SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1237 AM CDT Thu Aug 26 2021 Valid 261200Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR SOUTHERN MINNESOTA INTO NORTHERN IOWA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR A LARGE PART OF EASTERN MONTANA... ...SUMMARY... Severe thunderstorms capable of damaging wind gusts are likely across parts of southern Minnesota into Iowa. Severe thunderstorms will also be possible during the late afternoon and evening across parts of the northern High Plains. ...NE/SD eastward into parts of the Upper Midwest... A cluster of thunderstorms will likely be ongoing across the northern Great Plains early this morning north of a surface front. Uncertainty is still relatively high regarding the evolution of the morning thunderstorm activity subsequently transitioning to surface-based storms, as the storms move east along the surface boundary into parts of MN and northern IA during the day. Although the convective details are unclear, it seems likely the boundary will focus storm activity during the day and potentially later during the night. An initial risk for isolated severe gusts will likely increase during the day and become more concentrated across southern MN into northern IA. Further west, redevelopment will be possible during the afternoon/evening across portions of SD/NE, near and north of the surface boundary. Wherever the boundary sets up by afternoon, diurnal heating and relatively steep midlevel lapse rates should support moderate buoyancy, while seasonably strong deep-layer flow/shear ahead of the deepening upper trough will support the potential for organized cells and/or clusters. The strongest storms may remain somewhat elevated north of the surface boundary, with a threat of large hail (with initial more discrete development) and damaging wind (especially as upscale growth occurs over time). This activity is expected to spread eastward during the evening into the overnight, posing a renewed strong/locally severe thunderstorm threat into portions of the Upper Midwest. ...Montana... Post-frontal east-southeasterly flow will support a modest increase in low-level moisture on across central/eastern MT. Relatively cool midlevel temperatures associated with the deepening upper trough will support weak to locally moderate buoyancy. Model guidance continues to show widely scattered thunderstorms developing by late afternoon as an embedded disturbance approaches the area. Strongly veering wind profiles will support long, straight hodographs and effective shear of 30-40 kt, sufficient for organized cells/clusters capable of hail and severe gusts with the more intense downdrafts. ...New England... A moisture-rich airmass will be in place today ahead of a mid-level trough over eastern Canada and an associated cold front. Ample heating will result in moderate buoyancy by midday over Maine, where the southern fringe of large-scale ascent is forecast to overspread. The latest model guidance indicates only isolated storm coverage but a conditional risk for severe may accompany the stronger/sustained cores. This activity will likely diminish by early evening as a cold front sweeps through northern New England late. ..Smith/Moore.. 08/26/2021 Read more LIVE: spc.noaa.gov
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