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Wednesday, August 11, 2021

SPC Aug 11, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Wed Aug 11 2021 Valid 111200Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms associated with wind damage and isolated large hail will be possible today across parts of the upper Mississippi Valley and Great Lakes region. A swath of wind damage along with potential for a couple tornadoes will be possible across parts of Lower Michigan. Marginally severe wind gusts will also be possible across parts of the central and northern Appalachians. ...Upper Mississippi Valley/Great Lakes... A broad cyclonic upper-level flow pattern will be in place today across the north-central and northeastern U.S. At the surface, a cold front will advance southeastward into the western Great Lakes region this afternoon. Ahead of the front, surface dewpoints in the lower to mid 70s F will contribute to strong instability by afternoon across a broad warm sector from the mid Missouri Valley to the central Great Lakes region. As low-level convergence becomes enhanced along the front, thunderstorm development will likely take place during the afternoon from upper Michigan southwestward into eastern Iowa. Thunderstorm development is expected to increase in coverage during the late afternoon and early evening along and ahead of the front as it moves east-southeastward across the region. An MCS could develop out of this activity during the early to mid evening in parts of the western and central Great Lakes. In addition to strong instability, model forecasts show moderate deep-layer shear today across most of Wisconsin and Lower Michigan suggesting supercell development may occur with cells that remain discrete. The current thinking is that supercell development will be most likely during the late afternoon from southern and eastern Wisconsin into southern Upper Michigan, while convection remains more widely scattered. Supercells should be capable of producing wind damage and isolated large hail. Once MCS development occurs, linear mode may become dominant and the potential for damaging wind gusts should become the greater of the two threats. Areas with more widespread damaging wind gusts will be possible across parts of northern and central Lower Michigan where instability and shear is forecast to be maximized in the early evening. An isolated tornado threat may also develop with any supercell that can remain intact within the MCS. A small Enhanced Risk has been added across parts of Lower Michigan, where the combination of instability and deep-layer shear is forecast to become maximized during the early evening. ...Central and Northern Appalachians... Upper-level flow will remain cyclonic and from the west-southeast across much of the central and northern Appalachians today. At the surface, dewpoints will remain in the upper 60s and lower 70s F across much of the Northeast today, contributing to moderate instability by afternoon. Thunderstorms are expected to form in the upper Ohio Valley during the morning with this activity moving eastward into the higher terrain during the early afternoon. Although deep-layer shear will be on the weak side, low-level lapse rates will be steep. This will aid downdraft acceleration with the stronger multicells that form during the mid to late afternoon, when instability will be maximized across the region. ..Broyles/Lyons.. 08/11/2021 Read more LIVE: spc.noaa.gov
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