Mesoscale Discussion 0815
NWS Storm Prediction Center Norman OK
0319 PM CDT Thu May 21 2026
Areas affected...portions of northeastern Colorado...southeast
Wyoming and western Nebraska
Concerning...Severe potential...Watch possible
Valid 212019Z - 212215Z
Probability of Watch Issuance...60 percent
SUMMARY...Thunderstorm development is expected to continue this
afternoon with a few stronger storms possible. Supercells with a
risk for hail, damaging gusts and perhaps a brief tornado are
possible. A WW is being considered for parts of the area.
DISCUSSION...As of 2015 UTC, visible and radar imagery showed
showers and thunderstorms developing within the broad upslope flow
regime from eastern WY into northeast CO and western NE. Aided by
deep ascent from the approaching upper low over the northern Plains,
diurnal heating has been somewhat muted by lingering low clouds.
Surface dewpoints will gradually increase, with clearing and steep
lapse rates eventually supporting moderate buoyancy.
Area VADs show 40-50 kt of deep-layer shear supportive of organized
supercells. Hail is the primary risk with these storms owing to
steep lapse rates, cold mid-level temperatures and the elongated mid
and upper-level hodographs. Damaging gusts will also be possible,
especially to the west where low-level lapse rates are steeper. A
tornado or two is also possible later this evening with increasing
low-level shear and terrain influence, but this remains uncertain.
Current expectations are for storms to increase in intensity over
the next 2-3 hours but remain fairly isolated. Deepening cumulus has
been noted along the Cheyenne Ridge and the Palmer Divide. These
areas are likely to severe as the primary focus for stronger storm
development this afternoon. Father north, weaker buoyancy will
likely limit intensity, though an isolated severe threat could exist
over southeastern WY and western NE. Given the expected increase in
the severe risk with time, a WW is being considered.
..Lyons/Hart.. 05/21/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...GLD...BOU...CYS...
LAT...LON 41400261 41030229 40410211 39640206 39130230 39070277
39110357 39230431 39510463 40340475 41390494 41920469
42040397 41750281 41400261
MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
Source link