Mesoscale Discussion 1358
NWS Storm Prediction Center Norman OK
0712 PM CDT Mon Jul 26 2021
Areas affected...Northeast MN into northwest WI
Concerning...Severe Thunderstorm Watch 393...
Valid 270012Z - 270145Z
The severe weather threat for Severe Thunderstorm Watch 393
SUMMARY...The threat for very large hail and locally damaging wind
continues with ongoing supercell cluster across northeast MN. This
cluster will likely spread into northwest WI, where new watch
issuance is likely by 01Z.
DISCUSSION...At 00Z, an intense thunderstorm cluster with embedded
supercells is ongoing across northeast MN. The strongest cell within
this cluster earlier produced baseball-size hail, damaging wind, and
a tornado across northern MN. MLCAPE in excess of 1500 J/kg and
effective shear of 40-50 kt will continue to support supercell
structures as the cluster spreads southeastward, with renewed
development possible along the southwestern flank as the low-level
jet gradually increases this evening.
Some uncertainty remains regarding whether this cluster will evolve
into a forward propagating MCS, or persist as a supercell cluster.
In either case, a significant hail and wind threat is expected to
spread into northwest WI this evening, with a tornado or two also
possible if the supercell mode is maintained. A new severe
thunderstorm watch will likely be issued for northwest WI by 01Z.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 47239444 47549316 47529205 47349131 47139072 46369045
45779022 45809189 45839353 46159444 47229464 47239444