SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0249 PM CDT Sat Oct 18 2025 Valid 182000Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT FROM THE ARK-LA-TEX TO THE LOWER OHIO AND MISSISSIPPI VALLEYS... ...SUMMARY... Scattered severe thunderstorms are possible mainly this afternoon into tonight across parts of the Ark-La-Tex, Ozarks, mid to lower Mississippi and lower Ohio Valleys. Damaging winds, a few tornadoes and hail may occur. ...20Z Update... Given the progression of the shortwave trough in the southern Plains, severe probabilities have been removed behind ongoing convection from parts of northeast Texas into western Arkansas and southwest Missouri. The 18Z soundings from Shreveport and Little Rock show modest mid-level lapse rates and low-level shear. The wind profile is expected to improve somewhat later this afternoon into the early evening. Discrete showers and thunderstorms are steadily increasing in intensity in the ArkLaTex region. As this activity move north and east over the next several hours, it will pose a locally higher tornado threat so long as storm mode remains favorable. Additional forecast details can be found in the previous forecast below. Other short-term details are in MCD 2152. ..Wendt.. 10/18/2025 .PREV DISCUSSION... /ISSUED 1117 AM CDT Sat Oct 18 2025/ ...Synopsis... A southern stream shortwave trough will eject quickly east-northeastward from TX/OK to AR/MO, prior to phasing with an amplifying northern stream trough by tonight across the mid MS Valley. Downstream from the phasing troughs, a deepening surface cyclone will develop northeastward tonight from the mid MS Valley to Lower MI, as a trailing cold front surges southeastward from the Plains into the mid-lower MS Valley. ...TX/OK today into the MS/OH Valleys through early Sunday... Regional 12z soundings revealed a plume of 7.5-8 C/km midlevel lapse rates (FWD-OUN-LMN) atop low-level dewpoints in the 60s, which is already contributing to moderate buoyancy (MUCAPE up to 1500 J/kg) as of mid morning. As continued forcing for ascent with the lead shortwave trough overspreads the moisture/buoyancy plume, ongoing thunderstorms are expected to increase in coverage through the afternoon from southern MO/IL to eastern OK/western AR and north/northeast TX. Initial storms will be in the form of clusters/short line segments with upscale growth into a more extensive squall line expected by later this afternoon/evening. Buoyancy will increase some in the moisture plume through the afternoon with surface heating in cloud breaks, and deep-layer vertical shear will increase with the approach of the ejecting midlevel trough. Thus, the stronger embedded cells will have the potential to produce large hail (1-1.75 inches in diameter) along with an increase in the threat for wind damage as convection becomes more linear. The tornado threat is a bit more uncertain given the early/messy start to convection this morning, and since low-level shear will not be strong this afternoon in the warm sector as a result of primary cyclogenesis not occurring until tonight from IL into lower MI (north of the richer low-level moisture). Still, a couple of tornadoes may occur with embedded circulations. There will be the potential for more discrete supercells and a few tornadoes ahead of the larger-scale line of storms from far east TX into LA/southern AR and MS overnight where boundary-layer dewpoints exceed 70 F and low-level shear increases. Though buoyancy will be weak, rapidly strengthening wind fields overnight and forcing for ascent along the synoptic cold front could support a low-topped line of convection with the potential for wind damage and possible a couple of embedded tornadoes from the OH Valley into southeast Lower MI ~06-12z.
