SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1059 AM CDT Wed Mar 19 2025 Valid 191630Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF CENTRAL/NORTHERN ILLINOIS AND WEST CENTRAL INDIANA... ...SUMMARY... Scattered severe thunderstorms are possible this afternoon/evening from central/northern Illinois to western Indiana. A few tornadoes, large hail, and damaging wind gusts will be possible. ...IL/IN vicinity into early tonight... A deep (990mb) surface low over northwest MO this morning will continue to shift east into northern IL through late afternoon, and into IN/MI and southern Ontario overnight. Meanwhile, the exit region of a 90-100+ kt 500 mb jet will overspread IL/IN this afternoon into early evening. Cloud cover and elevated convection this morning across IA and northern IL, along with lofted dust moving over the region may inhibit heating to some degree into the afternoon. Furthermore, boundary layer moisture is expected to remain modest, most likely in the 51-54 F range given 15z upstream observations in the low 50s F. If any stronger heating occurs, mixing may further limit dewpoints from climbing into the mid/upper 50s F as suggested by some forecast guidance. Nevertheless, cold temperatures aloft (-17 C on 12z RAOBs from DVN) will support steep midlevel lapse rates and modest destabilization into the early afternoon. A dryline is noted across central MO at 15z. This feature will continue to sweep east into the afternoon and become a focus for stronger thunderstorm development across IL by 18-19z. Vertical shear will be favorable for supercells given elongated hodographs with enlarged, looping low-level hodographs. These vertical wind profiles are already evident in VWP data from DVN and LOT where a west to east oriented surface warm front is roughly aligned across east-central IA/northern IL. Evolution of modest boundary layer moisture will be key for determining the tornado risk this afternoon across IL/IN. If dewpoints can reach 55-56 F, a localized area of enhanced tornado potential may develop. While some risk for tornadoes will still exist with lower dewpoints, the risk would be more muted and likely less intense. Given the conditional risk for a strong tornado or two, will maintain the 10 percent SIG tornado risk. Otherwise, somewhat low-topped supercells will also pose a risk for damaging gusts of 60-70 mph and isolated large hail up to 1-1.5 inches in diameter. Isolated convection may develop southward along the dryline/cold front into western/central KY by late afternoon before convection weakens after sunset. ...TN/MS/AL vicinity this afternoon/evening... Dewpoints have gradually increased into the mid 50s late this morning. Continued warm advection ahead of a wind shift this afternoon should allow dewpoints to reach the upper 50s to low 60s F. While forcing for ascent will be weak compared to further north, it should be sufficient to erode capping in the persistent warm advection regime. Instability will remain modest, generally near/less than 500 J/kg MLCAPE. While vertical shear will be quite strong, this should limit updraft intensity/longevity. A broken band of storms may still pose a risk for a few strong gusts. ..Leitman/Bunting.. 03/19/2025