SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0200 PM CST Mon Feb 15 2021

Valid 152000Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS INTO THIS
EVENING FROM THE FL PANHANDLE INTO SOUTHWEST GA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVERNIGHT ACROSS
PORTIONS OF THE COASTAL CAROLINAS...

...SUMMARY...
Scattered damaging winds and a few tornadoes are likely across the
Florida Panhandle into south Georgia through early evening. A strong
tornado or two is possible. Severe thunderstorms are also possible
across north Florida and overnight into the coastal Carolinas.

...FL Panhandle into southern GA...
The primary change with this outlook is to trim severe probabilities
and the general thunderstorm line in the wake of the convective band
running from south AL into the FL Panhandle and the northern Gulf of
Mexico. Otherwise, the previous forecast rationale remains valid.
With boundary-layer dewpoints increasing into the mid-upper 60s
dewpoints across the FL Panhandle and a very favorable wind profile
in place, supercells capable of producing tornadoes, strong wind
gusts, and isolated hail remain possible into the late
afternoon/early evening, with the threat eventually spreading into
southwest GA by early evening. See MCD 90 and the previous outlook
discussion below for more information. 

...North Florida...
Scattered thunderstorms have developed across north FL this
afternoon, in the vicinity of a surface boundary. A couple of
supercells may eventually evolve in this area, posting a threat of
all severe hazards. See MCD 92 for more information. 

...Coastal Carolinas...
A separate area of strong/locally severe thunderstorm development is
still expected across portions of the coastal Carolinas late
tonight. See the previous discussion below for more information.

..Dean.. 02/15/2021

.PREV DISCUSSION... /ISSUED 1030 AM CST Mon Feb 15 2021/

...FL Panhandle to south GA...
Upgraded to cat 3/ENH risk for the potential of a strong tornado or
two along with scattered damaging winds likely, a few of which may
be significant.

Scattered thunderstorms are underway from the surface cyclone that
is near the far southeast tip of LA into the north-central Gulf
along a sharp cold front. Additional convection may also develop
within the next couple hours ahead of this activity within
pre-frontal bands of confluence evident in visible satellite
imagery. As the surface cyclone deepens towards the AL/GA/FL border
area, the warm front should advance inland across the FL Panhandle
reaching southern GA by early evening. Mid to upper 60s F surface
dew points are expected in that regime, supporting a pronounced
gradient of MLCAPE from north to south, approaching 1500 J/kg along
the coast. Expect strengthening mid/upper winds supporting 50-65-kt
southwesterly effective-shear vectors, oriented just slightly
rightward of the main corridor of convective forcing with an
elongated mid/upper-level portion of the hodograph. The southern
fringe of a 45-60-kt LLJ will contribute to low-level hodograph
curvature with 200-400 m2/s2 effective SRH, greatest along the warm
front.

Pervasive stratus north of the warm front renders uncertainty over
the degree of tornado coverage as near-surface lapse rates may
remain less than ideal. However, the preceding favorable factors may
compensate and a conditional risk for a strong tornado or two is
apparent this afternoon. The tornado threat should subside some this
evening as the primary surface cyclone occludes across the western
portion of the Appalachians with the shortwave trough progressing
rapidly northeast away from the region.

...Coastal Carolinas...
Elevated thunderstorms should spread northeastward over interior
areas tonight, as a northward extension of the Gulf regime. A
separate, prefrontal low-level convergence zone is forecast to
support increasing thunderstorms tonight and affect coastal areas
through the end of the period.  A damaging-gust threat may develop
very near the coastline, where boundary-layer instability may be at
least marginally favorable, with tornado potential from any mature
supercell that can cross the coast. Farther northwestward, isolated
strong-severe gusts may penetrate the near-surface stable layer,
with potential diminishing with inland extent.

Along the coast, buoyancy will increase with proximity to the Gulf
Stream, where vertical heat/moisture fluxes will provide the most
sustained air mass modification. Forecast soundings still indicate
shallow near-surface stable layers at the bottom of the lifted layer
yielding surface- based effective-inflow parcels. However, vertical
shear will be favorable, with 45-55-kt effective-shear magnitudes
and effective SRH around 200-300 J/kg.

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