SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 1154 AM CST Sat Dec 27 2025 Valid 281200Z - 291200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON AND EVENING ACROSS PARTS OF EAST CENTRAL AND SOUTHEAST MISSOURI...ADJACENT NORTHEASTERN ARKANSAS AND NORTHWESTERN TENNESSEE...CENTRAL AND SOUTHERN ILLINOIS...INDIANA...WESTERN OHIO AND ADJACENT SOUTHERN LOWER MICHIGAN...WESTERN AND NORTHERN KENTUCKY... CORRECTED FOR TYPOS ...SUMMARY... Strong thunderstorms may develop across parts of the middle Mississippi Valley Sunday afternoon, accompanied by at least some risk for severe weather while spreading into the lower Ohio Valley through Sunday evening. This may include potential for a tornado or two across parts of central Illinois into north central Indiana. Otherwise, potentially damaging wind gusts appear the primary severe threat. ...Discussion... Much of the interior U.S. remains anomalously warm, as westerlies across the Pacific into western North America undergo amplification. Later today through Sunday, models indicate that this will include mid/upper ridging building inland across British Columbia and the Pacific Northwest, through the Canadian/northern U.S. Rockies and adjacent Prairies/northern Great Plains. Downstream, it appears that a pair of short wave troughs will come in phase while migrating across and east of the Rockies, and provide support for strong cyclogenesis. By late Sunday night, guidance generally indicates that the center of a deep, occluding surface low will reach the Lake Huron/Georgian Bay vicinity, with a strong trailing cold front advancing through the western slopes of the Appalachians and northwestern Gulf/Gulf coast region. ...Middle Mississippi/Ohio Valley... There remains notable spread within/among the various model output concerning the evolution of the developing surface cyclone across the lower Missouri Valley through Great Lakes region, including timing of periods of more rapid deepening Sunday through Sunday night. This could substantially impact the location, timing and extent of any associated thunderstorm development and accompanying severe weather potential. In general, it does appear that the pre-frontal warm sector will be relatively moist, with surface dew points near/above 60F likely as far north as a developing warm front, east of the deepening surface low, across parts of middle Mississippi Valley into southern Great Lakes region by Sunday afternoon. Convection allowing guidance and other model output suggest that forcing for ascent along the warm front, near and east of the low, may be the focus for highest thunderstorm probabilities through the period. However, based on forecast soundings, relatively warm mid-level temperatures will tend to minimize CAPE, and the risk for severe hail and wind with convection rooted above the cool/stable boundary layer appears negligible. Relatively warm air aloft appears likely to be problematic within the surface warm sector as well, particularly given forecast weaker mid/upper forcing for ascent. However, there does appear a consensus in model output that a corridor of weak pre-cold frontal boundary-layer destabilization could develop by early Sunday afternoon across parts of south central/east central Missouri into central Illinois. Coincident with strengthening deep-layer wind fields/shear and perhaps a period of glancing mid/upper support for upward vertical motion, there may be a window of opportunity for strong thunderstorm development, which could spread just ahead of the front into the Ohio Valley before diminishing Sunday evening. Based on forecast soundings, low-level hodographs to the east-southeast of the deepening cyclone may become conducive to low-topped supercells posing the risk for a tornado or two across parts of central Illinois into north central Indiana late Sunday afternoon. Otherwise, low-level hodographs, trending more linear along the cold front to the southwest, will generally support a narrow line of convection with potential mix down 40-50 kt mean flow in the lowest 3 to 6 km. Once thunderstorm development wanes, the potential for convectively enhanced gusts will diminish, but strong wind gusts associated with the cold frontal passage are likely through much of the remainder of the Ohio and Mississippi Valleys. ..Kerr.. 12/27/2025
