1PM Day 1 Convective Outlook for Thursday, February 19. THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ILLINOIS AND SOUTHERN INDIANA
SUMMARY
Severe thunderstorms including a few tornadoes, large hail and damaging wind gusts are expected across parts of the Midwest and lower Ohio Valley today.
20Z Update
No changes to the ongoing forecast appear to be needed at this time. Dewpoints have had a tendency to mix into the upper 50s F this afternoon in the lower Ohio Valley region. Convection has thus far struggled to mature/intensify as a result. Areas of southern Illinois into southwestern Indiana should be favored for more robust storm initiation over the next few hours as the shortwave trough moves in from the west. See the previous discussion for additional details.
Midwest/Ohio Valley
Recent surface analysis places a low over eastern KS with a dryline extending southwestward from this low through central OK and into west TX. A warm front also extends eastward from this low across central MO through central IL and central IN, separating the moistening airmass south from the stable and cold airmass north. Surface observations currently show mid 50s dewpoints through southern IL and southern IN, with the 60s dewpoints farther south into western KY. This surface low is forecast to progress northeastward across central MO and into west-central IL today before continuing northeastward into the southern Lake Michigan vicinity by early tomorrow. Continued northward moisture advection is anticipated as this low progresses, but this low-level moistening will be countered somewhat by boundary-layer mixing, resulting in some uncertainty to how high the dewpoints will reach across the OH Valley this afternoon. General consensus places upper 50s dewpoints into the I-70 corridor by the late afternoon.
These increasing dewpoints coupled with cold temperatures aloft and afternoon temperatures in the upper 60s/low 70s should result in modest airmass destabilization within the warm sector, despite a relatively warm layer between 850-700 mb. In addition to improving thermodynamics, the deep-layer southwesterly flow is forecast to strengthen as well. The strongest mid-level flow will likely be displaced just south of the better thermodynamics, but forecast shear profiles are still quite robust across the OH Valley. The general expectation is for this robust vertical shear (i.e. effective bulk shear over 50 kt this afternoon) to somewhat compensate for the more modest buoyancy, resulting in an organized storm mode and supercells.
The dryline will likely remain west of this region during the afternoon, with the lift over the warm sector provided by a subtle lead shortwave currently moving through southern MO. This shortwave should interact with the warm sector across the OH Valley this afternoon, supporting thunderstorm development. Overall coverage is not expected to be high, but any storms that do mature could produce all severe hazards, including tornadoes. Additionally, the robust shear suggests that once a storm matures, it could persist for several hours. Given this updraft persistence in the presence of veering low-level wind profiles, a strong (EF2+) tornado is possible.
Additional thunderstorms are possible along the front during the evening and overnight from the TN Valley eastward into the central Appalachians. A few strong to severe storms are possible, but limited buoyancy should keep this potential isolated. Greatest probability for a severe storm along the front currently appears to be across western/middle TN and southern-central KY this evening.