SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0700 AM CST Sun Dec 28 2025 Valid 281300Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN ILLINOIS TO INDIANA... ...SUMMARY... Scattered severe thunderstorms are possible over Illinois and Indiana this afternoon through the evening. Severe wind gusts capable of wind damage and a couple of tornadoes are the primary threats. ...Mid MS Valley east through IN-OH-western PA... Water-vapor imagery this morning shows a mid-level low near the MT/ND border with a trough into the central Rockies/Sangre de Cristos. This mid-level low will move into the central Great Lakes by early Monday morning. Strong southwesterly 500-mb flow (80 kt) extending from the base of the trough through the lower MO Valley and OH Valley will feature an intensifying 110-kt jet reaching the MO-IL border this evening before further strengthening to 130 kt over OH by the end of the period. A surface low over eastern KS will deepen rapidly through tonight as it moves to Lake Huron. A frontal zone extending east-northeast through the southern Great Lakes this morning will serve as the northern edge of the moist sector. A cold front initially over KS-OK will surge south-east. Southerly low-level flow across the moist sector will maintain a fetch of seasonably high 58-62 deg F dewpoints immediately ahead of the front/low. A rain shield with embedded thunderstorms this morning from northern MO into the southern Great Lakes could feature a stronger storm or two through midday, but the primary severe risk will likely focus this afternoon through tonight. Model guidance indicates the cap will erode near the evolving triple point and cold front by mid-late afternoon. Upwards of 500-1000 J/kg MLCAPE is possible across parts of central into eastern IL with buoyancy tapering with east extent across the OH Valley. A southward-developing convective band is forecast to evolve late this afternoon through the early evening. Long hodographs and strong 2-3 km flow will favor a risk for severe gusts with the more intense storms and surges with the maturing band. Models indicate the wind-damage threat may persist across the OH Valley/southern Great Lakes tonight despite meager instability. The tornado risk appears highest with cells that can develop near the instability axis and mature before either destructive interference of the larger-scale cold pool overwhelms cellular mode, and/or this activity moves farther east into lessening instability. ..Smith/Weinman.. 12/28/2025
