Day 1 Convective Outlook
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Summary
Severe thunderstorms capable of producing damaging wind gusts and occasional large hail are possible across portions of Iowa and eastern Nebraska on Tuesday afternoon and evening.
Product Text
000 ACUS01 KWNS 080539 SWODY1 SPC AC 080538 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CDT Tue Sep 08 2026 Valid 081200Z - 091200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF IOWA AND EASTERN NEBRASKA... ...SUMMARY... Widely scattered severe storms capable of mainly severe wind gusts appear possible across portions of Iowa and eastern Nebraska Tuesday afternoon and evening. More sporadic occurrences of severe winds and large hail may occur from portions of the upper Midwest into the central Plains. ...Synopsis... An intense upper low moving into southern SK late this evening will continue northeast through central MB into northern ON ahead of a secondary short-wave trough tracking from the northern Rockies into the northern Plains. A belt of enhanced mid/upper-level winds will be maintained between those features from the northern High Plains into the upper Great Lakes. At the surface, a cold front will advance through the eastern Dakotas and upper MS Valley with the trailing extension of the boundary moving more slowly southeast through the mid-MO Valley and central High Plains. ...Central Plains into the upper Midwest... Clusters of thunderstorms are likely to be ongoing at 12Z Tuesday from portions of the mid-MO Valley into the upper Midwest within a zone of warm advection and moisture transport along a nocturnal low-level jet (LLJ). Showers and storms may linger through the morning across parts of WI and the U.P. of MI, limiting the degree of air mass destabilization and associated severe weather risk during the afternoon. Farther to the southwest from IA through eastern and southern NE into northern KS, stronger daytime heating on the southern fringe of lingering mid/high-level cloudiness will contribute to a well-mixed boundary layer, featuring steep low-level lapse rates. When combined with boundary-layer dewpoints in the 60s to low/mid 70s F, the air mass is expected to become moderately to strongly unstable by late afternoon with MLCAPE of 2000-3000 J/kg. In the absence of appreciable height falls/large-scale forcing for ascent, convergence along the front and any preceding confluence zones/outflow boundaries is expected to foster a gradual increase in storm coverage and intensity by mid to late afternoon amidst the destabilizing air mass. The strongest deep-layer shear is expected to be displaced to the north of the effective warm sector with around 30-35 kt forecast along the frontal zone. A largely parallel shear-vector orientation with the front suggests that initial storms should grow upscale into line segments or a broken band with an associated risk for severe wind gusts from mid afternoon through evening. Isolated occurrences of marginally severe hail are possible; however, poor mid-level lapse are expected to limit the overall threat. The 00Z models do indicate some LLJ enhancement over central IA by late afternoon into evening, resulting in a corridor of stronger low-level shear. While a brief tornado or two are possible, a more robust threat is expected to be limited by largely outflow-dominant storms. ..Mead/Chalmers.. 09/08/2026 $$