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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.

Wednesday, October 20, 2021

SPC Oct 20, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1224 PM CDT Wed Oct 20 2021 Valid 211200Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO/TENNESSEE VALLEYS INTO THE CENTRAL/SOUTHERN APPALACHIANS...AND WEST TEXAS... ...SUMMARY... Showers and storms with isolated strong to damaging wind gusts will be possible Thursday across parts of the Ohio/Tennessee Valleys into the central/southern Appalachians. Isolated storms capable of marginally severe hail and strong gusts may also occur over a small portion of west Texas. ...Ohio/Tennessee Valleys into the Central/Southern Appalachians... An upper trough/low should move quickly eastward across the Great Lakes and Midwest through the day on Thursday. An attendant cold front will sweep eastward across these regions, much of the OH/TN Valleys, and into the southern/central Appalachians by Thursday evening. Limited low-level moisture, with surface dewpoints generally in the mid 50s to low 60s, is forecast to return northward ahead of the front. Modest diurnal heating, poor lapse rates, and cloud cover will likely limit how much boundary-layer instability can develop Thursday afternoon, particularly across the OH Valley and central Appalachians where low-level moisture will be less. Even so, low-topped showers and storms should develop by early Thursday afternoon along much of the length of the cold front. The weak forecast instability coupled with fairly strong west-southwesterly winds at low/mid levels should support some threat for isolated strong to damaging wind gusts as storms spread eastward through the day. Slightly greater instability may be realized from TN southward into AL/GA, but deep-layer shear should be weaker across this area than in the OH Valley. This isolated wind threat should quickly wane early Thursday evening as convection encounters the higher terrain of the Appalachians and a less favorable thermodynamic environment. ...West Texas... At least isolated storms should develop Thursday afternoon over the higher terrain of the Davis and surrounding mountains in west TX as a weak mid-level disturbance moves over this region. Although low/mid-level winds are forecast to remain fairly modest, there will be some veering of the flow with height, and steep low/mid-level lapse rates should also be present. Any storms that can form in this regime may pose an isolated hail and strong/gusty wind threat through early Thursday evening. ...Southern Oklahoma... Most 12Z guidance indicates the potential for convection across southern OK will be rather limited Thursday night into early Friday morning. While a storm or two may still develop, weak instability, marginal deep-layer shear, and meager large-scale ascent all suggest the threat for anything more than small hail should remain low. ..Gleason.. 10/20/2021 Read more LIVE: