Administrators NorthGeorgiaWX Posted March 5 Administrators Share Posted March 5 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0653 AM CST Tue Mar 05 2024 Valid 051300Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE ARKLATEX TO THE LOWER MISSISSIPPI VALLEY...AND PARTS OF PENINSULAR FLORIDA... ...SUMMARY... Strong to marginally severe thunderstorms are possible today over the region from the Arklatex to the lower Mississippi Valley, then mainly tonight over parts of peninsular Florida. ...Synopsis... In mid/upper levels, a low-amplitude, zonal to gently cyclonic flow pattern is present over most of the CONUS, ahead of a synoptic trough over the northeastern Pacific between 130W-140W. That trough will approach coastal northern/central CA near the end of the period with an embedded 500-mb low west of MRY, then move inland on day 2. Downstream, a southern-stream shortwave trough -- with several associated/small-scale vorticity maxima -- was apparent in moisture-channel imagery over eastern parts of OK/TX to the mid/upper TX Coast. This feature is expected to shift eastward across the Gulf Coast States and northern Gulf through the period, reaching parts of MS/AL and the FL Panhandle by 00Z, then moving across GA/FL in piecemeal fashion around the end of the period and early day 2. A weaker perturbation -- initially evident over parts of the Mid-Atlantic region and adjoining ocean waters -- should deamplify as it moves northeastward across New England through tonight. At the surface, a cold front was analyzed at 11Z from western QC across Lake Huron to southern MO, southeastern OK, north-central TX, and the TX South Plains region. A weak, attached low initially east of DAL should drift southward with the boundary and weaken further today, while another frontal-wave low forms ahead of the front over northern AL overnight. The front itself should move slowly southward across central/east TX, AR, and the lower Ohio Valley through the period. ...Arklatex to lower Mississippi Valley/Delta regions... The threat for marginally severe hail is ongoing with widely scattered elevated thunderstorms ongoing over portions of AR into the Arklatex region and nearby LA/east TX. Though predominantly multicellular in character, due to lack of more intense vertical shear, MUCAPE in the 1000-2000 J/kg range, supported by patches of favorable low-level moisture away from convectively modified air masses, should continue to support episodic development generally shifting eastward to east-southeastward across the outlook area into this afternoon. Sporadic large hail on a pulse basis will remain a threat, though isolated damaging to severe gusts cannot be ruled out as well. Several clusters or small complexes of thunderstorms may develop as the morning activity moves toward the lower Mississippi Valley, with the messier mode lessening hail potential locally but maintaining some pulse-wind threat. Strongest mid/upper winds also will be displaced over the Great Lakes and northern Gulf in distinct northern and subtropical streams -- north and south of the greatest concentrations of convection. This should maintain modest deep shear and a mostly multicell mode for inland activity. Though the prefrontal boundary layer should destabilize diurnally, especially over western parts of the outlook area ahead of the cold front -- mid/upper forcing for ascent will be displaced farther east into the Delta region with time -- and ultimately over parts of the Southeast containing less-suitable low-level moisture and instability. Though isolated strong-severe afternoon thunderstorms may form closer to the front in east TX, AR and LA, large-scale subsidence behind the trough will foster stable layers that may inhibit sustained convection over the greatest low-level instability today. With associated coverage uncertainties, overall unconditional severe probabilities are kept at marginal levels for the time being. ...FL... As the large-scale ascent/destabilization passes over the north- central/northeastern Gulf waters -- including the Loop Current -- low/middle-level lapse rates should steepen with weakening MLCINH. This may support upscale organization of convection now near and off the northern coastline into a quasi-linear MCS that would move east-southeastward across the Gulf, reaching the West Coast of FL late this evening or overnight, before shifting eastward over at least parts of the peninsula. Additional convection may form late during the diurnal heating cycle this afternoon, and/or in a zone of increasing warm advection and low-level convergence/lift ahead of the MCS this evening. While both synoptic and convection-allowing guidance is inconsistent on mesoscale timing of the complex, or greatest coverage areas of pre-MCS activity, the general notion of increasing convective potential from late afternoon onward over FL is supported by the pattern and by ongoing offshore convective trends. As such, while the severe threat still looks conditional (especially given some nocturnal stabilization likely to occur inland over FL), at least a marginal unconditional risk now is apparent, given increasing deep shear progged across most of the area, and at least marginal low-level instability with around 500-1500 J/kg MLCAPE away from convective outflows. Progged hodographs generally are not particularly large, though storm-scale and boundary interactions can modify them locally to become more favorable, amidst 35-45-kt effective-shear magnitudes. ..Edwards/Jewell.. 03/05/2024 Read more View the full article Quote Link to comment Share on other sites More sharing options...
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