2AM Day 3 Convective Outlook for Saturday, June 28. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL NEBRASKA AND EASTERN SOUTH DAKOTA INTO MINNESOTA AND WESTERN WISCONSIN
SUMMARY
Scattered severe storms with wind and hail potential will be possible over parts of the northern Plains to upper Mississippi Valley Saturday afternoon and evening.
Synopsis and Discussion
Shortwave ridging will occur over the upper MS Valley during the day on Saturday, before height falls arrive in association with a low-amplitude upper trough moving across MT and the Dakotas. This will allow a large area of moisture and instability to build, with MUCAPE over 4000 J/kg forecast from the eastern Dakotas into MN and IA.
A surface trough is forecast to deepen from the eastern Dakotas into central NE, as southerly winds maintain a northward flux of theta-e with a deepening moist boundary layer. The end result should be storms developing within this trough, which will then spread east and persist through evening.
While shear will not be particularly strong, steep midlevel lapse rates combined with veering winds with height will favor initial robust cells capable of large hail and perhaps a brief tornado risk, before storms form into propagating clusters with damaging winds likely. The surging theta-e out of the southwest during the evening may allow severe storms to persist into western WI late.
Elsewhere, widespread moisture and instability will remain over the Southeast and Mid Atlantic, with scattered clusters of afternoon storms likely. Pockets of stronger instability may support localized strong to damaging gusts. Predictability is currently too low to denote precisely which areas may see a low-end severe gust threat.