SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Wed Aug 14 2024 Valid 141200Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTERED OVER THE MIDDLE MISSOURI VALLEY AREA... ...SUMMARY... Isolated severe thunderstorms are expected today from parts of the Intermountain West eastward across the northern and central Plains. A more concentrated risk -- including potential for large hail and damaging winds, and possibly a tornado -- is expected across the mid Missouri Valley area. ...Synopsis... A low-amplitude mid-level trough is forecast to move out of the Intermountain West and into the northern/central Plains today, shunting the central U.S. ridge eastward across the Mississippi Valley and into the Great Lakes/Ohio and Tennessee Valleys. Farther downstream, an eastern U.S. trough will gradually shift off the East Coast and into the western Atlantic. Meanwhile upstream, an eastern Pacific short-wave trough will move into the Pacific Northwest/northern California through the second half of the period. At the surface, weak/broad low pressure initially over the High Plains is forecast to gradually consolidate as it shifts eastward across the central Plains, in tandem with the advance of the upper trough. As this occurs, a cool front will shift southeastward across the central Plains through the afternoon and evening. Overnight, further consolidation of the surface low is expected as it moves slowly northeastward into southern Minnesota, while the trailing front sharpens, extending from the low southwestward across Kansas and into New Mexico by the end of the period. ...Middle Missouri Valley area... As an ongoing MCS crosses the Mid Missouri Valley area of eastern Nebraska and vicinity early in the period, a resulting/remnant outflow boundary is forecast to persist into the afternoon across the southeastern Nebraska/northwestern Missouri/southwestern Iowa area. As a moist low-level airmass undergoes diurnal heating, moderate destabilization is forecast near and south of this boundary. As low pressure -- and the attendant cold front -- shifts eastward into this area, the low/front and remnant outflow should all provide low-level foci for late afternoon storm initiation. With enhanced southerly low-level flow ahead of the advancing mid-level trough beneath moderate (30 to 40 kt) mid-level westerlies, resulting shear suggests that initial storms will likely be supercells, capable of producing large hail and damaging winds, and possibly a tornado. With time, clustering/upscale growth is expected, with guidance suggesting that an at least loosely organized band of storms should move eastward through the evening across, northwestern Missouri, and eastern Kansas. Risk for locally damaging wind gusts and some hail will likely accompany this activity, before severe risk diminishes gradually overnight. ...Wyoming and vicinity eastward across the northern and central Plains... As the upper trough -- comprised of several vorticity maxima embedded in the broader cyclonic flow field -- shifts across the Rockies toward/into the Plains, daytime heating beneath cooler air at mid levels will support modest destabilization across a broad area. Ascent -- focused near favored higher terrain areas and near various weak surface boundaries -- will contribute to widely scattered thunderstorm development during the afternoon. Moderate mid-level westerlies will contribute to shear sufficient for a few stronger storms -- and attendant risks for hail and locally strong/severe wind gusts into the evening hours. ..Goss/Halbert.. 08/14/2024
