Mesoscale Discussion 1919
NWS Storm Prediction Center Norman OK
0413 AM CDT Tue Aug 11 2026
Areas affected...much of northern and central Iowa
Concerning...Severe potential...Watch possible
Valid 110913Z - 111115Z
Probability of Watch Issuance...40 percent
SUMMARY...Developing thunderstorms may continue to evolve into a
better organized cluster through 6-8 AM CDT. Eventually, this
probably will become accompanied by increasing potential for strong
to severe surface gusts, though how soon remains uncertain.
DISCUSSION...Convection continues to increase and intensify within a
zone of stronger warm advection, along a tightening
lower/mid-tropospheric baroclinic zone where seasonably high
moisture content is supporting large CAPE, beneath the northern
periphery of a plume of elevated mixed-layer air. Strongest storms,
now focused south of Sioux Falls SD into the Storm Lake IA vicinity,
have yet to organize or generate a notable surface pressure
perturbation. However, this may begin to change over the next few
hours.
While there is considerable spread within convection-allowing
guidance, of perhaps particular note, the latest Rapid Refresh
output suggests that continuing intensifying thunderstorm
development may become accompanied by the evolution of a
strengthening lower/mid-tropospheric cyclonic circulation, based on
its depiction of strengthening rear inflow to 50-60+ kt in the
700-500 mb layer through 11-13Z. This would probably be accompanied
by increasing potential for strong to severe surface gusts at some
point, though how soon remains unclear given the initially stable
near-surface lapse rates.
..Kerr/Smith.. 08/11/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DVN...ARX...DMX...FSD...
LAT...LON 43489513 43369280 42739114 41469157 41929321 42189496
42819608 43489513
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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