SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1247 AM CDT Tue Aug 10 2021 Valid 101200Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with wind damage and hail will be likely in parts of the Upper Midwest this afternoon and evening. Additional storms with isolated damaging winds and hail may occur in parts of the central Plains and southern Great Lakes region. Marginally severe wind gusts will also be possible in parts of the Ohio Valley and central Appalachians. ...Upper Midwest/Great Lakes.... A broad cyclonic flow pattern will be in place today across the north-central U.S as a shortwave trough moves eastward across the upper Mississippi Valley. At the surface, a cold front will advance southeastward into the upper Mississippi and mid Missouri Valleys. Ahead of the front, a very moist airmass will be in place with surface dewpoints generally in the 70s F. As surface temperatures warm during the day, a large area of strong instability should develop from the lower Missouri Valley into the mid to upper Mississippi Valley. Although large-scale ascent should be weak across much of the warm sector, thunderstorm development may take place along pre-existing outflow boundaries and thermal gradients. Due to the strong instability and very steep low-level lapse rates, an isolated wind-damage threat will be possible with cells that can grow upscale. The greatest convective coverage is expected across parts of southern Wisconsin where model solutions develop a low-level jet during the early evening. NAM forecast soundings to the south of Madison, Wisconsin at 03Z/Wednesday have a very impressive thermodynamic environment with MLCAPE reaching 5000 to 6000 J/kg and 700-500 mb lapse rates approaching 8.5 C/km. This combined with 0-6 km shear around 25 knots should support a wind-damage threat with the stronger multicells during the late afternoon and early evening. If a cold pool can become organized, then a swath of wind-damage may occur across parts of southern Wisconsin and far northern Illinois. Wind gusts of over 70 knots will be possible along the leading edge of any line segment that can get organized during the early to mid evening. Hail will also be possible within the stronger cores of any line segment. ...Central Plains/Mid Missouri Valley... A broad cyclonic flow pattern will be place today across the north-central U.S. At the surface, a low is forecast to develop across central Kansas as moisture advection occurs across the central Plains. By afternoon, a southwest-to-northeast corridor of moderate to strong instability should be in place from Kansas into Iowa. Surface dewpoints along this corridor should be from the mid 60s to lower 70s F, resulting in MLCAPE peaking in the 3000 to 5000 J/kg range during the late afternoon. Although large-scale ascent will remain weak in the central Plains and mid Missouri Valley, thunderstorm development will be possible along pre-existing outflow boundaries as low-level convergence becomes enhanced. Very steep low to mid-level lapse rates and sufficient deep-layer shear may result in a marginal wind-damage threat during the late afternoon and early evening. ...Ohio Valley/Central Appalachians... West to southwest mid-level flow will be located across the southern Great Lakes region today. A very moist airmass will be in place over much of the southern Great Lakes region into the Ohio Valley. Moderate to strong instability is expected to develop by afternoon within the moist airmass due to warming surface temperatures. Although large-scale ascent will be weak in most areas, thunderstorm development will be possible along pre-existing outflow boundaries or along thermal gradients. Any storm that can grow upscale may be able to produce marginally severe wind gusts, mainly due to the instability and steep low-level lapse rates. ..Broyles/Lyons.. 08/10/2021 Read more LIVE: spc.noaa.gov
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