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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.

Sunday, May 7, 2023

SPC May 7, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1253 AM CDT Sun May 07 2023 Valid 071200Z - 081200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS FAR EASTERN NEBRASKA...EXTREME NORTHEAST KANSAS...MUCH OF IOWA...FAR NORTHERN MISSOURI...AND EXTREME WESTERN ILLINOIS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF NORTHWEST TEXAS INTO FAR SOUTHWEST OKLAHOMA... ...SUMMARY... Severe storms with very large hail, hurricane force gusts, and isolated tornadoes will be possible across parts of the Mid Missouri Valley today. Severe wind/hail producing storms will also be possible in parts of the central and southern Plains, perhaps extending into parts of the southern Great Lakes and Ohio Valley into the Tennessee Valley and central Appalachians. ...Synopsis... An upper ridge will remain in place east of the MS River as a mid-level trough slowly traverses the Interior West today. Multiple mid-level impulses will crest the ridge through the period, supporting the development of multiple MCSs across the Mid MS Valley into the OH/TN Valleys and central Appalachians. Meanwhile, surface lee troughing and northward low-level moisture advection will persist across the Plains states. A dryline will gradually push eastward through the afternoon, initiating strong to severe thunderstorms in a very unstable environment. ...Mid MS Valley... Ahead of the surface lee trough, a diffuse warm front will stall across eastern NE into IA and western IL by afternoon. Along and south of the warm front, mid to upper 60s F surface dewpoints overspread by 8.5+ C/km mid-level lapse rates (resulting in over 4000 J/kg MLCAPE) will characterize the warm sector. Veering and strengthening vertical wind profiles along the warm front will also support sizable, curved hodographs, especially in central IA. The approach of a mid-level impulse and strong surface heating will support isolated supercell development by late afternoon along the warm front. Very large hail and a few tornadoes will be the initial threats with these storms, and a strong (EF2+) tornado cannot be ruled out. Around and just after sunset, several thunderstorms are expected to initiate along the surface lee trough/warm front intersection in eastern NE/extreme northeast KS. While large hail may accompany these storms, rapid upscale growth should result in the development of an intense MCS, with severe winds becoming the main threat. It is possible that a classic bow-echo MCS may develop by evening, supporting widespread severe winds (with a few gusts exceeding 65 kts possible). However, confidence in this scenario is too low for the introduction of higher wind probabilities at this time. ...OH/TN Valleys into the central Appalachians... Multiple MCSs will track across areas east of the MS river into the OH/TN Valleys through the forecast period. At the start of the day (12Z), an MCS is poised to be moving southeast across the OH Valley. This MCS will approach the central Appalachians by early afternoon, preceded by 6.5-7.5 C/km low-level lapse rates, contributing to 500-1000 J/kg MLCAPE. Given modest line-normal speed shear, the MCS may remain organized enough to produce a couple of damaging gusts through the morning/early afternoon hours before dissipating. Latest guidance consensus depicts a second MCS developing along the eastern fringes of a low-level warm-air advection regime somewhere along the MS river into the OH/TN Valley areas by mid-afternoon, when surface heating will have boosted surface temperatures to near 80 F amid upper 60s F dewpoints, overspread by 8 C/km mid-level lapse rates. 2500 J/kg SBCAPE amid 30+ kts of effective bulk shear will precede this second MCS, supporting a threat for at least isolated damaging gusts. The primary mitigating factor for introducing higher wind probabilities this outlook over the OH/TN Valleys is the uncertainty of placement and timing of the second MCS. ...Southern Plains... Rapid thunderstorm development is likely by afternoon peak heating ahead of the dryline across portions of western TX. Initial updrafts will benefit from over 4000 J/kg MLCAPE, driven by steep low and mid-level lapse rates. Effective bulk shear should remain modest (i.e. under 30 kts), with multicells and perhaps a few supercells likely initially. Large hail will be the main threat early on. However, storms should quickly become outflow dominant given weak low-level shear, with cold pool mergers anticipated. Upscale growing clusters will support severe wind gusts as the primary threat. Similar to the previous day, northward surging outflow from decaying storms will promote damaging gust potential into southern and central OK by evening. ...Northern High Plains... Boundary-layer mixing and upslope flow along the Black Hills of western SD will support thunderstorm development by afternoon peak heating. These storms will progress eastward amid 7.5-8.5 C/km low-level lapse rates and modest speed shear, contributing to elongated, straight hodographs. Any storms that can mature and sustain themselves may take on multicellular or transient supercellular characteristics with the potential to produce a severe gust or two before nocturnal cooling/boundary-layer stabilization sets in around sunset. ..Squitieri/Lyons.. 05/07/2023 Read more CHECK UPDATE ZOOM GRAPHIC