Mesoscale Discussion 1647
Issued: · Valid: –
Summary
Severe thunderstorms capable of producing large hail and damaging winds are expected to intensify across southern Michigan, northern Indiana, northwest Ohio, and northeast Illinois through this afternoon. The threat includes potential supercells and organized storm clusters that may bring wind gusts up to 70 mph and hail up to 1.25 inches.
Product Text
000 ACUS11 KWNS 181638 SWOMCD SPC MCD 181637 OHZ000-MIZ000-INZ000-ILZ000-181830- Mesoscale Discussion 1647 NWS Storm Prediction Center Norman OK 1137 AM CDT Sat Jul 18 2026 Areas affected...Southern Michigan into northeast Illinois...northern Indiana...and northwest Ohio Concerning...Severe potential...Watch possible Valid 181637Z - 181830Z Probability of Watch Issuance...60 percent SUMMARY...Thunderstorms developing along a cold front will continue to intensify and pose a risk for large hail and severe winds through the afternoon across portions of the Great Lakes/Midwest. Watch issuance is being considered and may be needed within the hour. DISCUSSION...Latest radar mosaics and GOES imagery shows maturing convection along and just ahead of a southeastward moving cold front with a few deeper, more robust updrafts noted across eastern lower MI and southwest lower MI. Downstream of this developing convection, temperatures continue to warm into the 80s within a moist air mass. With further diurnal heating expected through late afternoon, MLCIN will continue to erode as MLCAPE increases into the 2500-3000 J/kg range. Additionally, regional VWPs are sampling 35-40 knot mid-level flow over MI/OH with decreasing winds with westward extent. This flow should remain in place through the day as a mid-level wave continues to progress east/southeast towards the lower Great Lakes. Given these convective and environmental trends, the expectation is for additional thunderstorm development through the next few hours with a steady uptick in intensification. Sufficient deep-layer shear will promote organized storm modes, including the potential for a few supercells initially (especially across MI) before frontal ascent promotes increased clustering through late afternoon. Consequently, some hail threat will likely materialize before damaging/severe winds become the predominant threat through time across IN and OH. Convective trends are being monitored, and watch issuance will is probable as thunderstorm coverage continues to increase. ..Moore/Thompson.. 07/18/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...CLE...ILN...DTX...IWX...GRR...IND...LOT...ILX... LAT...LON 40098729 40398838 40788880 41218885 41608871 41788841 41898744 42108638 42438516 42748447 43278358 43518288 43448249 43248225 42738223 41768210 41038228 40438264 40088349 40098729 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN