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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Thursday, May 20, 2021

SPC May 20, 2021 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1236 AM CDT Thu May 20 2021 Valid 211200Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL TO NORTHERN HIGH PLAINS AND UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with hail and strong gusty winds will be possible Friday in the central and northern High Plains and in the Upper Midwest. ...Central and Northern High Plains... An upper-level low will remain over the Intermountain West on Friday as south-southwesterly flow continues in the High Plains. At the surface, a lee trough will deepen across eastern Colorado. To the east of the surface trough, southeast winds will help keep low-level moisture in place across the central High Plains. A narrow corridor of moderate instability will be possible by afternoon as surface temperatures warm. Convection that initiates in the higher terrain of eastern Colorado and eastern Wyoming will move north-northeastward into the lower elevations. NAM Forecast soundings at Scottsbluff, Nebraska for 00Z/Saturday show MLCAPE near 2000 J/Kg with 0-6 km shear of 40 to 45 kt. This combined with mid-level lapse rates from 7.5 to 8.0 C/km would support an isolated severe threat. Supercells and isolated large hail will be possible as cells move away from the mountains and into the stronger instability. However, there is some uncertainty with this scenario. The NAM develop the corridor of instability across west-central Nebraska but keeps the stronger mid-level flow further west from north-central Colorado into southeast Wyoming. The lack of overlap of instability and the stronger deep-layer shear could be problematic, keeping the severe threat area very small. For this reason, will leave a marginal in place across the central High Plains for the late afternoon and early evening. ...Upper Midwest... Southwest mid-level flow will be in place on Friday across the Upper Midwest. At the surface, a moist airmass should be located from the lower Missouri Valley extending north-northeastward into the western Great Lakes. Weak destabilization is expected along this corridor by afternoon. This combined with enhanced lift associated with a low-amplitude shortwave trough should be enough for scattered thunderstorm development, from northeastern Iowa into the Wisconsin. Mid-level flow is forecast to be around 35 kt across much of the upper Mississippi Valley on Friday. This combined with steep low-level lapse rates could be enough for marginally severe wind gusts. Hail could also occur with the stronger updrafts. ..Broyles.. 05/20/2021 Read more LIVE: