12AM Day 2 Convective Outlook for Wednesday, August 27. NO SEVERE THUNDERSTORM AREAS FORECAST
SUMMARY
The potential for severe storms appears to be low across the continental U.S. tomorrow (Wednesday). A few stronger storms are possible across parts of the Upper Midwest and Colorado Front Range.
Synopsis
Broad upper troughing will persist across the eastern U.S., with an embedded impulse ejecting into the Atlantic as a second impulse impinges on the Great Lakes. An upper ridge will persist over the Southwest while a weak mid-level cut-off low meanders across the Pacific Northwest. A surface high will become established east of the MS River, with low-level moisture poised to pivot around the surface high and advect northward across the Plains into the Great Lakes region, with scattered thunderstorms expected. Scattered thunderstorms will also be possible across portions of the High Plains during the afternoon given lee surface troughing, with elevated thunderstorms continuing into the central Plains overnight within a warm-air advection regime. The best chance for any strong storms would be over portions of the Colorado Front Range and the Upper Midwest, where an overlap of marginally favorable shear and instability may exist.
Parts of the Upper Midwest
The second impulse pivoting around the broader upper trough over the Great Lakes will promote an organized round of thunderstorms within a deep-layer northwesterly flow regime. Modest mid-level lapse rates will overspread low 60s F dewpoints, resulting in up to 1200 J/kg of thin MLCAPE across extreme eastern SD toward the MN/IA border. Modest veering flow with height will encourage 25-35 kts of effective bulk shear as well. As such, a few strong storms with sub-severe wind and hail are possible around afternoon peak heating.
Colorado Front Range
Upslope low-level flow across the central High Plains will support 60+ f surface dewpoints to advect northwestward toward the Colorado Front Range. Here, increasing westerly flow with height will support some speed shear, evident in forecast soundings as relatively straight hodographs. Lapse rates are expected to be poor (i.e. around 6.5 C/km), with MLCAPE peaking around 1000 J/kg via thin profiles. A few of the stronger storms may produce some wind and hail, but these hazards are currently expected to remain generally below severe limits.