SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Wed Aug 11 2021 Valid 120100Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER MISSISSIPPI VALLEY AND SOUTHERN GREAT LAKES... ...SUMMARY... Severe thunderstorms associated with wind damage, hail and an isolated tornado threat will be possible this evening across parts of the upper Mississippi Valley and southern Great Lakes region. Marginally severe storms with strong wind gusts will be possible from parts of the upper Ohio Valley into the Mid-Atlantic and Northeast. ...Upper Mississippi Valley/Great Lakes... The latest water vapor imagery shows a broad cyclonic flow pattern across the north-central states and Great Lakes region. At the surface, a cold front is advancing eastward across Wisconsin. A moist air mass is located ahead of the front from southeast Iowa into northern Illinois and southern Wisconsin and Iowa. Ahead of the front, surface dewpoints are mostly in the 70s F, which is contributing to strong instability across much of the region. Scattered thunderstorms are ongoing ahead of the front from far eastern Iowa to western Lower Michigan. This activity will continue to move eastward this evening and will likely be accompanied with a severe threat. Regional WSR-88D VWPs across the southern Great Lakes region have moderate deep-layer shear with some directional shear in the boundary layer and speed shear in the low to mid-levels. This will continue to be supportive a severe threat with a potential for wind damage and isolated large hail. Although a wind-damage threat will likely continue across parts of the south lower Michigan this evening, the severe threat coverage is expected too sparse to maintain the Enhanced Risk...see MCD 1491. ...Mid-Atlantic/Northeast/Central North Carolina... West-southwest mid-level flow is located across much of the northeastern U.S. this evening. A shortwave trough appears to be located in the central Appalachians near a north-to-south band of convection. As this band of convection moves eastward across western and central Pennsylvania this evening, a marginal wind-damage threat will be possible. A second area of convection is ongoing from eastern Virginia north-northeastward into New Jersey. This convection is located along an axis of moderate to strong instability where MLCAPE is estimated in the 2500 to 3500 J/kg range according to the RAP. Although deep-layer shear is weak along this corridor, low-level lapse rates are steep. This will continue to be favorable for isolated strong wind gusts for a few more hours this evening. ...Central Plains... The latest water vapor imagery shows a broad plume of mid-level moisture located from the southern Rockies into parts of the southern and central Plains. At the surface, a southwest-to-northeast oriented trough is located across Kansas and northwest Missouri. Isolated to scattered thunderstorms are ongoing near the surface trough, with the greatest coverage in southwest Kansas. Surface dewpoints south of the trough are generally in the 60s F, which is contributing to moderate instability. This combined with steep lapse rates in the boundary layer will continue to support a marginal wind-damage threat for a few more hours this evening. ..Broyles.. 08/12/2021 Read more LIVE: spc.noaa.gov
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