11AM Day 2 Convective Outlook for Thursday, February 19. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY AND LOWER OHIO VALLEY
SUMMARY
Severe thunderstorms, with potential to produce a few tornadoes, hail and damaging wind gusts, are possible across parts of the middle Mississippi into lower Ohio Valleys Thursday afternoon into early evening.
Synopsis
A progressive mid-level flow regime, characterized by multiple low-amplitudes perturbations and strong west/southwesterly flow aloft is expected over the CONUS Day2/Thursday. The primary shortwave trough will move from the southern Rockies/Plains into the Midwest by 00z, assuming a slight negative tilt as multiple weaker preceding subtropical perturbation are absorbed. Strong ascent associated with the trough a 100+ kt mid-level jet streak will deepen a surface low over the eastern Plains, reaching the Great Lakes by early Friday.
Middle Mississippi and Lower Ohio Valley
As the upper trough and surface low approach the Mid MS Valley early Thursday, rapid low-level moistening is expected across parts of eastern MO western IL and the lower OH Valley. While moisture content is seasonably limited (surface dewpoints in the 50s to near 60 F), cooling mid-level temperatures ahead of the preceding subtropical shortwave trough will support some destabilization Thursday afternoon.
While instability will remain modest owing to limited boundary-layer moisture, clearing ahead of a surging dryline tied to the surface low will allow for diurnal heating. In combination with steepening mid-level lapse rates, around 500-1000 J/kg of MLCAPE is exacted by early afternoon. An arc of mainly cellular convection should develop by mid afternoon across far eastern MO and western to south-central IL and move quickly eastward. Amid very strong kinematic fields (EBWD 55+ kt) a supercell mode is expected. Strong low-level shear and the concentration of buoyancy in the lowest few km will favor strong vertical accelerations and stretching with seasonably cool mid-level temperatures. Hail is likely with the stronger rotating storms. Additionally, with backed low-level flow near the low/warm front and large low-level shear, (0-1 km BWD 25+ kt) a few tornadoes are possible.
As ascent spreads eastward, thunderstorm activity may eventually grow upscale enough to support increasing potential for damaging wind gusts given the strong background flow. However, decreasing buoyancy and weakening height falls with eastward extent should gradually limit convective intensity into parts of the middle OH Valley late Thursday evening.