Mesoscale Discussion 1643
Issued: · Valid: –
Summary
Damaging wind gusts, large hail, and a brief tornado may occur across parts of Upper Michigan, northern Wisconsin, and far east-central Minnesota tonight. The severe threat is expected to persist through the evening with potential wind gusts reaching 55-70 mph.
Product Text
000 ACUS11 KWNS 180002 SWOMCD SPC MCD 180002 MIZ000-WIZ000-MNZ000-180230- Mesoscale Discussion 1643 NWS Storm Prediction Center Norman OK 0702 PM CDT Fri Jul 17 2026 Areas affected...Parts of Upper Michigan...northern Wisconsin...and far east-central Minnesota Concerning...Severe potential...Watch unlikely Valid 180002Z - 180230Z Probability of Watch Issuance...20 percent SUMMARY...Severe risk will continue spreading east-southeastward into tonight. The primary concern will be damaging wind gusts. DISCUSSION...An east/west-oriented cluster of thunderstorms is tracking southeastward across far northwestern WI, generally focused along a cold front and associated surface wind shift. A deeply mixed PBL downstream may continue to promote outflow dominant storm structure, with the primary risk being locally damaging wind gusts. However, around 30-40 kt of line-orthogonal effective shear could support embedded supercell structures capable of severe gusts and isolated large hail as well. Over Upper MI, around 1500 J/kg MLCAPE and stronger deep-layer shear (around 50 kt of effective shear) will conditionally support supercell structures with any storms that spread/develop across the area tonight amid a gradually strengthening warm-advection plume. Additionally, the latest surface analysis shows a warm front draped across the area, and the MQT VWP is sampling a related clockwise-curved low-level hodograph. This boundary and related enhancement to the low-level shear/streamwise vorticity could provide a locally favorable corridor for storm organization and the potential for damaging winds, hail, and a brief tornado tonight. Current thinking is that the overall severe threat will remain too marginal and/or localized for a watch, though convective trends are being monitored -- especially over Upper MI where a locally greater severe risk is possible. ..Weinman/Hart.. 07/18/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MQT...GRB...DLH...MPX... LAT...LON 46589032 47048911 47128849 47048791 46878753 46648707 46568667 46688626 46598601 46278596 46128661 46028788 45918889 45279164 45199250 45299311 45659339 45969323 46369254 46469192 46589032 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