SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0656 AM CST Fri Mar 11 2022
Valid 111300Z - 121200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MAINLY TONIGHT
OVER PARTS OF THE EASTERN FLORIDA PANHANDLE...NORTHWESTERN FLORIDA
AND SOUTHERN GEORGIA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM THE
CENTRAL GULF COAST AND NORTHERN FLORIDA TO THE CENTRAL
CAROLINAS...AND VERY LATE TONIGHT OVER EASTERN NORTH CAROLINA...
...SUMMARY...
Damaging wind, isolated hail, and a few tornadoes are possible
across the central and northeastern Gulf Coast to the Carolinas and
northern Florida. Isolated severe thunderstorms are possible during
the day, but the greatest threat appears to be late tonight into
Saturday morning.
...Synopsis...
A major trough is evident over central/southwestern North America at
this time, from a cyclone north of Hudson Bay across the Upper
Midwest, central Plains, Desert Southwest, and northern Baja. Two
primary shortwave troughs will become increasingly phased through
the period, contributing to the eastward progression of the
larger-scale, positively tilted trough:
1. A southern-stream perturbation apparent in moisture-channel
imagery over parts of southwestern CO, eastern AZ, Sonora, and
northern Baja. This feature should pivot eastward across NM today,
reaching OK, west TX and northern Chihuahua by 00Z. By 12Z, it
should merge with the amplified southern part of the feature below,
and reach the Mid-South and LA.
2. A northern-stream shortwave trough, currently over the MN/ON
Boundary Waters region, southwestward to SD. This perturbation is
expected to swivel to a less-positive tilt, and amplify, extending
from Lake Superior across WI/IA by 00Z. BY 12Z, this shortwave
trough should extend from northeastern ON to southern IL. and blend
with the southern-stream trough above, to form a progressive
synoptic-scale trough that will sweep eastward across the eastern
CONUS on day 2.
At the surface, 11Z analysis showed a synoptic cold front-over
northwestern OH, southern IN, central AR, through a weak frontal-
wave low over northeast TX, then arching across east-central/south-
central TX to northern Coahuila. This front is forecast to
intensify as the upper trough coalesces and moves eastward. By 00Z,
the front should extend across western portions of NY/PA,
southwestward over eastern TN and northern AL, to a developing
frontal-wave low over the southeastern MS/southern AL area, then
southwestward over the northwestern Gulf. That low is expected to
move rapidly northeastward tonight, reaching northern NC or
southeastern VA by 12Z tomorrow, with the cold front across the
eastern Carolinas, southeastern GA, the FL coastal bend, and
northeastern through southwestern Gulf. A quasistationary frontal
zone was drawn across extreme southern GA and the western FL
Panhandle, north of a series of aggregated outflow boundaries from
north-central FL to the northeastern/north-central Gulf. These
FL/GA boundaries may become more diffuse later today and especially
overnight, amidst a broad, rapidly intensifying, low-level,
warm-advection regime.
...Southeastern CONUS...
A complex severe-thunderstorm event with multiple rounds of activity
appears probable for the day-1 period, and will carry over past 12Z
into day 2 over eastern parts of the region. Some geographic
displacements and overlaps are likely between these convective
regimes, but enough mesoscale uncertainty lingers at this update
cycle not to get overly precise in introducing additional gaps or
holes to the severe-threat areas. The most spatial overlap still
appears to be over the eastern FL Panhandle/coastal bend,
northwestern FL and southern GA, where the cumulative of several
rounds of strong-severe thunderstorms yields the greatest total
full-period threat. Broadly speaking, the potential episodes are as
follows, in chronological order:
1. Northeast Gulf to northern FL today:
Multiple clusters of thunderstorms will form over the Gulf today and
move eastward to east-northeastward across the region -- a few
strong-severe with isolated supercells and organized multicells.
Severe weather should be isolated and sporadic, with damaging gusts,
occasional hail, and a couple tornadoes all possible. The most
favorable inflow-layer air mass will be along its eastern and
southern rim, with diurnally heated destabilization of the boundary
layer over northern FL ahead of ongoing convection, and optimized
surface theta-e over the northeastern Gulf. Despite potential for
baroclinic reinforcement by convective outflow, strengthening
ambient southwesterlies through much of the troposphere, as the
supper trough approaches, may contribute to a northward shift of the
convective boundary this afternoon into this evening, behind the
ongoing activity. 1000-1500 J/kg MLCAPE over northern FL along and
south of the older boundary, along with 35-45 kt effective-shear
magnitudes, will support some convective organization.
2. Southeastern parts of LA/MS to GA and Carolinas tonight:
This should become the main episode in terms of severe potential
over the longest area. Scattered thunderstorms are expected to form
along/ahead of the cold front, initially this evening in the
corridor from southeastern LA to southern AL, expanding both
northeastward and southwestward with time as the entire regime
shifts east. Convection should be mainly in quasi-linear and
clustered modes, but with a few discrete supercells possible. This
activity will sweep rapidly northeastward, offering damaging to
severe gusts and the potential for a few tornadoes.
Given the rapidly intensifying flow in midlevels, and in low levels
above the surface, vertical shear will increase substantially and
region-wide overnight. A swath of more-concentrated damaging-wind
potential may develop across parts of southeastern AL, western/
central GA, western/central SC and central NC late tonight, under
the fast-moving convection. However, uncertainties regarding
destabilization well inland -- north of the persistent convective
plume over the northeastern Gulf -- preclude boosting the
unconditional probabilities north of the existing "Enhanced" area at
this time. Forecast soundings suggest a slightly stable to neutral
near-surface layer that may mitigate downdraft momentum transfer
with severe wind somewhat -- but not eliminate it. The southern
part of this convective regime also should backbuild over the Gulf
and overtake the next one late tonight, likely from about 09Z
onward.
3. Northeast Gulf to northern FL/southern GA tonight:
Whether or not a respite develops between the daytime event over
this region and the overnight convection (progs are rather
inconsistent in that regard), the same plume of low-level lift
should support more thunderstorms overnight. As the western part of
this is overtaken by the prefrontal band tonight, severe potential
may maximize over the Enhanced area, with tornadoes and damaging
gusts the main concerns. Strengthening low-level mass response is
expected in the form of warm advection and moisture transport,
contributing to at least marginal low-level destabilization, despite
the longstanding presence of an antecedent convective boundary over
the northeastern Gulf. Any relative gaps would permit even more
destabilization inland.
3. Eastern NC, after 09Z:
Thunderstorms may move northward to northeastward across this region
just before the end of the period, in a plume of increasing low-
level lift and theta-e from adjoining Atlantic waters to the south.
Low-level and deep shear also will be strengthening rapidly during
this time frame, as a LLJ increases from the 40-60-kt range at 06Z
to at least 70-80 kt by 12Z. Thunderstorm coverage remains
uncertain, since instability will be weak (with MLCAPE 200-500
J/kg), and convective-scale forcing will be subtle in a regime
well-displaced from the primary frontal/convective boundaries.
Still, any sustained thunderstorms in this environment will pose a
threat for damaging gusts and tornadoes, given 50-60 kt effective-
shear magnitudes, 0-1-km shear around 30-45 kt, and enlarging
hodographs with time.
..Edwards/Kerr.. 03/11/2022
Read more
