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Mesoscale Discussion 0895 NWS Storm Prediction Center Norman OK 0844 AM CDT Wed Jun 10 2020 Areas affected...northern IN...southwest and western Lower MI Concerning...Severe potential...Severe Thunderstorm Watch likely Valid 101344Z - 101515Z Probability of Watch Issuance...80 percent SUMMARY...Storms will gradually intensify this morning and likely require a severe thunderstorm watch issuance by 11am-12pm EDT. Max thunderstorm gust potential will initially range 45-60 mph but strengthen into the 50-70 mph range towards midday as both the magnitude/coverage of damaging gusts increases. DISCUSSION...Radar mosaic shows a developing band of storms from east-central IL to the Chicago south side with another cluster of storms developing over northwest IN expected to move into southwest Lower MI during the next 1-2 hours. Visible-satellite imagery shows cloud streets across northern IN into southern Lower MI, indicative of a very moist boundary layer. Specifically regarding moisture, the 6am EDT Detroit, MI observed sounding showed a 16.3 g/kg lowest 100mb mean mixing ratio, a climatological maximum through June 15th during the period of record (since 1949). Pockets of strong heating per cloud breaks will contribute to a moderately unstable airmass by mid-late morning with little to any remaining convective inhibition as temperatures warm into the low-mid 80s. KIWX and KGRR show 30-40 kt in the 1-2 km AGL layer with 50 kt around 3km AGL at KGRR. As the mid-level migratory shortwave trough approaches the Great Lakes from MO today, additional storm development/strengthening is expected. As a result, damaging gusts will become more common as bands of storms intensify through the late morning and into the early afternoon. A tornado or two cannot be ruled out given the moist boundary layer and adequate speed shear in the lowest 1-2 km, but the general unidirectional southerly wind profile will tend to favor damaging gusts as the primary severe hazard.
