12AM Day 2 Convective Outlook for Friday, June 27. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN PLAINS
SUMMARY
Severe storms producing large hail and locally damaging winds are forecast over parts of the northern Plains Friday afternoon and evening. Sporadic damaging gusts may also occur over parts of the Mid Atlantic and Southeast.
Synopsis
A low amplitude trough will move across the northern Rockies and into the northern Plains on Friday, with 40+ kt 500 mb winds into the Dakotas. As this occurs, a surface trough will develop over the western Dakotas, providing a focus for thunderstorms during the day. To the east, a weaker wave will move from lower MI into the lower Great Lakes, with a surface low enhancing convergence/lift. The air mass will remain moist and unstable over much of the central and eastern CONUS, supporting scattered storms over much of the area. The strongest instability is expected over the northern Plains in advance of the upper system. Otherwise, a weak upper low will remain over GA/FL providing cool midlevel temperatures and aiding daytime storm development.
Northern Plains
Strong heating will lead to an uncapped air mass within the surface trough, with scattered areas of storms developing from northeast CO into western NE and from the western into the central Dakotas. Supercells are most likely across the Dakotas beneath the stronger flow aloft, with the strongest cells producing very large hail and perhaps a brief tornado. Farther south across NE, CO and KS, deep mixed layers should favor strong outflow and localized wind damage. Storms may increase again during the evening over eastern ND and northern MN with increasing southwest flow at 850 mb late.
Southeast and Mid Atlantic
A weak surface trough will develop from VA across the Carolinas and into GA with strong heating. A moist and unstable air mass will again favor areas of thunderstorms beneath the upper ridge. Lapse rates aloft and therefore total instability will not be as strong as previous days, but widely scattered strong to damaging gusts may still occur during the afternoon across the entire region.