There has been a lot of talk about an upcoming severe weather outbreak tomorrow, Friday, March 2, 2012 and for good reason.
A large upper-level trough, currently over the western US, will continue to progress eastward tonight and deepen as it does so. At the surface, an area of low pressure will develop across the southern Plains in response to this trough. This will will then move northeastward late tonight and tomorrow, deepening while it does so. The cold front that brought tornadoes to several states yesterday, will begin to move back northward as a warm front tonight, bringing warm, moist air with it. By tomorrow evening this warm front will be as far north as Lake Erie.
The surface low will track from central Oklahoma to Lake Huron by tomorrow night. An associated cold front will progress eastward through the Ohio, Tennessee, and Mississippi Valleys, igniting severe storms.
Storms will first fire across far eastern Oklahoma, southern Missouri, and Arkansas after midnight tonight. These storms will be elevated and will have ample elevated CAPE to work with, on the order of 750-1500 J/Kg. For most of tonight these storms will mainly pose a large hail threat, however, whenever the storms become surface based (likely sometime tomorrow morning) the tornado and damaging wind threat will drastically increase. Storms will fire farther eastward along the northward moving warm front as well late tonight. The same holds true with these storms.
As we head into tomorrow morning, additional storms will likely fire across southern Illinois/far western Kentucky. These storms will then progress east northeastward across southern Indiana/northern Kentucky. By noon these storms will likely be nearing southwestern Ohio.
Dewpoints across this area will be in the upper 50s to lower 60s with CAPE on the order of 1000-1750 J/Kg. A potent shortwave trough will be moving across northern/central Missouri at this time, providing extra support for the storms. In general, the farther east across this area, the better the directional wind shear, and the better the chance for tornadoes. Any storm that gets rooted to the warm front will likely have the best shot at producing a tornado, possibly strong and possibly long lived.
As you head southward into Tennessee, Mississippi, and Alabama storms will fire ahead of the cold front around dusk or just after dark. The main threat with these storms will be damaging winds and hail. An isolated tornado cannot be ruled out. This line of storms will move eastward through this area overnight, likely producing a large swath of wind damage as the storms become linear.
Storms will likely fire across northern and central Indiana during the late afternoon. Additional storms will fire across western Ohio during the evening hours. These storms will move eastward through Ohio and will likely become severe, at least for a time. The directional wind shear across northeast Ohio is amazing (see Fig. 1), but the limited moisture and instability across the area will tend to drastically lower the tornado threat. Nonetheless, a few tornadoes are possible across this portion of Ohio along with damaging wind gusts in excess of 65 mph and hail to the size of golfballs. As the storms move into western Pennsylvania at night, the severe threat will begin to wane.
A few storms will fire during the daytime across portions of the Carolinas and may produce small hail and wind gusts to 55 mph.
A potential limiting factor across much of the western Tennessee Valley will be morning convection and cloud cover. I believe there is a high likelihood that the clouds will break up allowing for ample daytime heating, but if not this could inhibit storm development and severity across this area.
Below is my outlook for severe weather for tomorrow. I expect widespread severe storms within the red shaded areas. Storms here have the potential for isolated tornadoes, damaging wind gusts in excess of 70 mph, and large hail. I went with a Threat Level Black, meaning I expect a tornado outbreak across this area. I consider a tornado outbreak to consist of at least 20 confirmed tornadoes with at least 2 being of EF-3 intensity or stronger. The greatest threat in this area will be during the afternoon and evening.