Mesoscale Discussion 1211
NWS Storm Prediction Center Norman OK
0150 PM CDT Sat Jun 20 2026
Areas affected...Wyoming
Concerning...Severe potential...Watch possible
Valid 201850Z - 202045Z
Probability of Watch Issuance...40 percent
SUMMARY...High-based thunderstorms capable of severe downburst winds
will spread across central and northeast Wyoming through the
afternoon. Trends are being monitored for the need for a watch
issuance, though thunderstorm coverage remains uncertain.
DISCUSSION...Over the past 1-2 hours, relatively shallow, but
high-based, convection has begun spreading across western WY with a
second region of storms more recently developing within the Wyoming
Basin/southern WY. Across both regions, clearing skies ahead of the
developing storms has allowed surface temperatures to warm into the
70s with dewpoints mixing into the mid to upper 30s. Based on recent
forecast guidance, these surface conditions suggest that the
boundary-layer has now fully mixed to around 3 to 3.5 km deep with
around 250-500 J/kg of MLCAPE. Although buoyancy is fairly meager,
the combination of a deeply mixed boundary layer and 30-35 knots of
effective shear should promote persistent convection capable of
producing strong to severe downburst winds. Latest CAM guidance
continues to depict this threat well and suggests swaths of 50-75
mph winds may emerge across central to northeast WY through the
early evening hours.
The primary uncertainty in the short-term forecast is the lingering
cloud cover further downstream across central/northeast WY, which is
muting diurnal heating (temperatures remain in the 60s) and limiting
boundary-layer depth. Although this cloud cover is rapidly
progressing northeast, it is unclear if the window of mostly clear
skies will be sufficient to produce a deeply-mixed boundary layer
conducive for severe winds. Consequently, confidence in the severe
wind threat is greatest in the near-term, but some severe wind
threat may materialize further downstream through the evening if
sufficient heating can occur. Convective trends are being monitored,
and watch issuance may be needed.
..Moore/Hart.. 06/20/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...UNR...CYS...BYZ...RIW...
LAT...LON 41590803 41560864 41810917 42790999 43380985 43820942
44730731 44770647 44650585 44370528 44010471 43560421
43280411 43290414 42950408 42050407 41540430 41260460
41160491 41210540 41490579 41700619 41790658 41750715
41590803
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
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