ZCZC SPCSWOMCD ALL ACUS11 KWNS 280146 SPC MCD 280146 KYZ000-OHZ000-INZ000-ILZ000-MOZ000-280345- Mesoscale Discussion 0167 NWS Storm Prediction Center Norman OK 0746 PM CST Tue Feb 27 2024 Areas affected...southern Illinois and Indiana into portions of northern Kentucky and southwest Ohio Concerning...Severe potential...Watch likely Valid 280146Z - 280345Z Probability of Watch Issuance...95 percent SUMMARY...The severe risk is expected to increase this evening and overnight upper-level ascent and a fast-moving cold front intersect with the retreating dryline. Bowing segments and supercells will be capable of all severe hazards as they spread east along the OH Valley. A new Tornado Watch will likely be needed in the next 1-2 hours. DISCUSSION...Over the last hour, surface obs near STL showed the dryline retreating westward with a surge in dewpoints to the low 60s F. Evening water-vapor and IR imagery showed large-scale ascent beginning to impinge on the warm sector across portions of the mid MS and lower OH Valleys. Weak convection in the well-mixed warm sector to the west has steadily deepened, and should move into more robust surface moisture this evening. Additional convection also appears likely to develop along the cold front surging southeastward across eastern MO later tonight. Low 60s F surface dewpoints and ~1000 J/kg of MLCAPE will support strong updrafts within the warm sector. Very favorable deep-layer shear (50-60 kt) will support a mix of supercells and short bowing segments. Damaging gusts and hail appear likely, given the strong vertical shear and favorable buoyancy. Rapidly increasing low-level shear (evident on area VADs) may support a risk for tornadoes, especially with more sustained supercells. A significant tornado also cannot be ruled out, given very large effective helicity of 400-600 m2/s2 and a 50-60 kt 850 mb jet. Confidence remains low on the exact timing of convective initiation, given that some convective inhibition remains. As ascent begins to deepen, most hi-res guidance, and extrapolation of weaker convection farther west, suggests new storms should develop in the next 1-2 hours and quickly become severe. With all severe hazards possible, a new Tornado Watch is likely needed in the next couple of hours for parts of southern IL/ IN into northern KY and southwestern OH. ..Lyons/Edwards.. 02/28/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ILN...LMK...IND...PAH...ILX...LSX... LAT...LON 36848841 36748893 36778938 37198983 37468988 37978985 38718946 39188830 40018593 40278485 40188455 39788434 39268422 38748426 38288439 37958475 37428636 36888832 36848841 NNNN