SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0639 AM CST Tue Feb 09 2021 Valid 091300Z - 101200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not forecast through tonight across the contiguous United States. ...Synopsis... In mid/upper levels, a large, complex cyclone will remain over central Canada through the period, helping to maintain broadly cyclonic to zonal flow across most of the CONUS. Moisture-channel imagery indicates a lengthy but weak, strongly positively tilted perturbation from northern GA southwestward across deep south TX and northeastern MX. The northern portion of this perturbation will move offshore from the GA coastline by 18Z, with a weaker, trailing vorticity banner across northern FL and the northeastern Gulf. Farther west, a better-defined/southern-stream trough was apparent over the Pacific west of CA and Baja, roughly between 125W-130W. This feature should amplify somewhat and reach southern CA and northwestern Baja by the end of the period, but with insufficient levels of both lift and low-level theta-e resulting in lack of overland thunder potential. At the surface, 11Z analysis showed a frontal-wave low just offshore from PNS, with slow-moving cold front west-southwestward across the extreme northern Gulf, becoming quasistationary and diffuse over south TX. An intense, reinforcing cold front was analyzed from the Arklatex region across central TX to the Edwards Plateau, becoming quasistationary over eastern NM. The northeastern Gulf low will weaken near the west-central FL Panhandle coastline while another develops offshore from GA. The front should move little across the northern Gulf, pending being overtaken by the stronger front after this period. A warm front -- extending from the Gulf low east- southeastward across the northern FL Peninsula -- may reach the FL/GA line before this evening, then become quasistationary behind the Atlantic low. ...Southeast... Widely scattered to scattered thunderstorms are ongoing across portions of southern AL, southwestern GA and the FL Panhandle. This convection is rooted in a layer of elevated inflow of sufficiently modified Gulf air, lifted above the relatively stable near-surface layer north of the front. The supportive zone of warm advection and moisture transport is expected to shift eastward across GA and northern FL through today, weakening with time as the related midlevel perturbation moves away. However, in the meantime, bands of thunderstorms will continue to shift eastward over the outlook area, amidst MUCAPE in the 500-1000 J/kg range. Nearly surface- based parcels near the warm front may brush the immediate coastal area roughly between PAM-AAF in the next few hours before the bulk of convection passes the area, so locally strong nearshore gusts are possible. Latest objectively analyzed/RAP-based mesoanalysis data and forecast soundings through midday indicate 45-60-kt effective-shear magnitudes, amidst sufficiently steep midlevel lapse rates to support hail approaching severe limits with the most intense cells. While very isolated, brief, marginally severe hail cannot be ruled out, the threat still appears too conditional and sparse to warrant 5%+ probabilities that would trigger a categorical outlook area. ..Edwards.. 02/09/2021
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