2AM Day 3 Convective Outlook for Thursday, August 21. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS
SUMMARY
An isolated severe threat is expected to develop over parts of the northern Plains on Thursday, with severe gusts and hail possible.
Northern Plains
A mid-level shortwave trough is forecast to move eastward across Saskatchewan on Thursday, as a cold front advances southeastward into the northern Plains. Ahead of the front, a north-to-south axis of moderate instability is forecast by afternoon across parts of the eastern South Dakotas. During the late afternoon, scattered thunderstorms are expected to form to the east of the front, from far northwestern Minnesota into the eastern South Dakota. NAM forecast soundings near the instability axis in the late afternoon have MLCAPE peaking in the 2500 to 3500 J/kg range, with 0-6 km shear mostly in the 35 to 45 knot range. This is due to directional shear in the boundary-layer and westerly flow in the mid-levels. This could support a potential for supercells, if modes end up as discrete. Supercells would be capable of hail and isolated severe gusts. There is some uncertainty as to the location of the maximum threat, which will depend on the timing of the front and distribution of low-level moisture and instability. An upgrade in category could be necessary if the models continue to show a more favorable scenario.