Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0356 AM CDT Fri Sep 10 2021 Valid 131200Z - 181200Z ...DISCUSSION... An upper trough is forecast to develop eastward across the northern and central Plains on Day 4/Monday. A surface cold front should likewise move southeastward across these regions through the day. The degree of low-level moisture return ahead of the front remains uncertain, but some potential for severe storms may exist across parts of the northern/central Plains. Medium-range guidance is in reasonably good agreement that the upper trough will amplify on Day 5/Tuesday as it continues eastward across Canada and the Midwest/Great Lakes. The surface cold front should continue southeastward on Tuesday across the central Plains, mid MS Valley, and Great Lakes regions. Enough low-level moisture and related instability may develop by Tuesday afternoon to support an isolated severe threat in a relatively narrow corridor across these areas. By Day 6/Wednesday, the primary upper trough is forecast to eject east-northeastward across Quebec/Ontario and the Northeast. There are some differences in the placement of synoptic-scale features, such as the surface cold front, at this extended time frame. Still, if current forecast trends hold, a continued severe threat may exist ahead of the cold front across parts of the Northeast and Mid-Atlantic. For Day 4/Monday through Day 6/Wednesday, too much uncertainty remains regarding sufficient low-level moisture return and the degree of instability available for surface-based storms to include any 15% severe areas. Read more LIVE: spc.noaa.gov
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