Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 13 2022 12:56:02 ACUS01 KWNS 131255 SWODY1 SPC AC 131254 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0654 AM CST Tue Dec 13 2022 Valid 131300Z - 141200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY AND TONIGHT FROM EAST TEXAS TO PARTS OF LOUISIANA AND MISSISSIPPI.... ....SUMMARY... Tornadoes (some strong), severe gusts and sporadic large hail are possible from southern Oklahoma and north and east Texas, to parts of Louisiana and Mississippi. ....Synopsis... A large mid/upper level cyclone -- initially covering most of the central/southern Rockies, High Plains, Great Basin, and Desert Southwest, is expected to shift northeastward across the central and northern Plains through the period. The main 500-mb low now is apparent in moisture-channel imagery over eastern CO near ITR, and should move to near ONL by 12Z tomorrow. Meanwhile, a basal shortwave trough -- now evident over southern NV -- will pivot through the southern semicircle of the cyclone. This perturbation should extend from southwestern OK to far west TX by 12Z. The associated surface low was analyzed at 11Z near MCK, with occluded front southeastward over west-central parts of KS/OK then southwestward across west-central/southwest TX near the Big Bend. The low should move slowly and erratically northeastward across the central High Plains through the period, until around 12Z when the mid/upper low catches up over northern NE. By 00Z, the cold front should reach parts of central/eastern MO, central AR, northwestern LA, and east-central/south-central TX, overtaking the more slowly eastward-progressing marine/warm front across northern LA. By 12Z, the marine/warm front should extend from near MOB to central/east- central MS, where the cold front overtakes it, with the cold front from there southwestward over central LA, the middle TX Coast, and deep south TX. ....Southern OK/north TX through midday... A broken band of convection, along/ahead of the surface cold front, is evident from western portions of central TX across south- central/east-central OK. This band has included a few supercells and embedded QLCS-type circulations during the predawn hours, and should continue to do so for at least a few more. Activity along and south of the warm front -- over southern OK and north TX -- will have the greatest potential to maintain surface-based effective inflow, with dewpoints in the 60s F. A wind profile and vertical- shear field favorable for continued mesocyclone development, and associated potential for a few tornadoes, should shift eastward across the region through midday. For near-term potential, see SPC tornado watch 581 and related mesoscale discussions. ....East TX and southern OK to lower Mississippi Valley region... The southern part of the near-frontal thunderstorm band, as well as isolated to scattered convection developing in the weakly capped warm sector, should maximize in intensity this afternoon into tonight. This activity will carry a threat for tornadoes (some potentially capable of EF2+ damage), severe gusts and isolated large hail. Strong low-level warm advection and moisture transport are expected through the day across the warm sector and over the warm-frontal zone. The associated increase in low-level moisture (60s F surface dewpoints) and theta-e, along with areas of slow/muted diurnal heating through cloud cover, will underlie cooling aloft to contribute favorable destabilization today. Though low/middle-level lapse rates are not expected to be particularly strong, weak MLCINH with MLCAPE in the 500-1500 J/kg range is expected from the warm- frontal zone to the Gulf Coast. Deep-layer wind fields should strengthen with time over the warm sector, with effective-shear magnitudes commonly reaching the 45- 60-kt range, to support supercells. Enlarged low-level hodographs are expected, with effective SRH commonly in the 200-400 J/kg range, with 150-250 J/kg 500-m SRH also possible. A mixture of linear, clustered and discrete modes is possible in this scenario, opening the potential for both supercellular and QLCS tornadoes, given the favorable low-level shear and at least adequate buoyancy forecast. The tornado threat in particular should persist across the Delta region tonight, especially near and south of I-20 where instability will be most favorable, but may extend into parts of the Mid-South amid weak CAPE as well. ...Edwards/Leitman.. 12/13/2022 $$ = = = 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) .