Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 18 2025 19:52:37 ACUS01 KWNS 181952 SWODY1 SPC AC 181950 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0250 PM CDT Thu Sep 18 2025 Valid 182000Z - 191200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF MISSOURI... ....SUMMARY... Isolated severe storms are possible mainly from late afternoon into tonight across Missouri into adjacent parts of the Lower Missouri Valley and southern Plains. Isolated strong to severe storms may also occur across southern California and the Lower Colorado River Valley. ....20z Update... The previous forecast remains on track. The primary adjustment was an eastward expansion of 5% wind/hail probabilities into northwest AR where pulse convection is developing within a very buoyant (though weakly sheared) environment. Similar thermodynamic/kinematic conditions have yielded sporadic wind/hail reports in recent days, so at least a low-end severe threat is anticipated through early evening (see MCD #2096 for additional details). Elsewhere, the forecast remains on track. Convection is beginning to deepen across northeast OK, far eastern KS, and far southwest MO, which is expected to increase in coverage and intensity within the Slight risk area through the evening based on recent environmental data and CAM solutions. Further west, consideration was given for removing risk probabilities across eastern TX into western OK; however, surface convergence along a diffuse front is gradually increasing with an attendant uptick in mid-level cumulus. Forecast soundings and a couple of recent HRRR/RRFS solutions hint that elevated convection along the boundary remains possible through mid-evening, and deep-layer wind shear is sufficient for organized convection. Across central OK, elevated thunderstorms developing late tonight within a modest warm advection regime may pose a threat for isolated large hail. See the previous discussion below and MCDs #2097 and #2098 for additional details. ...Moore.. 09/18/2025 ..PREV DISCUSSION... /ISSUED 1139 AM CDT Thu Sep 18 2025/ ....Missouri and Lower Missouri Valley to southern Plains... Generally isolated severe storms will be possible today regionally ahead of the east/southeast-advancing front (and residual convection/outflows), but a somewhat greater/semi-focused corridor of severe potential, mostly in the form of damaging winds, appears to exist across portions of Missouri. This will be influenced by modestly stronger cyclonic flow aloft attendant to the mid/upper-level trough, with a favorably warm/moderately unstable boundary layer this afternoon. Bouts of damaging winds will be possible regionally, with some hail as well. ....Southern California/Lower Colorado River Valley.... An anomalously moist airmass associated with the remnants of tropical cyclone Mario continues to advect northward into and across southern portions of California/Arizona. 12Z NKX sounding sampled a 1.95 PW value, which is well above the 90th percentile based on daily SPC sounding climatology. Filtered heating is anticipated within this moist environment, resulting in moderate buoyancy across much of eastern southern California and southwest Arizona this afternoon. Moderate vertical shear is anticipated as well, particularly across southern California. Additional thunderstorm development is expected during the afternoon, with a predominantly multicellular mode. However, enough shear and instability are in place to support organization with any more persistent updrafts, and a few supercells capable of damaging gusts are possible. A very-low-probability tornado threat may exist as well, particularly in the Lower Colorado Valley vicinity where some guidance suggests surface winds stay more southeasterly. Even so, the low-level flow is weak and any tornado threat should be very localized. ....Eastern South Dakota/southeast North Dakota/western Minnesota... In proximity to the upper low over the Dakotas, a relatively moist environment, sufficient cloud breaks/heating, ample low-level CAPE, and ambient vorticity near a weak surface low and nearby front could be sufficient for some funnels this afternoon through around sunset. A brief non-supercell tornado cannot be conclusively ruled out near the boundary/surface low if stronger destabilization materializes, but the overall potential/likelihood should remain limited. $$ = = = 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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .