Administrators NorthGeorgiaWX Posted December 9, 2023 Administrators Share Posted December 9, 2023 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0644 AM CST Sat Dec 09 2023 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF THE MID-SOUTH AND DELTA REGIONS TO THE TENNESSEE VALLEY... ...SUMMARY... A few tornadoes, damaging to severe thunderstorm gusts, and isolated severe hail are possible today and tonight from portions of the Ohio Valley southward to the central Gulf Coast. ...Synopsis... In mid/upper levels, a positively tilted synoptic trough will amplify and proceed eastward across the central CONUS, predominantly in response to two accompanying shortwave troughs: 1. A northern-stream perturbation -- initially manifest as a closed cyclone over MN with trough southwestward over NE. This feature will devolve to an open wave across WI tonight, before reaching Lower MI and Lake Huron around 12Z tomorrow. 2. An elongated vorticity banner and speed max over the Four Corners States, which should reorient into a positively tilted trough by 00Z from southeastern KS across southwestern OK to southeastern NM. In doing so, it may absorb the southern portion of the northern-stream trough's vorticity field. By 12Z tomorrow, the reconfigured perturbation should extend from southern IL across central AR to south-central TX. The 11Z surface analysis showed a weakening, occluded low near HIB, with occluded front southeastward to a triple-point low near MKE. A cold front was drawn from there southwestward over the Ozarks to north-central TX and the Trans-Pecos region of west TX. By 00Z, the triple-point low will deepen into the dominant surface cyclone and eject northeastward to that portion of ON northeast of Lake Superior. The cold front should extend across central portions of OH/KY, southwestward over northern parts of MS/LA, to the middle TX Coast and deep south TX. The front should reach northern NY, central PA, WV, the TRI area, northern GA, southern AL, and the west-central Gulf by 12Z. ...Gulf Coast to Ohio Valley... Bands of scattered to locally numerous thunderstorms are expected to develop along and ahead of the cold front, perhaps as early as midday in northwestern areas of the outlook, but mainly from this afternoon through overnight hours. As activity sweeps eastward to northeastward over the region, damaging to severe gusts, sporadic hail near severe limits, and a few tornadoes are all possible. The tornado and wind threats should be relatively maximized from the Mid-South to Tennessee Valley region, given that area's probable overlap between the most favorable parameter space and thunderstorm probability. However, concerns over storm morphology -- particularly potential for messy/embedded convective modes and short duration of favorably mature supercell/mesocyclone production -- remain large. This notion is supported by the presence of short, low- to medium-magnitude UH tracks in the preponderance of CAM guidance. This does not preclude the possibility of a significant or longer-lived tornado threat locally, but makes it too conditional and uncertainly focused for a specific, greater-potential outlook area at this point. Deep shear and hodograph size will strengthen northward, with around 200-300 J/kg effective SRH being fairly common over the warm sector prior to arrival of the main frontal/ prefrontal band. With CINH being weak, additional convection may develop atop weak convergence zones in the nearby warm sector as well, especially over parts of northern AL and mid TN from late afternoon into evening, before either merging with or taking over as the main convective band. Forecast soundings show modest low/middle-level lapse rates beneath abundant cloud cover, with warm/theta-e advection contributing at least as much to surface destabilization as diurnal/diabatic warming. Surface dewpoints ranging from the upper 60s F near the coast to the 50s in the Ohio Valley (with temperatures not much warmer) will lead to a gently northward-diminishing buoyancy gradient. MLCAPE should range from around 1500-2000 J/kg over central/southern parts of the Delta region (where lift and shear will be weaker) to 500-800 J/kg over the Ohio Valley, in a prefrontal plume that narrows and has shorter duration with northward/inland extent. The eastern rim of the favorable surface-based buoyancy will shift across AL and into parts of GA, the FL Panhandle, eastern TN and perhaps western Carolinas overnight, supporting an eastward extension of marginal severe potential and more overlap with the start of the day-2 outlook area. ..Edwards/Gleason.. 12/09/2023 Read more View the full article Quote Link to comment Share on other sites More sharing options...
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