Strong to severe thunderstorms are possible across portions of South Dakota and Nebraska into southern Minnesota and Iowa. Additional strong to severe storms may occur across portions of West Virginia, Virginia and North Carolina.
Stronger mid/upper level westerly flow will remain confined to thenorthern tier of the U.S. from the northern Plains to New England.Shortwave impulses will migrate through the westerly flow, butstronger instability will remain displaced to the south of the beltof stronger flow. Nevertheless, a weak surface low and attendanttrough is forecast to develop over the northern/central High Plains,and a stalled front will gradually lift north across the northernPlains and portions of the Midwest. Rich boundary layer moisture anda plume of steep midlevel lapse rates will support strongdestabilization across parts of KS/NE/SD and the Mid-MO Valley.
Vertically veering wind profiles will support rotating storms, whileelongated/straight hodographs above 2-3 km appear favorable forhail. Steep low-level lapse rates, and some modest dry air notedbetween 700-500 mb suggest damaging wind potential is also possible.While some modest low-level hodograph curvature is noted, 0-1 kmshear is expected to remain modest, though a tornado or two cannotbe ruled out.
While this environment generally appears favorable for at leastisolated supercells, convective evolution is uncertain givensomewhat subtle forcing. Additionally, forecast height tendenciesare neutral to possibly small height rises as a shortwave upperridge builds over the MT/WY after 21z. Capping across portions ofthe region could limit coverage. Where capping is not an issue,strong instability and modest shear could result in rapidclustering. Furthermore, early convection may be ongoing acrossparts of ND/SD into MN. How these storms and associated cloudinessevolve through the morning, and any potential outflow generated bythis convection also result in uncertainty. Given theseuncertainties, despite a favorable airmass, will maintain Marginal(level 1 of 5) probabilities with some expansion of the area.Outlook upgrades may be necessary later if some of theaforementioned uncertainties are resolved.
A weak shortwave impulse is forecast to migrate across the BlueRidge to the Mid-Atlantic coast in modest westerly flow on thenorthern periphery of the upper high. A very moist airmass willsupport moderate destabilization. While shear will remain modest,multicell clusters could produce strong downbursts. If storms canorganize along consolidating outflows, increasing potential fordamaging winds will occur.