Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
934 ACUS02 KWNS 181732 SWODY2 SPC AC 181730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Wed Sep 18 2024 Valid 191200Z - 201200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE UPPER MIDWEST... ...SUMMARY... Scattered severe thunderstorms are possible from mid-afternoon to mid-evening on Thursday across central/eastern Minnesota, Iowa, and western Wisconsin. A few tornadoes, isolated very large hail, and damaging winds may occur. ...Upper Midwest... A seasonably strong stacked cyclone initially near the ND/SK/MB border region is forecast to move northeastward through the period. An attendant cold front will move eastward through the day across parts of the upper Midwest and central Plains. Diurnal heating of a rather moist airmass along/east of the front will support a relatively narrow zone of moderate to large MLCAPE (1500-3000 J/kg) by peak heating. Moderate midlevel flow will support sufficient effective shear for storm organization, with shear vectors generally aligned perpendicular to the front. This will support supercell potential from central/eastern MN into western WI and parts of IA, though the timing of initial development and western extent of the primary severe threat remain somewhat uncertain. Favorable instability and an initially discrete storm mode will support large to very large hail as storms mature, along with some potential for isolated damaging wind. Low-level hodographs will also be sufficiently curved/enlarged to support a tornado threat. A tendency toward clustering and perhaps some modest upscale growth is possible later in the storm evolution, with a severe threat likely persisting into the early/mid evening. The threat should begin to wane by late evening into Thursday night, as instability weakens with time and eastward extent. ...Eastern KS/northern OK into southeast NE/western MO... A conditionally favorable storm environment is also expected to develop from southeast NE into eastern KS/western MO and northern OK, along/ahead of the approaching front. While storm coverage will generally be less compared to areas farther north (due to weaker large-scale ascent), isolated supercells and/or stronger clusters will be possible from late afternoon into the evening. Increasingly warm midlevel temperatures will tend to limit updraft intensity with southward extent, but an isolated severe threat could extend as far south as northern OK. ..Dean.. 09/18/2024 $$