Mesoscale Discussion 1918
NWS Storm Prediction Center Norman OK
0115 AM CDT Tue Aug 11 2026
Areas affected...parts of southeastern South Dakota...southwestern
Minnesota...northeastern Iowa
Concerning...Severe potential...Watch possible
Valid 110615Z - 110815Z
Probability of Watch Issuance...40 percent
SUMMARY...Increasing thunderstorm development posing mainly a risk
for scattered, occasional large hail appears possible through 3-4 AM
CDT. It remains unclear when/if this may require a severe weather
watch, but trends will be monitored for more substantive upscale
growth and organization, which may be accompanied by increasing
potential for strong to severe gusts toward daybreak.
DISCUSSION...To the south/southeast of a low-amplitude digging short
wave trough, latest Rapid Refresh output suggests that warm
advection in the 850-700 mb layer will gradually become focused in
corridor roughly east of Pierre SD into the Spencer IA vicinity
through 08-09Z. Isolated intensifying thunderstorm development is
already underway within this regime to the southwest of Sioux Falls,
and a further increase during the next few hours appears possible,
though this is not depicted particularly well by convection allowing
guidance.
Beneath steep mid-level lapse rates, inflow of moist air supportive
of large CAPE on the order of 2000-3000+ J/kg may support elevated
supercells capable of producing large hail, in the presence of
strong cloud-bearing layer shear. This appears likely to be rooted
above a relatively deep saturated surface-based layer with generally
weak to stable lapse rates. So, while localized downbursts might
still be possible, the potential for damaging surface gusts may be
generally slow to evolve, and await substantive consolidation and
upscale growth.
..Kerr/Smith.. 08/11/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FSD...OAX...ABR...
LAT...LON 44429876 44509705 43719488 42759509 42659616 42809723
43179796 43659893 44429876
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
Source link