SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0149 PM CST Wed Feb 17 2021

Valid 172000Z - 181200Z


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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