Administrators NorthGeorgiaWX Posted March 6 Administrators Share Posted March 6 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0652 AM CST Wed Mar 06 2024 Valid 061300Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF PENINSULAR FLORIDA...SOUTH CAROLINA AND PARTS OF WEST-CENTRAL TO NORTH TEXAS... ...SUMMARY... Isolated severe thunderstorms are possible today over parts of peninsular Florida and South Carolina, and late afternoon into tonight over parts of west-central to north Texas. ...Synopsis... In mid/upper levels, a progressive and amplifying pattern is forecast over the CONUS through the period, mainly related to a well-developed trough now approaching the CA coastline. The accompanying 500-mb low should move over the Point Conception area around 18Z, then weaken inland across southern CA overnight. However, the trough will remain strong as an open-wave feature, as it approaches the lower Colorado River Valley around 12Z. Downstream, a series of minor perturbations embedded in the subtropical/southern stream will traverse northern MX and much of TX. Farther east, a shortwave trough was quite evident in moisture-channel imagery over parts of TN, AL and GA, extending southward to the northeastern Gulf. This initially rather broad perturbation will consolidate somewhat and cross parts of GA and the western/upstate Carolinas by 00Z, then move northeastward into the Mid-Atlantic by the end of the period. At the surface, 11Z analysis showed a series of weak lows and troughs scattered across the Southeast amid weak surface flow, with a warm front along the SC and southern NC coast, then bending southeastward offshore from HSE. Northward movement of this boundary will be delayed by precip/clouds this morning, but should occur this afternoon across the inland Carolinas. Meanwhile, another frontal zone -- initially drawn over deep south TX -- should migrate northward as a warm front today and tonight across much of central/north TX and into OK tonight, connecting to overnight surface cyclogenesis progged for the northwestern TX Panhandle. ...FL... Widely scattered to scattered thunderstorms are expected to develop this afternoon along sea-breeze boundaries and smaller-scale zones of lift, amidst diabatically weakened MLCINH and favorable low-level moisture. The best-organized convection may produce damaging to isolated severe downdrafts and isolated severe hail. The southern fringes of cooling aloft related to the southeastern CONUS perturbation, atop upper 60s to low 70s F surface dewpoints, in a deep troposphere, will lead to peak/preconvective MLCAPE in the 1500-2500 J/kg range. Activity should be predominantly multicellular, with modest low/middle level flow limiting most measures of bulk shear. However, relatively strong upper/anvil- level winds will ventilate convection to some extent and contribute to around 50-70 kt of shear from LCL to EL. Near the East Coast sea breeze, some backed low-level flow is possible that may augment low-level and deep shear enough for at least transient storm-scale rotation and a marginal/brief tornado potential as well. ...SC and vicinity... An extensive plume of precip -- with isolated to widely scattered, sporadic, embedded thunderstorms -- is shifting roughly northeastward across parts of GA, the Carolinas and eastern TN. This activity is supported regionally by a combination of warm advection and moisture transport, with related modest, elevated destabilization. Severe conditions are not expected with this activity due to insufficiency of both buoyancy and shear. However, especially over the Low Country/coastal plain and perhaps central SC, a second round of convective development is expected late this afternoon into evening, offering marginally severe hail or strong/damaging gusts. This activity should follow several hours of airmass recovery through a combination of diabatic heating, continued low-level warm advection, and DCVA/cooling aloft nearer to the "cold-core" region of mid/upper-level perturbation. These processes should steepen low-level lapse rates and weaken MLCINH, while slightly increasing previously poor midlevel lapse rates by late afternoon. In combination with favorable near-surface moisture (dewpoints generally low/mid 60s F), this should support around 800-1200 J/kg MLCAPE. Though low-level hodographs/SRH/bulk shear shouldn't be large, around 30-40 kt effective-shear magnitudes are expected, with some organized multicell or transient supercell structures possible. Convection should weaken and exit the area by late evening. ...West-central/northwest/north-central TX... Isolated to widely scattered thunderstorms are possible from late afternoon into the overnight period -- initially over parts of the Big Country/Concho Valley regions of west-central TX, then spreading/shifting northward and northeastward with time tonight. Isolated severe hail is the main concern, though strong/locally severe gusts cannot be ruled out either. The northward-returning frontal zone appears to be the most probable source of low-level lift, through some chance exists for surface parcels to reach convective temperature on southwestern parts of the outlook area. Low-level warm advection and moisture transport/recovery will strengthen considerably from late afternoon through overnight across the region, as the Pacific mid/upper trough approaches, the subtle southern-stream perturbations move overhead, and southwest flow increases aloft. This should lead to increasing convective coverage, though uncertainty lingers on spatial extent and density, given the subtlety of overall lift. Environmentally, upstream high-cloud cover prevalent in satellite imagery should thicken through the day, lending further uncertainty to specific initiation timing/location, but still allowing enough heating to weaken MLCINH by late afternoon. CINH will weaken further this evening into tonight because of warm advection/ isentropic ascent to LFC -- particularly as the southerly LLJ strengthens overnight to around 40-50 kt. The moisture increase (especially above the surface) and warm advection will contribute to MUCAPE around 1000 J/kg, most of it in low/middle levels below a more-stable mid/upper regime related to the cloud deck. Some convective organization is possible, amidst 30-40 kt effective-shear magnitudes. ..Edwards/Jewell.. 03/06/2024 Read more View the full article Quote Link to comment Share on other sites More sharing options...
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