SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0743 AM CDT Wed Mar 16 2022
Valid 161300Z - 171200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
FLORIDA TO PARTS OF SOUTH CAROLINA...
...SUMMARY...
Isolated severe thunderstorms will be possible across parts of the
Southeast today. Large hail should be the main threat, with marginal
potential for damaging gusts or a tornado.
...Synopsis...
In mid/upper levels, a progressive pattern over the CONUS features
three primary, convectively influential perturbations:
1. A closed cyclone, initially centered over the MS/AL border area,
along a height trough extending from central KY to the central Gulf.
The low and trough are forecast to weaken slightly -- but still
maintain a closed circulation, while moving east-northeastward
across the Southeast through the period. By 12Z tomorrow, the
500-mb low should be located near CLT, with trough southward across
SC and just offshore GA.
2. A southern-stream shortwave trough initially evident in
moisture-channel imagery over portions of NV/CA. This feature
should amplify and move east-southeastward across the Great Basin
today. Associated DCVA/destabilization and cooling aloft will
combine with diurnally warmed boundary layers to support isolated
thunderstorm potential over parts of the Great Basin and Four
Corners region.
3. A northern-stream perturbation -- currently located over the
interior Pacific Northwest. This feature also should amplify and
move east-southeastward through the period. Some phasing with the
southern-stream trough may occur late tonight. In the meantime,
associated steepening of low/middle-level lapse rates will spread
across parts of MT, with weak but sufficient low/middle-level
moisture to support isolated thunderstorms.
At the surface, 11Z analysis showed a broad, poorly defined
low-level cyclone centered near SEM. An occluded front arched from
the low across southeastern AL, to a triple point estimated between
TLH-PFN. A cold front extended from there southward then
southwestward over the eastern and central Gulf. A warm front was
drawn across northern FL, and was poorly defined over land with
residual/rain-cooled air on both sides. The front was sharper across
coastal waters of GA, to just offshore from SC and southeastern NC.
The warm front will move northward across southern/central portions
of both GA/SC today, perhaps into extreme southern NC tonight. An
outflow boundary from previous night's activity lingers
quasistationary over central FL, and should drift northward through
the afternoon.
By 00Z, the broad low-level cyclone will cover much of AL/GA,
tilting slightly northward with height into the midlevels. The cold
front should extend across south-central GA, north-central/west-
central FL, and the eastern/south-central Gulf. The area of surface
low pressure may consolidate somewhat over the eastern NC tonight,
with the 12Z frontal position from there southward over Atlantic
waters across parts of south FL.
...Southeast...
Isolated to scattered thunderstorms are expected to form today ahead
of the surface cold front, in a broadly arc-shaped corridor from
south-central/central FL across the JAX/SAV areas near the Atlantic
Coast, to portions of eastern GA and southern/central SC. The main
concern will be large hail, especially from any supercells that
develop, with isolated damaging gusts and a tornado or two also
possible. Without substantial/ongoing convection across much of the
region, especially across the FL Peninsula, ample diabatic
destabilization is expected by early/mid afternoon, in a suitably
moist environment with shear favorable for a few supercells.
Significant (2+ inch diameter) hail also may occur in central FL,
given:
1. Enough deep shear for supercells (effective-shear magnitudes
around 40-45 kt) -- especially near the remnant outflow boundary --
supporting potential for sustained, storm-scale rotation to augment
updraft intensity;
2. Ample inflow-layer water content to foster hail growth, with
surface dew points commonly in the mid 60s to low 70s F by expected
storm-maturation time in early/mid afternoon;
3. A "top-heavy" buoyant profile well into favorable ice-growth
layers, with diabatic heating and aforementioned moisture beneath
steep midlevel lapse rates (leading to MLCAPE around 1500 J/kg,
locally near 2000 J/kg);
4. The appearance of a few historic analogs for significant hail in
several forecast soundings in the area.
The main remaining question is the extent supercells can remain
relatively discrete long enough to produce very large hail. Still,
given the favorable environment, a 10%/hatched "sig-hail" area has
been introduced.
Isolated, marginal severe potential will extend westward from the
northern part of the 15% hail area across GA and parts of AL,
deeper into the midlevel core region of the mid/upper cyclone. In
those areas, the coldest air aloft will be present, but with weak
winds aloft limiting vertical shear. Isolated severe also may occur
from predominantly multicellular thunderstorms southward over parts
of south FL, where favorable moisture/buoyancy will be present, but
with weaker low-level flow, smaller hodographs and less low-level
shear than over central parts of the peninsula. Marginal severe
potential also may develop this afternoon through tonight over parts
of southern/eastern NC, but with modest instability aloft (MUCAPE
around 300-800 J/kg) and weak low-level lapse rates as limiting
factors.
..Edwards/Kerr.. 03/16/2022
Read more
