Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 22 2025 06:01:34 ACUS01 KWNS 220601 SWODY1 SPC AC 220600 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sun Jun 22 2025 Valid 221200Z - 231200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE GREAT PLAINS...UPPER MISSISSIPPI VALLEY AND NORTHEAST... ....SUMMARY... Isolated to scattered thunderstorms are expected to develop today across the northern Plains and Upper Mississippi Valley, some of which could have large hail, damaging wind gusts and an isolated tornado threat. Storms associated with severe gusts and hail may also develop across parts of the Northeast, and in the southern and central Plains. ....Great Plains/Upper Mississippi Valley... At mid-levels, southwest flow will be in place today across the Great Plains, as a trough moves into the northern Rockies. At the surface, a cold front will advance southeastward across the northern Plains, as a low moves from the eastern Dakotas into northwest Minnesota. The boundary will be the focus for convective development. To the east of the front, a very moist airmass will be in place with surface dewpoints in the upper 60s to mid 70s F from the central Plains northeastward into upper Mississippi Valley. Moderate to strong instability is forecast to develop across much of the region this afternoon. This, coupled with moderate deep-layer shear, will be favorable for severe thunderstorm development. Thunderstorms are expected to first develop across parts of North Dakota and northwest Minnesota this morning. This activity could be associated with large hail and isolated severe gusts. As surface temperatures warm and low-level convergence increases near the boundary early this afternoon, scattered storms are expected to develop across parts of the central and northern Plains. These storms will gradually grow upscale into a organized convective cluster, moving through eastern South Dakota and western Minnesota. RAP forecast soundings near Sioux Falls, SD at 21Z have MLCAPE in the 3000 to 3500 J/kg range with 25 to 30 knots of 0-6 km shear. In addition, 700-500 mb lapse rates are forecast to be near 9 C/km. This should be favorable for supercells and/or intense multicells capable of producing large hail and wind damage. Supercells that track through the more unstable air to the east of the front could produce hailstones greater than 2 inches in diameter, and have an isolated tornado threat. If an intense line segment can organize, then severe gusts above 70 mph will be possible as well. Further south-southwest into parts of the southern and central High Plains, scattered thunderstorms are expected to develop this afternoon and evening. Surface dewpoints in the 60s F will contribute to moderate instability. This, combined with very steep lapse rates from the surface to 700 mb, will likely support a marginal severe threat. Hail and a few severe gusts will be the primary threats. ....Northeast... A line or cluster of thunderstorms will likely be ongoing across the Northeast at the start of the period. The outflow boundary associated with this convection is expected to move south and southwestward into the central Appalachians of Pennsylvania and New York this morning. Moisture advection will result in a steady increase in surface dewpoints across much of the region today, with surface dewpoints increasing into the lower 70s F. As surface temperatures warm, an axis of strong destabilization is expected to take shape around midday. Thunderstorms that can develop near the boundary will move southeastward along the axis of strong instability. RAP forecast soundings from 18Z to 21Z near the boundary have MLCAPE around 3000 J/kg range, with 700-500 mb lapse rates of 7 C/km and moderate deep-layer shear. This should support a threat for large hail and damaging wind gusts during the afternoon. ...Broyles/Moore.. 06/22/2025 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .