SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0652 AM CST Sat Jan 02 2021 Valid 021300Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN FLORIDA PANHANDLE INTO SOUTHEASTERN GEORGIA... ...SUMMARY... Isolated strong to briefly severe thunderstorms may develop this afternoon and evening, from the eastern Florida Panhandle into southeastern Georgia. ...Synopsis... A strongly amplified, progressive, split-flow pattern dominates the CONUS this morning, the most prominent feature being a synoptic- scale trough from the western Ozarks region southwestward across OK and west-central TX, to north-central MX. This feature is expected to evolve a broadly closed 500-mb cyclone today over OK. The circulation center should reach the Ozarks of southern MO by 00Z, while a basal vorticity max now over north TX ejects over parts of AR and the Mid-South region. As the parent trough deamplifies considerably, and a strong, compact shortwave trough digs southeastward from the northern Rockies to the central High Plains, the mid/upper low should reach the OH/IN border region by 12Z tomorrow. At the surface, 11Z analysis showed an occluded low over NY near SYR, with a triple-point low near BID and cold front southwestward to eastern NC, becoming quasistationary to a weak frontal-wave low near AAF. The slow-moving cold front extended from there southwestward across the central Gulf. Another weak low should form along the front over the northern Gulf today and ripple northeastward along the boundary over the FL Panhandle and portions of GA today, delaying eastward shift of the frontal zone to its northeast until the low passes. The low should reach eastern NC by the end of the period. The front to its south will shift slowly eastward/southeastward, reaching eastern SC and the northwestern FL Peninsula by 12Z. ...FL Panhandle/Southeastern GA... Isolated strong-severe gusts are possible today into this evening in a corridor of thunderstorms along/ahead of the front, from the northeastern Gulf to parts of southeastern Georgia. As the mid/upper low ejects northeastward, largely abeam of this region, peripheral height gradients should tighten enough to strengthen both winds aloft and deep shear. Simultaneously, mass response to the distant passing wave will strengthen low-level mass convergence and theta-e advection within a pre-existing belt from the northeastern Gulf across the central/eastern FL Panhandle and parts of southern GA. Forecast soundings indicate boundary-layer theta-e will be just enough to yield marginal but uninhibited MLCAPE in the 300-800 J/kg range, amidst 40-50 kt effective-shear magnitudes favorable for at least transient supercellular characteristics. Forecast hodographs show about 150-250 J/kg 0-1-km SRH, with somewhat smaller effective SRH. The main limiting factors will include weak lapse rates (including within the boundary layer), leading to modest buoyancy, and the band-parallel nature of cell motion, contributing to messy convective modes. A strong preponderance of convective guidance indicates more-westward axis of the convective corridor, especially during the diurnal to early evening period when inflow-layer buoyancy will be relatively maximized. As such, the outlook area is shifted slightly back toward the front. ..Edwards/Leitman.. 01/02/2021
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