12AM Day 2 Convective Outlook for Wednesday, July 16. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF EASTERN IOWA NORTHERN ILLINOIS AND SOUTHERN WISCONSIN
SUMMARY
Scattered strong to severe thunderstorms are possible Wednesday afternoon and evening from parts of the central High Plains to the Great Lakes.
Mid-MS Valley/Great Lakes Vicinity
An upper shortwave trough and MCV is forecast to be located over IA Wednesday morning. Some ongoing convection is possible from MN into IA associated with this feature and attendant outflow. As the MCV shifts east/northeast, a composite outflow/surface cold front located from central WI into eastern IA will develop eastward across portion of northern MO/IL through the evening. The downstream warm sector will be characterized rich moisture, with dewpoints in the 70s F. Daytime heating and modest lapse rates will support strong instability (2000-3000 J/kg MLCAPE). Vertical shear should increase as strengthening midlevel westerlies overspread the region, resulting in 25-35 kt effective shear magnitudes. Organized cells and clusters will pose a risk for damaging gusts. Low-level shear may be somewhat enhanced close to the MCV/surface low across northern IL. Forecast soundings show modestly enlarged/curved hodographs and a tornado or two could also occur. A more marginal severe risk could spread east into portions of Lower MI and northern IN during the late evening/overnight hours, but overall risk should gradually diminish with eastward extent.
Central Plains Vicinity
The western edge of a southward sagging cold front will move across eastern CO/NE and portions of KS during the day. A very moist and unstable airmass is expected across the region. Vertical shear will remain modest, with stronger midlevel westerlies expected to lag behind the front. Nevertheless, the sagging surface front should provide focus for isolated to scattered thunderstorm development within the warm sector, with an accompanying risk for strong gusts.
Additional storms are expected to develop over the central High Plains of southeast WY/eastern CO in the post-frontal upslope regime. This activity will spread eastward during the evening and may be elevated. Isolated hail and strong gusts will be possible initially. While guidance varies considerably, some potential exists for an MCS to develop over parts of KS during the nighttime hours as the front continues to sag southward and a modest low-level jet develops. Given large model spread, will hold off on higher outlook probabilities at this time.
Upper Ohio Valley
Scattered to numerous thunderstorms are expected across the region i response to a shortwave impulse. While modest instability is forecast amid a very moist airmass, vertical shear will remain weak. Sporadic strong gusts/wet microbursts could occur, but organized severe potential continues to be limited/uncertain.