SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0149 PM CST Thu Feb 18 2021

Valid 182000Z - 191200Z


A strong-to-severe storm or two are possible through this evening
from the eastern Florida Panhandle to the Georgia and far southern
South Carolina coasts. The main hazards with this activity are gusty
winds and perhaps a brief tornado.

...20z Update - FL Panhandle to south GA...

The Slight risk has been removed with this update. Convection has
struggled to maintain and/or increase in intensity this afternoon.
Much of the shower and isolated thunderstorm activity across the
region is elevated, on the cool side of the front, which now extends
from just south of Savannah GA to very near Tallahassee FL. Surface
heating into the mid 70s to mid 80s has occurred ahead of the front,
and dewpoints in the mid 60s to near 70 F are aiding in MLCAPE
values around 250-500 J/kg. Poor midlevel lapse rates will limit
further destabilization. Surface winds ahead of the front have
veered to the southwest, decreasing convergence along the boundary.
Nevertheless, moderate low level shear overlies the area and could
aid in brief upticks in intensity/organization of cells track
northeast over the next few hours. The overall severe threat however
appears marginal and limited in space and time, with any tornado
threat being quite conditional on a stronger storm actually
developing. As a result, the Slight risk has been removed, though a
Marginal risk remains from the eastern FL Panhandle to the GA and
far southern SC coasts.

..Leitman.. 02/18/2021

.PREV DISCUSSION... /ISSUED 1030 AM CST Thu Feb 18 2021/

...FL Panhandle to south GA...
Categorical risk areas have been mainly adjusted to decrease the
western and northern extent with a persistent, low probability
tornado environment expected to continue into this evening.

Overall lightning trends have decreased somewhat through late
morning within a swath of scattered convection that is elevated from
the eastern Carolinas to surface-based over the northeast Gulf. The
surface warm sector characterized by mid to upper 60s surface dew
points resides across the central to eastern Panhandle and north FL
into a portion of south-central to southeast GA. A lack of stratus
in north FL to southeast GA will result in more robust
boundary-layer heating and the front reaching the Savannah to
southwest GA vicinity before oscillating back south later today.
This heating will likely be necessary to aid in sustaining
surface-based thunderstorm redevelopment given the weak mid-level
lapse rates evident in 12Z observed soundings across FL.

Low-level southwesterlies should be strongest at present and slowly
subside into this evening, but at least 40 kt flow will likely
persist through late afternoon. With a lack of cyclogenesis,
low-level hodographs, while adequate for supercell development, are
unlikely to broadly improve. This suggests the severe threat may
remain conditional, and require convection to develop/spread towards
the warmer boundary layer farther east. A weakening trend should
ensue after sunset as the boundary layer cools and low-level
hodographs become increasingly marginal.

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