12AM Day 2 Convective Outlook for Tuesday, September 2. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS INTO THE UPPER MIDWEST
SUMMARY
Isolated severe thunderstorms are possible across parts of the northern Plains into the Upper Midwest tomorrow (Tuesday).
Synopsis
Broad cyclonic mid-level flow will persist along the Eastern Seaboard while upper ridging continues west of the Rockies, with the central U.S. placed under a northwesterly upper-flow regime tomorrow (Tuesday). A large and pronounced embedded mid-level shortwave will quickly translate southeastward from Canada and overspread the Upper MS Valley through the day, encouraging a surface cold front to surge southward across the northern Plains and Upper Midwest. Thunderstorms will develop ahead of the cold front, a few of which may be severe.
Northern Plains into the Upper Midwest
Preceding the cold front will be a warm and seasonally moist airmass, overspread by 6.5-7.5 C/km mid-level lapse rates, yielding MLCAPE peaking in the 1500-2000 J/kg range by afternoon. Strengthening northwest flow with height will also yield modestly curved and elongated hodographs and 35+ kts of speed/effective bulk shear. These conditions will favor the development of multicells and perhaps a transient supercell with the stronger updrafts that manage to form ahead of the cold front. Isolated severe gusts or instances of hail are plausible, warranting the introduction of Category 1/Marginal risk severe probabilities this outlook.