Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 01 2023 13:01:44 ACUS01 KWNS 011301 SWODY1 SPC AC 011300 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0700 AM CST Wed Mar 01 2023 Valid 011300Z - 021200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH TEXAS TO PARTS OF THE TENNESSEE VALLEY REGION... ....SUMMARY... Severe-thunderstorm potential today through this evening is greatest from north Texas to parts of the Tennessee Valley region, with a few tornadoes, sporadic large to very large hail, and damaging wind all possible. ....Synopsis... In mid/upper levels, the main synoptic-scale feature for the CONUS will be a strong trough -- now apparent in moisture-channel imagery from the northern Rockies to a basal vorticity max over north- central CA, then southeastward down most of the CA coastline. As the northern part of this trough separates and crosses MT through 12Z tomorrow, a split-flow pattern will develop around the vigorously cyclogenetic southern portion. By 00Z, a closed 500-mb low should be located over the southern CA deserts near DAG, with trough northeastward over UT and south-southeastward down Baja. The associated cyclone should proceed east-southeastward across AZ through the remainder of the period, crossing southern AZ, with the low near SAD by 12Z. Downstream, a broad fetch of southwest to west-southwest flow aloft will cover most of northern MX and the south-central/southeastern CONUS. Embedded in that, a subtle perturbation now over the Edwards Plateau region will move across central TX and the Arklatex/Mid- South regions through the day. Other, weaker vorticity lobes may lurk beneath a cirrus canopy now streaming from the Baja spur across NM and west TX. That cloud swath should shift eastward, reaching from the Big Bend region northeastward past the Ozarks by 00Z. At the surface, a somewhat complex pattern is evident with a warm/ marine front analyzed at 11Z from central parts of GA/AL/MS across southern AR and parts of north TX, to the Hill Country. This boundary and the warm/moist sector to its south will continue moving northward through the day, possibly held up on the mesoscale by areas of precip related to convection developing in the next few hours over parts of north TX. This front will merge with a currently slow-moving cold front -- drawn at 11Z from a triple-point low over southwestern MO across south-central OK, northwest TX and the Permian Basin. Weak cyclogenesis is forecast on the combined frontal zone over north-central TX/southeastern OK through midday, ahead the leading mid/upper perturbation, rippling northeastward over the Mid-South region by 00Z. An occlusion/triple-point low should form by 00Z over OH, with cold front southwestward across southeastern MO. Except for mesobeta-scale oscillations, the front should remain quasistationary through 00Z on its segment from northwestern AR across southeastern OK and north-central/northwest TX. BY 12Z, the northern low should reach the near-coastal northern Mid-Atlantic or western New England area, with cold front extending to WV, middle TN, and south-central AR, becoming quasistationary across the Red River region of TX/OK, then a warm front near an area of early-stage surface cyclogenesis in northern NM. ....North TX to TN/OH Valleys... Multiple episodes of thunderstorms are likely through the forecast period, generally over northern and western parts of the outlook area today, shifting eastward to northeastward this evening into tonight. A few tornadoes, large hail (potentially significant/ damaging in western areas), and sporadic severe gusts are anticipated. Befitting the complexity of the surface pattern and the subtle/weak nature of large-scale forcing, the convective scenario through the period maintains considerable uncertainty on timing/location specifics, beyond the next few hours. While mesoscale concentration(s) of greater severe potential may manifest within this corridor, a general 15% wind/hail and 5% tornado outlook will be maintained for now. Spatially small expansion of the "slight" equivalent probabilities and significant-hail threat is warranted back into the Metroplex to account for severe potential from either evolution of ongoing development, or this afternoon's activity. In the near term, thunderstorms will offer mainly a hail threat over north-central TX; see SPC mesoscale discussion 213 for more details. That convection may weaken during a relative midday minimum in overall ascent near or just past the Metroplex, though some progs continue it northeastward into southeastern OK as the boundary layer destabilizes this afternoon. Whether as a continuation or expansion of that, or new development this afternoon, or some combination of both, scattered thunderstorms should occur again by mid/late afternoon over parts of north-central/northeast TX into southeastern OK. This activity then should shift into AR and the Mid-South through this evening, while additional convection forms near the front over the Ohio Valley. Warm/moist advection, muted diurnal heating, and frontal lift will support the convection, with favorable deep shear present under the broad west/southwest mid/ upper-level flow field. Peak/preconvective MLCAPE should reach 1500-2000 J/kg this afternoon in a narrow corridor from north TX to southeastern MO, decreasing to around 500-1000 J/kg over southern IN and middle TN. Despite light (5-10 kt) and somewhat veered surface winds ahead of the front, effective-shear magnitudes around 55-65 kt are forecast from north TX to western TN, diminishing to around 45-55 kt over the Ohio Valley -- all supporting supercell potential, along with 150-250 J/kg effective SRH in most of those areas. Upscale clustering is possible, with storm mode getting generally messier and more chaotic into the evening, though embedded or discrete supercells still will be possible. ...Edwards/Kerr.. 03/01/2023 $$ = = = 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) .