Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Wed Oct 11 2023 08:15:00 ACUS01 KWNS 111253 SWODY1 SPC AC 111251 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Oct 11 2023 Valid 111300Z - 121200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL/NORTHERN FLORIDA TO THE COASTAL-BEND REGION... ....SUMMARY... Damaging thunderstorm gusts and a few tornadoes are possible this evening and tonight over parts of central/northern Florida to the coastal-bend region. ....Synopsis... The mid/upper-level pattern features a couple synoptic-scale cyclones -- one centered over northeastern ON south of James Bay, the other near the western coastline of the Olympic Peninsula -- forming the feet of an apparent omega block with the anticyclone over north-central Canada. However, unlike many omega patterns on the timescale of a day, this one will be decidedly progressive, with the eastern cyclone continuing to fill and shift eastward back into QC. Meanwhile, the western cyclone -- currently accompanied by a negatively tilted trough extending southeastward over NV -- will weaken inland over WA/southern BC, while another forms along the trough tonight, over the south-central WY/northwestern CO vicinity. Height falls and strongly difluent, cyclonic flow aloft will spread east-southeastward across the central/southern Rockies and then the adjoining Great Plains by 12Z tomorrow. The intervening synoptic ridge -- now evident over the central/ northern Plains -- will shift eastward to MO/IA/MN around 12Z. By that time, the western cyclone, and the quasistationary mid/upper high over northern Canada, will form more of a Rex configuration. To its southeast, the mid/upper-level portions of former Pacific Hurricane Lidia (the low levels having been shredded in the lofty/ rugged terrain of central MX) are moving northeastward from central to northeastern MX. Associated vorticity banners aloft will cross deep south TX, the northwestern Gulf, and the central Gulf Coast. Though not very intense, enough low-level mass response is expected to aid frontal-wave cyclogenesis over the Gulf through the period. The surface warm front was analyzed at 11Z across south FL, bending northwestward over the northeastern Gulf south of AAF, then west- southwestward to a 100-mb frontal-wave low over the northwestern Gulf, roughly east of BRO and south of BPT. The low should ripple northeastward along the northward-moving segment of the boundary to near the mouth of the Mississippi River by 00Z, then weakening and moving eastward across northern FL by 12Z, with additional development possible on the frontal segment over the nearby Atlantic. Meanwhile, cyclogenesis will occur over eastern CO by 00Z, as the mid/upper trough approaches, with warm front eastward across northern MO and cold front southwestward across the Four Corners area. By 12Z, a well-developed low should be located near MCK, with cold front southwestward near an EHA-TCS line and warm front over east-central NE, southern IA and central IL. ....Central/northern FL to coastal-bend region... Areas of scattered to numerous thunderstorms should shift east- northeastward across the north-central/northeastern Gulf throughout the day and into tonight, and begin to impinge on coastal west- central/northwestern FL this evening and overnight. Additional activity may develop ahead of the Gulf convection, in a weakly capped and favorably moist inland boundary layer near the northward-moving front. A few tornadoes and damaging gusts appear to be the main threats. Density of convection, and related outflows, make severe potential more conditional with northward extent over the northern FL/eastern Panhandle area. Hodographs should enlarge throughout the afternoon and especially tonight over the outlook area, as the frontal-wave low approaches, low-level windspeeds above the surface increase in the associated mass response, and the front itself shifts northward with backed flow in the associated baroclinic zone. Modest nocturnal low-level lapse rates should limit buoyancy, with MLCAPE near and south of the front generally in the 500-1000 J/kg range inland (locally higher). Though modest for the geographic area, this can support surface- based supercells, given the presence of effective SRH commonly in the 150-250 J/kg range and locally larger. Some offsetting factors preclude a greater unconditional tornado risk at this time. An increase in forecast buoyancy near the western coastline, the last few hours of the period, coincides with veering of near-surface winds that also will reduce hodograph size/ SRH. Potentially dense/messy convective character and lack of larger near-surface instability also are factors. Still, at least a few potentially tornadic supercells appear possible within the broader mass of thunderstorms. With a preponderance of guidance reasonably indicating the eastward expansion of both a favorable supercellular parameter space and surface-based convective potential toward the Atlantic Coast before 12Z, the outlook area has been extended accordingly. ....Central Plains/Corn Belt... Ongoing/nonsevere convection over parts of western IL to northern MO and southern IA should remain so through the rest of the morning as the supportive low-level flow and isentropic lift weaken. A rogue hail core near severe levels cannot be ruled out, but appears improbable at this time, based on convective and environmental trends. The same elevated, low-level regime of warm advection and moisture transport contributing to that activity should shift/redevelop northwestward through today, then intensify considerably from late afternoon into tonight, amid the mass response to the approaching mid/upper trough. Increased transposition of cooling aloft and low-level theta-e advection will steepen lapse rates and increase buoyancy, while gradient flow aloft and deep shear also strengthen. The net result should be a band or two of scattered thunderstorms this evening and overnight, with episodic, marginally severe hail. Activity (especially in western areas of the outlook, over NE/SD) will be supported by a 30-50-kt LLJ east of the intensifying low-level cyclone, with around 1000-2500 J/kg MUCAPE and 30-40-kt effective-shear magnitudes. Though 850-mb flow is progged to be more difluent with eastward extent into IA/IL, sufficient speed convergence should exist to support lift of parcels to LFC and marginal hail potential there as well. While not likely, a marginal threat for a severe gust is indicated over parts of NE as well, by the presence of a somewhat dry, inverted-v character to much of the boundary layer depth underlying the elevated convective inflow region in forecast soundings. ...Edwards/Broyles.. 10/11/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .