SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1257 AM CDT Mon Aug 23 2021 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Isolated severe thunderstorms are possible across parts of the central and northern Plains from this afternoon into the overnight period. ...Central and Northern Plains/Upper Mississippi Valley... Southwest mid-level flow will be in place today across the central and northern Plains. Heights will rise across the northern Plains today as a shortwave trough exits the region to the east. At the surface, a low will deepen across eastern Montana as southeasterly winds strengthen in much of the Dakotas. A moist airmass will be in place from southeastern South Dakota and northeastern Nebraska eastward into southern Minnesota and Iowa. Moderate to strong instability will develop along this corridor by afternoon. Although large-scale ascent will be weak, low-level convergence will increase during the mid to late afternoon. This will aid isolated convective development. RAP forecast soundings by late afternoon from near Sioux Falls eastward across southern Minnesota show MLCAPE in the 3000 to 3500 J/kg range with 0-6 km shear near 30 kt. This environment may support supercell development. Any supercell could be associated with a hail and isolated wind damage. However, if linear mode is favored, then the wind-damage threat would be greater. The severe threat is conditional due to spatial uncertainty. Further to the west in the central and northern High Plains, convection will likely initiate in the higher terrain of southeast Wyoming this afternoon. This convection is forecast to move across the High Plains this evening. As low-level flow strengthens across the Dakotas this evening into tonight, moisture advection will take place. In response, a northwest-to-southeast corridor of moderate instability should develop from central South Dakota into southwest North Dakota by late evening. Thunderstorms that move across this corridor of instability may obtain a severe threat. Forecast soundings around midnight from Mobridge to Bismarck have a sharp inversion below 850 mb but also have effective shear near 40 kt and steep mid-level lapse rates. This could be enough for a hail threat with elevated supercells. The elevated severe threat may develop northeastward with time as convection moves across the northern Plains tonight. ..Broyles/Jirak.. 08/23/2021 Read more LIVE: spc.noaa.gov
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