Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 22 2024 12:43:55 ACUS01 KWNS 221243 SWODY1 SPC AC 221242 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 AM CDT Fri Mar 22 2024 Valid 221300Z - 231200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE FLORIDA KEYS INTO A SMALL PART OF SOUTHERN MAINLAND FLORIDA... ....SUMMARY... Severe thunderstorm gusts, isolated large hail and a tornado or two are possible today and tonight over parts of the Florida Keys into a small part of southern mainland Florida. ....Synopsis... In mid/upper levels, a slow-moving/cutoff low west of coastal northern CA and OR will approach the coast slowly through the period, but remain offshore until day 2. Downstream, a progressive, split-flow pattern is evident over the central/eastern CONUS, with a broad yet distinct northern-stream jet across parts of the Upper Midwest, Great Lakes, and Northeast. To the south, a prominent, southern-stream shortwave trough was apparent in moisture-channel imagery over eastern OK and east TX, with intermittently closed 500-mb low between MLC-PRX. This perturbation should become a purely open-wave trough today and broaden somewhat, with the trough near a MEM-LFT axis and offshore from southwestern LA by 00Z. The 12Z/tomorrow trough position should reach to near an axis from CHA-MGM-PNS to the central Gulf. At the surface, 11Z analysis showed a broad area of low pressure from north-central/northeast TX to south-central LA, including a frontal-wave low near ARA. A cold front extended from that low southwestward across the TX shelf waters to south of BRO, and should sweep eastward-southeastward to the central/southwestern Gulf by 00Z, when the low reaches southern AL. A warm front -- initially extending from the low eastward over coastal LA then southeastward over the eastern Gulf, should move northeastward toward the north- central/northeastern Gulf Coast and south FL/Keys today, but with some diffusion/realignments of its baroclinicity by convective processes. By the end of the period, the low should reach the Piedmont of the Carolinas, with cold front over GA and the eastern Gulf. Multiple rounds of convection will cross the east-central/ northeastern Gulf through the period on either side of the warm front. Convection should be most consistently intense over the Gulf, but potentially brushing coastal/near-coastal parts of the areas discussed below. ....South FL/Keys... At least isolated severe gusts and/or hail are possible across portions of south FL and the Keys, with the available instability and severe threat increasing southward. Multiple rounds of convection over the eastern Gulf should lay down boundaries acting as both foci and poleward delimiters for organized severe potential of upshear convection. Based on lightning, satellite and radar imagery, the first of these complexes extends from just offshore from APF west-southwestward to near 24N88W, with a patchy precip shield extending eastward and northeastward over much of the peninsula. That precip/cloud cover should blunt most of the diabatic heating-related overland destabilization today, though theta-e advection (especially over the Keys and vicinity) should yield surface-based buoyancy gradually over the next several hours. Most convection-allowing guidance has shrunk/weakened the leading complex considerably while approaching south FL and the Keys this morning, but also, has failed to grasp its southwestward extent so far. As such, mesoscale uncertainty persists as to the ultimate location and layout of the associated outflow boundary. Still, the general idea of greater unconditional severe potential with southward extent remains valid -- be it from the remains of the ongoing activity or, more likely, a later MCS now over the central/ north-central Gulf and expected to turn southeastward along the boundary and toward the outlook area, arriving tonight. Along and south of the boundary, where the near-surface layer is least modified by prior activity, upper 60s to low 70s F surface dewpoints should offset modest midlevel lapse rates aloft enough to yield 1000-1500 J/kg MLCAPE by this evening. Forecast soundings suggest favorable veering of winds with height into strong mid/upper-level flow, with 50-60-kt effective-shear magnitudes. Damaging winds and a tornado or two will be the main concerns. ....Southeastern LA to FL coastal bend... An ongoing, predominantly elevated area of thunderstorms -- from portions of southeastern LA southwestward across the LA shelf waters -- should proceed eastward near the north-central/northeastern Gulf Coast today. Additional development is possible to its east, also over shelf waters and/or the Gulf Coast. Isolated, marginally severe gusts or hail may occur. Activity should continue to move eastward in step with partial destabilization/recovery in the form of low-level warm advection and moisture transport, around and atop outflow from a complex of thunderstorms now over the east-central open Gulf. Enough theta-e recovery in low levels has occurred to support continued organization of the main MCS near the LA coastline, but at strong/ subsevere levels. This general trend should continue as activity shifts eastward across coastal MS/AL/FL Panhandle and offshore, amidst 60-70-kt effective-shear magnitudes and strong midlevel winds supporting fast convective translation. As such, momentum transfer from midlevels (via rear-inflow-jet processes or directly in individual/embedded downdrafts) may produce gusts capable of penetrating to the surface near severe levels. Favorable deep shear and lapse rates aloft also will persist eastward for hail production aloft, some of which may reach the surface near severe limits as well. ...Edwards/Grams.. 03/22/2024 $$ = = = 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .