1PM Day 3 Convective Outlook for Thursday, February 19. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE LOWER/MIDDLE OHIO VALLEY
SUMMARY
Severe thunderstorms with potential to produce a few tornadoes and damaging wind gusts are possible across parts of the middle Mississippi into lower Ohio Valleys Thursday afternoon into early evening.
Synopsis
Two shortwave troughs are expected to quickly lift north-northeastward through the central Plains and into the Ohio Valley region on Thursday. The initial perturbation will reach Illinois/Indiana by early afternoon. The intensity of this feature will remain modest with perhaps some gradual weakening in time. The second trough will evolve in the lower Missouri Valley during the evening and intensify as it approaches the lower Ohio Valley by Friday morning. At the surface, a cyclone will deepen as it lifts northeastward from eastern Kansas into the Great Lakes region. At least partially modified Gulf moisture will advect northward ahead of the surface cold front from the Upper Midwest into the southern Plains.
Lower/middle Ohio Valley
Ahead of the cold front, a prefrontal trough/pseudo dryline is expected to be the focus for convective development during the afternoon. The degree/quality of moisture return ahead of this feature will be key in terms of the overall magnitude of the severe threat. Current observations (Tuesday) from soundings depict a very modest moist layer along the Gulf coast. A modest shortwave trough on Tuesday night into Wednesday will lift northward too quickly for more substantial moisture return. The surface pattern on Thursday will be more robust, but deeper moisture may still not reach far enough north given that mid 60s F dewpoints are only as far north as the central Gulf currently. Guidance suggests mid to upper 50s F dewpoints are most probable, which does seem reasonable. That said, temperatures aloft will not be overly cold and lapse rates will not be overly steep. This will lead to convection that may remain somewhat low topped in nature. Despite limiting factors within the environment, 40-50 kts of effective shear roughly perpendicular to the boundary will favor discrete storms. Low-level flow will be increasing with time as well. Supercells capable of few tornadoes, damaging winds, and isolated large hail are possible during the afternoon/evening.