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Tuesday, August 10, 2021

SPC Aug 11, 2021 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 PM CDT Tue Aug 10 2021 Valid 110100Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR SOUTHEAST WISCONSIN AND NORTHEAST ILLINOIS... ...SUMMARY... Severe thunderstorms capable of wind damage and isolated large hail will be possible this evening across parts of the Upper Midwest and Great Lakes. Marginally severe winds will also be possible from parts of the central Plains into the Ohio Valley, with a few strong gusts also possible across the Mid-Atlantic. ...Upper Midwest/Great Lakes... A shortwave trough is evident on water-vapor imagery from near the Arrowhead of Minnesota extending southward into far eastern Iowa. An MCS is ongoing ahead of the shortwave trough from far eastern Wisconsin into northeast Illinois. The MCS is located along an axis of strong instability, analyzed by the RAP just to the west of Lake Michigan, where MLCAPE is estimated in the 3500 to 5000 J/kg range. Concerning the wind shear, the WSR-88D VWP at Milwaukee and Chicago both have 0-6 km shear near 20 kt with most of the speed shear with the lowest one kilometer above ground level. This combined with very steep low-level lapse rates will be favorable for damaging wind gusts along the leading edge of the stronger multicells. Isolated large hail could also occur. The wind-damage threat should be greatest over the next hour before the line of storms moves over Lake Michigan. A severe threat is expected to continue this evening as the MCS moves into southern Lower Michigan and northwestern Indiana but should be more isolated due to weaker instability in those areas...see MCD 1468 and WW 421. ...Central Plains... A pattern with broad cyclonic mid-level flow is currently located across the north-central U.S. At the surface, a trough of low pressure is analyzed from the Oklahoma Panhandle northeastward into Iowa along which moderate to strong instability is present. Isolated thunderstorms have developed early this evening along the instability axis where low-level convergence is enhanced, from far eastern Colorado into central Kansas. The RAP has MLCAPE maximized across north-central Kansas where MLCAPE is estimated to be near 4000 J/kg. This combined with 20 to 30 kt of deep-layer shear and very steep low-level lapse rates should be favorable for a marginal wind-damage threat. Hail could also occur with the stronger updrafts. The severe threat may persist for a couple more hours before instability weakens substantially across the region. ...Mid-Atlantic... The latest surface analysis shows an ill-defined trough from central Pennsylvania southward into the Carolinas. A very moist airmass is located to the east of the trough with surface dewpoints in the lower to mid 70s F. An axis of moderate instability is analyzed to the east of the surface trough where isolated strong thunderstorms are ongoing. MLCAPE in the 1000 to 2000 J/kg range along with steep low-level lapse rates may be enough for a few marginally severe gusts early this evening. ..Broyles.. 08/11/2021 Read more LIVE: spc.noaa.gov