SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Mon Aug 09 2021 Valid 100100Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN GREAT LAKES REGION AND IN PARTS OF THE NORTHERN PLAINS... ...SUMMARY... Severe storms are still expected this evening into tonight over parts of the northern Plains and southern Great Lakes states. Large hail and wind damage will be the primary threat in the northern Plains. Wind damage, hail will be possible across parts of northeast Illinois and northwest Indiana. ...Southern Great Lakes... A shortwave trough evident on water vapor imagery is currently located across from upper Michigan into eastern Wisconsin. At the surface, a low is located in southeast Wisconsin with a cold front extending southwestward across northern Illinois. Ahead of the front, a very moist airmass is in place, with surface dewpoints generally from the upper 60s to the mid 70s F. This is contributing to a moderately to strongly unstable airmass across much of Illinois. Strong to severe thunderstorms are ongoing just ahead of the front along the northern part of the instability axis from north-central Illinois to the Chicago Metro. The latest WSR-88D VWP from Chicago has 0-6 km shear near 40 kt with 0-3 km storm relative helicity around 400 m2/s2. This wind shear will continue to support supercells with isolated large hail and wind damage. The severe threat should continue through much of the evening as a line of strong to severe storms moves eastward into northwest Indiana and southwest Lower Michigan. ...Northern Plains... The latest water vapor imagery shows an upper-level trough over the northern High Plains with southwest mid-level flow located over much of the northern Plains. At the surface, a sharply defined cold front is moving southeastward across eastern North Dakota and central South Dakota, with surface low located in southeastern North Dakota. Instability is maximized ahead of the front across eastern South Dakota and southeastern North Dakota, with surface dewpoints generally in the upper 60s and lower 70s F. Thunderstorms are ongoing near the front and surface low where the RAP is estimating MLCAPE in the 2500 to 3500 J/kg range. This is consistent with the Aberdeen 00Z sounding which has a mid-level lapse rate near 8.5 C/km. This combined with 35 to 40 kt of 0-6 km shear will be favorable for supercells with large hail. Hailstones of greater than 2 inches in diameter may occur with the more dominant supercell updrafts. Wind damage will also be possible with supercells and with the more organized multicell line segments. The severe threat may persist through the late evening as a cluster of storms moves eastward into northwestern Minnesota. ...Central Plains... An upper-level trough is analyzed across the northern High Plains and central Rockies according to water vapor imagery. At the surface, a cold front is located in central Nebraska with dewpoints ahead of the front generally in the lower to mid 70s F. This is contributing to moderate instability across southern and central Nebraska. Thunderstorms are ongoing near the front from the vicinity of McCook northeastward to near Lexington, Nebraska. The North Platte 00Z sounding has 0-6 km shear near 25 kt with a very steep lapse rates from the surface to 500 mb. This combined with the moderate instability will support a marginal severe threat. Isolated damaging wind gusts and hail will be possible with high-based thunderstorms for a couple more hours this evening. ..Broyles.. 08/10/2021 Read more LIVE: spc.noaa.gov
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