Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 04 2024 12:49:32 ACUS01 KWNS 041249 SWODY1 SPC AC 041247 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0647 AM CST Sun Feb 04 2024 Valid 041300Z - 051200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF SOUTHERN FLORIDA AND THE KEYS... ....SUMMARY... Severe thunderstorms are possible over southern Florida the next several hours and may develop again later today into tonight over parts of the peninsula. A low-end tornado threat may develop near parts of the central California Coast, mainly this afternoon. ....Synopsis... A highly amplified mid/upper level pattern will feature two substantial synoptic troughs/cyclones with convective implications: 1. A strongly negatively tilted trough from the central Rockies to the central/northern Gulf, with embedded circulation centers apparent in moisture-channel imagery over the TX Panhandle and northeast TX. The eastern center will take over and become a well-defined 500-mb low, moving southeastward across LA today into this evening, then over or just south of the western coastal FL Panhandle by 12Z tomorrow. Two basal shortwave troughs are apparent: a. Over the east-central Gulf, immediately preceded by a line of thunderstorms (see below), and forecast to eject northeastward over the FL Peninsula today. b. Over the lower/middle TX Coast, forecast to pivot southeastward then eastward across the central/eastern Gulf today and tonight, weakening as it approaches southwestern FL and the Keys between 06-12Z tomorrow. 2. A roughly south/north-elongated cyclone off the Pacific Coast, with several embedded vorticity maxima and at least transient circulation centers. The mean 500-mb center should remain offshore from northern CA trough the period, but drift eastward toward the coast. A well-defined, basal shortwave is evident west of southern CA near 130W, and should eject northeastward today, reaching the central CA coastline around 00Z. Surface analysis showed an occluded low inland of the Gulf Coast, over southern MS, and another low over the north-central/ northeastern Gulf around 125-150 nm south of MOB. A remnant Pacific cold front arched southeastward from that low, west of the Dry Tortugas, then southwestward toward the Yucatan Peninsula. This boundary should become more diffuse through the day, in deference to greater baroclinicity related to convective outflow just ahead of it. The low should move inland over the FL Panhandle this afternoon, reaching southeastern AL this evening before weakening. A warm front was approaching southwestern FL and the Keys, just ahead of the convection, and will remain close to the leading part of the thunderstorms as they cross south FL. ....FL... Multiple rounds of convection with at least marginal severe potential are possible through the period, with the greatest confidence in the "slight risk" area accompanying activity now approaching the southern part of the peninsula. This initial activity has formed and maintained as the large-scale ascent/DCVA and related low/middle-level lapse rates have shifted atop the warm Loop Current, aided by lift associated with a remnant Pacific front. A destabilizing (but not fully modified) return-flow airmass will immediately precede this activity across southern FL this morning, supporting potential for damaging gusts and isolated hail. An embedded tornado or two also cannot be ruled out. See tornado watch 14 and related mesoscale discussions for near-term details on this threat. A more-conditional severe threat will develop farther north, both over inland areas ahead of the northern part of the initial MCS, and in the zone of potential destabilization behind it. With residual moisture behind the morning complex, and perhaps a narrow corridor of moist advection around the western rim of the old outflow pool, around 500-1500 J/kg MLCAPE may develop by late afternoon. This will be possible as strong cooling aloft overlies a corridor of diabatic surface heating/destabilization. Favorable deep shear (effective-shear magnitudes 50-65 kt) will be present. The largest hodographs will be present from midday into mid/afternoon with southeasterly near-surface winds, however, that flow will be advecting convectively processes air from south FL. Hodographs should shrink thereafter, but still remain somewhat favorable for supercells. Uncertainties on convective coverage and amount of recovery behind the initial complex still preclude greater unconditional probabilities. Overnight, additional MCS development is progged over the central Gulf ahead of the second shortwave trough, but with the activity possibly weakening as it approaches southern FL and the Keys the last few hours of the period. That trend would be related to both nocturnal stabilization inland, and weakening/ejection of the shortwave trough northeastward away from the complex. Still, potential may exist for strong to marginally severe convection to reach these areas before 12Z. ....CA... Net columnar destabilization related to low-level warm advection, then midlevel cooling, should occur through the day. This, atop the moist marine layer, should lead to just enough destabilization of low/middle-level lapse rates for surface-based convection, including sporadic thunderstorms. SBCAPE and MLCAPE in the 100-300 J/kg range should become common after about 21Z. Time series of forecast soundings suggests a few-hour window where flow is not yet too veered to support enlarged hodographs and supercell-favorable deep shear, with effective-shear magnitudes around 35-45-kt possible. Given these profiles, fast-moving, low-topped convection may pose a threat for strong to marginally severe gusts and/or a brief tornado. ...Edwards/Leitman.. 02/04/2024 $$ = = = 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) .