SPC AC 131956
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Thu Mar 13 2025
Valid 132000Z - 141200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
ALABAMA...WESTERN FLORIDA...AND SOUTHERN GEORGIA...
...SUMMARY...
Isolated strong to severe thunderstorms capable of producing hail
and locally damaging gusts are possible from parts of Alabama, into
southwest Georgia, and the Florida Panhandle this afternoon and
early evening.
...20z Update...
Minimal changes were made to the MRGL risk area over parts of the
Southeast, mainly to trim the western extent. Mid-level subsidence
behind the weakening vort max over parts of MS/TN will tend to limit
thunderstorm potential to the west through the remainder of the
afternoon. To the east, increasing low-level moisture and steep
lapse rates will support isolated thunderstorms with a risk for hail
and sporadic damaging gusts.
Elsewhere, strong mid-level height falls are expected over the
western US as a powerful upper trough approaches. A few elevated
thunderstorms are possible within warm air advection over the Upper
Midwest ahead of shallow returning surface moisture. To the west,
cool mid-level temperatures overspreading meager low-level moisture
will also support isolated thunderstorm chances over a broad area
from the Desert Southwest to the Rockies. Somewhat stronger,
low-topped convection is possible along the cold front from southern
AZ into far western NM this evening and tonight. Given the strength
of the wind fields aloft, a few severe gusts will be possible.
Though, the very limited buoyancy should limit the severe threat.
See the previous discussion for more info.
..Lyons.. 03/13/2025
.PREV DISCUSSION... /ISSUED 1122 AM CDT Thu Mar 13 2025/
...Southeast...
A mid-level vorticity maximum over the Mid-South late this morning
will become less well defined as it moves slowly eastward across the
TN Valley and Southeast through the period. Stronger mid-level flow
is expected to remain over southern/coastal portions of the
Southeast today. But, cold mid-level temperatures (around -18 to -21
C at 500 mb per 12Z regional soundings) in conjunction with filtered
daytime heating and modest low-level moistening will support weak
destabilization from parts of AL into southwest GA, and the FL
Panhandle. Current expectations are for isolated to scattered
thunderstorms to develop across these areas through the afternoon,
as modest ascent with the weakening mid-level trough moves through.
Most guidance suggests that greater convective coverage may occur
over parts of southeast AL into southwest GA and perhaps the FL
Panhandle, in closer proximity to greater low-level moisture and the
mid-level jet. With modest to sufficient deep-layer shear, clusters
to marginal supercell structures could pose an isolated threat for
both severe hail and damaging winds this afternoon through early
evening. See Mesoscale Discussion 167 for additional details on
convective development and evolution through 20Z.
...Southern Arizona...
A cold front will move eastward across southern AZ today, as an
upper trough progresses over the Southwest. Showers and
thunderstorms are expected to spread across this region in tandem
with the front. Winds aloft will be quite strong, as an 80-100 kt
mid/upper-level jet max digs southward along/near the international
border. Some higher momentum flow may mix to the surface, and a gust
could approach severe limits within low-topped convection. However,
the weak thermodynamic profile would suggest the severe threat will
remain low.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
SPC AC 131728
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Thu Mar 13 2025
Valid 141200Z - 151200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN SOUTHEAST
IA...EASTERN MO...IL...FAR WESTERN KY/NORTHWEST TN/NORTHEAST AR...
...SUMMARY...
A regional outbreak of severe storms is likely over the
Lower/Mid-Missouri/Mississippi Valleys and Lower Ohio Valley late
Friday afternoon into Saturday morning. Tornadoes, several of which
could be strong, widespread damaging winds with gusts from 70 to 90
mph, and scattered large hail up to baseball size will be possible.
...Synopsis...
Primary change this outlook cycle has been to mainly expand
MRGL/SLGT/ENH damaging wind probabilities west to north in the
Lower/Mid-MO Valley. No change to the level 4/MDT risk with greater
uncertainty over the southern extent of widespread damaging wind
potential into the Mid-South, but where strong tornado potential
persists.
...Lower/Mid-MO, Mid-MS, and Lower OH Valleys...
A powerful shortwave trough will amplify from the southern High
Plains into the Upper MS Valley. This will induce further deepening
of an intense surface cyclone across the central Great Plains to the
Mid-MO Valley. Initial surface-based thunderstorm development is
expected by early to mid-afternoon along the northwest periphery of
a modified moisture plume emanating north from the South-Central
States. Well-mixed, inverted-v thermodynamic profiles will support
downward momentum transport in the left-exit region of an intense
700-mb jet curling across the Ozarks to the Mid-MS Valley. This
should yield a rapidly progressing QLCS from the Lower to Mid-MO
Valley across much of the Mid-MS Valley into Friday evening, with
semi-discrete supercells trailing to the southeast portion of the
convective plume. Given the fast low to mid-level flow regime,
embedded gusts from 60-80 kts should be common along with a
QLCS/embedded supercell tornado threat. The latter will be greater
with southeast extent where a ribbon of somewhat richer low-level
moisture should reach the Mid-MS Valley. Convection should tend to
weaken overnight more quickly on the north end of the outlook area
as it outpaces the confined surface-based instability plume. But
some overnight damaging wind/tornado potential should persist across
the Lower OH Valley.
...Mid-South to Lower MS and TN Valleys...
South of the QLCS regime, forecast confidence in sustaining deep
convection lowers with southern extent. Persistent southerly
low-level flow will bring mid to upper 60s F dewpoints northward
across the region by Friday evening/night. Forecast soundings
indicate rather favorable thermodynamic and kinematic profiles,
conditionally supporting intense and long-track supercells. Neutral
to weak mid-level height falls are expected, with the strong
low-level jet tending to shift north/east of the Lower MS Valley
overnight. This suggests forcing mechanisms will be modest, which is
likely behind guidance spread with the depiction of deep convection
during the evening and overnight.
A few broken to semi-discrete supercells appear most probable in the
Mid-South, posing a risk for strong tornadoes, significant damaging
wind gusts, and very large hail. These threats appear more
conditional farther south/east in the Lower MS and TN Valleys.
..Grams.. 03/13/2025
WUUS02 PTSDY2
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
SPC AC 131930
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 PM CDT Thu Mar 13 2025
Valid 151200Z - 161200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN EASTERN
LA...MS...AND AL...
...SUMMARY...
A severe weather outbreak is expected on Saturday across the central
Gulf Coast States and Deep South into the Tennessee Valley. Numerous
significant tornadoes are possible on Saturday afternoon and
evening, centered on eastern Louisiana, Mississippi, and Alabama.
Widespread damaging wind swaths and scattered large hail are likely.
...Central Gulf Coast/Deep South/TN Valley...
Primary change is to expand level 4-MDT north in AL and all
categories west in the tight gradient of severe potential from the
Sabine to Lower MS Valleys. A particularly volatile scenario for
destructive severe remains evident during the afternoon to evening
on Saturday centered on the level 4-MDT risk region.
In the wake of the vigorous shortwave trough and very deep surface
cyclone crossing the North-Central States on D2, a broad upper
trough will linger across the southern Great Plains. An intense
mid-level jetlet, in excess of 100 kts at 500-mb, should eject
through the basal portion of this trough in south TX on Saturday
afternoon. This will induce secondary cyclogenesis along the
slow-moving baroclinic zone from the Ark-La-Tex to the central Great
Lakes. Another day of air mass modification ahead of this wave will
yield a pronounced plume of rich northwest Gulf moisture that should
be pristine across southeast LA into central MS through late
morning. As mid-level height falls overspread the diurnally warming
air mass, increasing convective development is expected along the
deepening baroclinic zone, as well as residual outflows to its
northeast in the TN Valley from prior late D2 convection.
Steep mid-level lapse rates atop the richly moist boundary layer
should yield at least moderate MLCAPE across the Lower MS Valley.
Vertically veering wind profiles with strong anvil-level divergence
amid the favorable instability should support robust updrafts and
intense supercells. Low-level shear will strengthen during the
afternoon and evening, setting the stage for a severe-weather
outbreak including significant tornadoes, damaging gusts, and large
hail. A pronounced dropoff in severe may be realized with northward
extent across the TN Valley as an emerging band and/or highly
organized line outpaces the rich Gulf air. Despite weaker
instability with eastern extent into GA/SC, the intense wind fields
may sustain damaging wind and embedded tornado potential well into
the overnight.
...OH Valley to Lower Great Lakes...
Forecast confidence is low with regard to severe potential north of
the TN Valley. Weakening late D2 convection should be in a decaying
process at 12Z Saturday. Much of the region will then be in between
waves until late afternoon. Guidance differs on the degree of
diurnal destabilization ahead of the deepening surface cyclone that
should track north-northeast from the Ark-La-Tex. It is plausible
that widespread Mid/Deep South to TN Valley convection during the
day Saturday will temper the northward extent of instability by
Saturday evening/night within a predominately meridional deep-layer
wind profile. As such, the overall severe risk appears conditional,
but given the fast flow regime, potential for damaging winds and
perhaps a few tornadoes may be realized.
..Grams.. 03/13/2025
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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