Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1155 AM CDT Wed Sep 20 2017 Valid 211200Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN DAKOTAS INTO THE UPPER GREAT LAKES... ...SUMMARY... Hail-producing storms are possible from the eastern Dakotas into the U.P. of Michigan Thursday night. ...Discussion... Pronounced upper trough will migrate into the Great Basin by the end of the day2 period as strongest 500mb flow translates into the central Rockies. Ahead of this feature, mid-level heights will rise across the north-central US and a lee surface cyclone should evolve over the high Plains which will shift into SD during the overnight hours. Prior to this lee cyclone development, surface front should stall across southern WI/IA region then lift north during the latter half of the period in response the approaching upper trough. The lack of large-scale forcing for ascent along this front, combined with height rises, suggest deep convection will struggle to develop much of the day. However, moisture advection in response to strengthening LLJ during the overnight hours is expected to aid destabilization atop retreating continental air mass over the upper MS Valley. Forecast soundings suggest substantial elevated instability will evolve from the eastern Dakotas into the upper Great Lakes region where MUCAPE is forecast in excess of 3000 J/kg along the cool side of the boundary. Latest guidance suggest elevated thunderstorms will evolve along a corridor from the eastern Dakotas toward Lake Superior after 06z. Large hail could be noted with this activity. At this time will maintain 5% severe probabilities due to aforementioned height rises but there is some concern that a corridor of elevated thunderstorms could evolve such that higher severe probs may be warranted after dark. ..Darrow.. 09/20/2017Read more
from SPC Forecast Products http://ift.tt/ws9HZn
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