING IN
   CONVECTIVE COVERAGE MAY OCCUR IN THE NEXT FEW HOURS AS MID-LEVEL
   HEIGHT FALLS CONTINUE TO OVERSPREAD THE AREA.

   ..COHEN.. 07/27/2015


   ATTN...WFO...UNR...BYZ...GGW...

   LAT...LON   45740377 45630247 44910151 43930138 43430155 43260220
               43260294 43630387 44100478 44520568 44860648 45570741
               46780783 47790805 48340795 48730730 48660633 47400517
               46140444 45740377 

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