Mesoscale Discussion 1689
NWS Storm Prediction Center Norman OK
1215 PM CDT Tue Jul 21 2026
Areas affected...portions of the lower and middle Ohio River Valley
Concerning...Severe potential...Watch likely
Valid 211715Z - 211845Z
Probability of Watch Issuance...80 percent
SUMMARY...Numerous strong to severe thunderstorms are expected to
form along a cold front this afternoon before progressing
southeastward. Damaging to severe wind gusts will be the primary
threat, with brief tornadoes and isolated large hail also possible.
DISCUSSION...Latest surface analysis places a cold front extending
southwestward from southern Lower Michigan into central Indiana,
southern Illinois, and south-central Missouri. A deepening cumulus
field is noted along and ahead of this cold front, with temperatures
approaching the low-90s F and dewpoints near 80. Observational
trends and latest high-res guidance suggest that robust convective
initiation will occur across this region over the next 1-2 hours.
Strong mid-level flow overspreading the region (~40 kts sampled
around 3 km AGL by the LVX/VWX VAD profiles) and strong effective
shear of 50+ kts will support initial supercells, but linear forcing
along the front, widespread initiation, and cold pool conglomeration
will promote rapid upscale growth into one or more linear
segments/clusters. Damaging/severe wind gusts to around 70 mph are
expected to be the most common hazard, but brief tornadoes and large
hail to around golf ball size are also possible.
Confidence is higher in greater storm coverage occurring from
southern Indiana into northern Kentucky, with more uncertainty
surrounding coverage existing farther west (where effective shear is
also forecast to be modestly weaker). Given the expected severe
risk, watch issuance is likely for at least a portion of the
discussion area early this afternoon.
..Chalmers/Mosier.. 07/21/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LMK...OHX...IND...PAH...ILX...MEG...
LAT...LON 36608692 36168805 35948908 35938997 36029029 36189042
36539042 37049025 37638953 38468788 38698738 38918669
39008617 39008586 38908553 38628524 38308505 37958492
37568500 37228527 36968589 36608692
MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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