SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0222 AM CDT Tue Sep 14 2021 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS AND UPPER MIDWEST... ...SUMMARY... Isolated severe storms may occur Thursday across parts of the northern Plains and Upper Midwest. ...Northern Plains into the Upper Midwest... A large-scale upper trough/low should move eastward across central Canada on Thursday, with the southern portion of this trough grazing the north-central CONUS through the period. A surface cold front is forecast to advance east-southeastward across the northern Plains and Upper Midwest through Thursday evening. Some low-level moisture return is likely ahead of this front, and diurnal heating of this airmass should foster weak to moderate instability across the warm sector by Thursday afternoon. Rather strong low/mid-level flow and related deep-layer shear associated with the upper trough is also forecast to be in place across this region, which will likely support storm organization. At least isolated storms should form along/ahead of the front by Thursday afternoon, and subsequently move eastward. Any storms that do form would pose a threat for all severe hazards, as supercells appear possible. However, the main uncertainty precluding higher severe probabilities for now is concern about storm coverage. The best lift associated with the upper trough will likely remain displaced to the north in Canada, with either neutral or very modest 12 hour 500 mb height falls forecast across the north-central states. ...Southeast... The remnant of tropical cyclone Nicholas should be located in the vicinity of southern LA at the start of the period Thursday morning per latest NHC advisory. The surface low is forecast by most guidance to be quite weak by this time, with the low-level wind field expected to further diminish through the day. At this point, any severe potential associated with this system appears too low to include severe probabilities on Thursday. ..Gleason.. 09/14/2021
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