Mesoscale Discussion 0643
   NWS Storm Prediction Center Norman OK
   0207 PM CDT Wed May 20 2020

   Areas affected...eastern WY...southwest SD...the western NE
   Panhandle and portions of northeast CO

   Concerning...Severe potential...Watch likely 

   Valid 201907Z - 202030Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorms are expected to increase over the next
   couple of hours. Large hail and locally damaging wind gusts are
   possible. A watch will likely be needed by 20z.

   DISCUSSION...A surface low near the southeast MT/northeast WY
   border, east of the Big Horn mountains, was noted in 18z
   mesoanalysis. A strong baroclinic zone across the High Plains as
   allowed modest surface moisture to spread across the region on gusty
   southeasterly low level winds. Surface dewpoints are generally in
   the 50s to the east of a dryline/surface trough extending southward
   across eastern WY into eastern CO. Strong heating has allowed
   temperatures to warm into the upper 70s to low 80s beneath a plume
   of steep midlevel lapse rates of 7.5-8.5 C/km. As a result, moderate
   destabilization is occurring, with MLCAPE values increasing to
   around 1500 J/kg. 

   Recently, vertically developing CU has been noted across parts of
   southeast WY over the higher terrain of the Laramie Range, but also
   further east near the dryline/surface trough near Platte and Goshen
   Counties. Water vapor satellite loops suggest stronger ascent is now
   spreading northeast across parts of western CO/WY and convective
   initiation is likely in the next couple of hours. Initially storms
   will likely develop off the higher terrain and shift northeast in
   the vicinity of the surface trough across east-central and northeast
   WY. Additional storms are expected to develop southward later this
   afternoon/evening into portions of southeast WY/far northeast CO and
   the western NE Panhandle as a cold front overtakes the dryline and
   develops eastward as the western upper trough ejects eastward. Shear
   profiles will strengthen with time, with effective shear greater
   than 40 kt and moderately long, straight hodographs favoring cells
   capable of large hail initially. A deeply mixed boundary layer
   resulting in steep low level lapse rates will allow for strong
   downdrafts capable of locally damaging winds. Storm clusters will
   likely experience some degree of upscale growth due to outflow
   interactions and an increasing low level jet during the evening as
   convection approaches the WY/SD/NE border. While the tornado threat
   appears low, backed southeasterly low level winds will enhance
   effective SRH toward western SD/NE as storms move into a more moist
   environment. Therefore, a tornado cannot be ruled out.

   ..Leitman/Guyer.. 05/20/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LBF...UNR...BOU...CYS...BYZ...

   LAT...LON   40520434 41250536 41980561 43380564 43720562 44480543
               44780529 44890509 45010447 45060379 44780320 44480295
               43970278 43040270 41030287 40510319 40410366 40520434