Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 21 2023 05:53:17 ACUS01 KWNS 210553 SWODY1 SPC AC 210551 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1251 AM CDT Thu Sep 21 2023 Valid 211200Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF CENTRAL NEBRASKA...FAR NORTHERN KANSAS...SOUTHERN OKLAHOMA AND NORTH TEXAS... ....SUMMARY... Thunderstorms, associated with large hail and wind damage, will be possible this afternoon and evening across parts of the southern and central Plains. An isolated tornado threat, along with a potential for very large hail, may develop in parts of southern and central Nebraska. ....Central Plains... A shortwave ridge will move eastward into the mid Missouri Valley today, as southwest flow becomes established at mid-levels across much of the central Plains. At the surface, a low will deepen in northeast Colorado as flow remains backed to the southeast across much of the central Plains. A moist airmass will be in place across Kansas and Nebraska where surface dewpoints will mostly be in the lower to mid 60s F. As surface temperatures warm, a southeast-to-northwest corridor of moderate instability is forecast to develop from central Kansas to southwest Nebraska. Convective initiation will be most likely on the northern end of this corridor, ahead of a distinct mid-level vorticity maximum. A cluster of storms is expected to organize and move east-northeastward across central Nebraska during the late afternoon and early evening. RAP forecast soundings by late afternoon along the instability axis near McCook, Nebraska have MLCAPE near 2500 J/kg, 0-6 km shear around 40 knots and 700-500 mb lapse rates between 8 and 8.5 C/km. This will be favorable for supercells with large hail and wind damage. The more intense updrafts may be able to produce hailstones greater than 2 inches in diameter. In addition, 0-3 storm-relative helicity is forecast to be between 300 and 400 m2/s2 during the late afternoon, suggesting a tornado threat will be possible. The severe threat is expected to persist into the early to mid evening, as the low-level jet gradually strengthens across the region. Further to the south into parts of western Kansas, convective initiation is expected to remain more isolated due to weaker large-scale ascent. Although the environment will be slightly less favorable further south, any cell that can become sustained could have potential for hail and marginally severe gusts. ....Southern Plains/Ark-La-Tex... Southwesterly flow at mid-levels will be in place today from the Desert Southwest into the southern High Plains. A shortwave trough is forecast to move eastward across the southern Plains. At the surface, a moist airmass will remain from parts of central and east Texas extending northward into Oklahoma. As surface temperatures warm, scattered thunderstorms are expected to form and move eastward across Oklahoma and north Texas. Multiple small clusters of thunderstorms will likely become organized in the early to mid evening, moving eastward towards the Ark-La-Tex. Warming surface temperatures during the day, along with dewpoints in the lower to mid 60s F, will result in moderate instability across much of north Texas and Oklahoma. MLCAPE is forecast to peak in the 2000 to 2500 J/kg range over much of this airmass by late afternoon. This, combined with about 40 knots of 0-6 km shear, evident on forecast soundings, will likely be favorable for supercell development. Supercells will have potential for isolated large hail and wind damage. Further west into parts of the eastern New Mexico and west Texas, some models suggest that moderate instability will be in place by late afternoon. Although thunderstorm development is expected to remain isolated, moderate deep-layer shear and steep mid-level lapse rates could support a marginal severe threat during the late afternoon and early evening. ...Broyles/Bentley.. 09/21/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .