SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0149 PM CST Wed Feb 17 2021 Valid 172000Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL GULF COAST THROUGH TONIGHT... ...SUMMARY... Isolated to scattered damaging winds and a couple tornadoes are possible across a portion of the central Gulf Coast, after about 6 PM CST through the overnight. ...20z Update - Central Gulf Coast... The main changes with this update are to pull the Marginal risk southward across MS/AL/GA. Latest guidance suggests the surface warm front will hug the immediate coastal area from near the mouth of the MS River to near Mobile and the FL Panhandle. As a result, most convection will remain elevated and over a much cooler airmass across southern MS/AL and southwest GA. Instability will remain limited, but strong effective shear will result in some organized convection moving inland from the Gulf. In the vicinity of the surface warm front, low level SRH will be maximized, and the greatest threat for damaging gusts or a couple of tornadoes will be along the frontal zone. As a result, the Slight risk area remains unchanged from the previous outlook. ..Leitman.. 02/17/2021 .PREV DISCUSSION... /ISSUED 1028 AM CST Wed Feb 17 2021/ ...Central Gulf Coast... No change has occurred with the cat 1 and 2 (MRGL and SLGT) risk areas. Primary mitigating concern for expansion or greater probabilities is the extent of surface-based warm sector inland within a very tight baroclinic zone. Surface cyclone over the northwest Gulf is progged to gradually fill as it approaches the western FL Panhandle through late tonight. Thunderstorms are expected to initially develop near this cyclone and then expand in coverage during late afternoon into tonight, primarily from elevated parcels north of the warm front. Initial linear organization for severe potential will probably commence just offshore of the south-central LA coast by late afternoon. This activity should eventually overlap with the impinging of low to mid 60s surface dew points into a portion of southeast LA during the evening. Here, rather enlarged low-level hodographs coincident with 50-60 kt effective shear should yield potential for embedded supercell structures within the squall line, capable of producing a few tornadoes and damaging winds. The very tight baroclinic zone will be characterized by an increasingly sharp low-level inversion with northern extent likely limiting the areal coverage of tornado and damaging wind potential farther inland (this region recently warming above freezing as of 16Z). Given the strength of the flow aloft, it is plausible that line segments may spread quickly northeast and outpace the surface-based warm-sector before it reaches the FL Panhandle overnight. The eastern portion of the tornado/wind risk (near the central portion of the FL Panhandle) between about 09-12Z may emanate from convection that can form in pre-frontal confluence bands across the northeast Gulf.
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