SPC Sep 14, 2017 0730 UTC Day 3 Severe Thunderstorm Outlook

By Newsroom America Feeds at 14 Sep 2017

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0235 AM CDT Thu Sep 14 2017 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PORTIONS OF IOWA AND MINNESOTA TO WESTERN PARTS OF THE UPPER GREAT LAKES... ...SUMMARY... A few strong to severe storms will be possible across Iowa through the upper Mississippi Valley and western extent of the Upper Great Lakes region, mainly Saturday afternoon into Saturday night. ...Synopsis... A large-scale trough developing across the Intermountain West and Rockies during Day 2 is expected to be progressive during Day 3, tracking to the northeast through the northern Plains to central Canada and northern MN by 12Z Sunday. An upper ridge will prevail across Texas and expand northeastward into the lower OH/TN Valleys. At the surface, a cold front will advance east and south through the upper MS Valley, lower MO Valley, while the southern extent reaches northern OK to the TX Panhandle by 12Z Sunday. ...IA/MN and western portions of the Upper Great Lakes... Showers and thunderstorms should be ongoing across a large part of this region at the start of Day 3. Models suggest the greatest potential for surface heating into Saturday afternoon across the Marginal risk area should be from southeast MN through IA. Stronger forcing for ascent and stronger mid- to upper-level winds/shear are expected to lag the cold front this forecast period. However, modest effective shear (25-30 kt) and moderate instability across much of the Marginal risk area (aside from northeast MN) should prove favorable for a few strong to severe storms by late afternoon. Storms that develop toward 16/22Z to 17/00Z may become undercut quickly as the cold front advances to the east across the upper MS Valley. Strong to isolated severe storms should remain possible with eastward extent across the Marginal risk area Saturday evening as thunderstorm coverage increases, though eventual weakening of instability by late evening should support a diminishing severe threat. ..Peters.. 09/14/2017 Read more



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