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Mesoscale Discussion 661
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   MESOSCALE DISCUSSION 0661
   NWS STORM PREDICTION CENTER NORMAN OK
   0648 PM CDT FRI MAY 20 2016

   AREAS AFFECTED...NERN WY...SWRN SD...FAR NWRN NEB...FAR SERN MT

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 202348Z - 210115Z

   PROBABILITY OF WATCH ISSUANCE...5 PERCENT

   SUMMARY...AN ISOLATED HAIL THREAT WILL EXIST FOR THE NEXT 1-2 HRS
   ACROSS PARTS OF THE NRN HIGH PLAINS INTO THE BLACK HILLS OF SD...BUT
   COVERAGE WILL REMAIN SPARSE ENOUGH TO PRECLUDE WW ISSUANCE.

   DISCUSSION...A PAIR OF SLOW-MOVING STORMS /DISPLAYING OCCASIONAL
   SUPERCELL STRUCTURES/ OVER THE BLACK HILLS HAVE EXHIBITED THE
   POTENTIAL FOR SVR HAIL OVER THE PAST 1-2 HRS...WITH A RECENT REPORT
   OF 1.5 INCH HAIL RECEIVED FROM THE SRN-MOST STORM. ADDITIONAL
   CONVECTION WAS DEVELOPING WITHIN A BROADER DIFFLUENT UPPER FLOW
   PATTERN ACROSS THE HIGH PLAINS OF ERN WY. AN OUTFLOW BOUNDARY HAS
   BECOME POSITIONED ALONG THE WRN SLOPES OF THE BLACK HILLS...WHILE
   QUASI-STATIONARY FRONTAL SEGMENT EXTENDS FARTHER EWD...NOTED BY MORE
   RECENT BACKING OF SFC WINDS NEAR/N OF I-90. 

   STRONG DIURNAL HEATING FROM EARLIER TODAY HAS YIELDED MLCAPE VALUES
   OF OVER 1000 J/KG...DESPITE THE PRESENCE OF MARGINAL MOISTURE WITHIN
   THE BOUNDARY LAYER /40S TO LOW 50S F DEWPOINTS/. VWP DATA FROM UDX
   SUGGESTS LOW-MIDLEVEL FLOW IS NOT PARTICULARLY STRONG...BUT ENHANCED
   VEERING IN THE LOW LEVELS AMIDST ELY WINDS N OF THE QUASI-STATIONARY
   FRONTAL SEGMENT WILL CONTINUE TO PROVIDE SUFFICIENT DEEP-LAYER SHEAR
   FOR MARGINAL SUPERCELL STRUCTURES OVER THE BLACK HILLS. THE PRESENCE
   OF COLD TEMPERATURES ALOFT AND STEEP MIDLEVEL LAPSE RATES...COMBINED
   WITH DEEP VEERING WIND PROFILES...WILL CONTINUE TO SUPPORT ISOLATED
   SVR HAIL POTENTIAL.

   ..ROGERS/EDWARDS.. 05/20/2016


   ATTN...WFO...UNR...CYS...BYZ...

   LAT...LON   44830311 44110220 43530205 43040295 42580419 42750512
               43390597 44200577 44900571 45120508 45090373 44830311 

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Page last modified: May 21, 2016
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