SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0757 AM CDT Thu Mar 14 2024
Valid 141300Z - 151200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF EASTERN OKLAHOMA...ARKANSAS...EXTREME NORTHEAST TEXAS...AND
SOUTHERN MISSOURI...
...SUMMARY...
Tornadoes, large to very large hail, and strong to locally severe
thunderstorm gusts are expected from parts of north-central Texas
into the Midwest and Mid-South. The greatest overall severe threat
still appears to be across eastern Oklahoma into Arkansas and
southern Missouri.
...Synopsis...
In mid/upper levels, the pattern will slow considerably and become
blocky over the western CONUS, as a closed cyclone continues to
retrograde south-southwestward across the southern Great Basin and
southern CA. The associated/cut-off 500-mb low should stall near
the Imperial Valley by 12Z tomorrow, with troughing southward over
Baja and northeastward over southwestern WY. A broad swath of
southwest flow aloft will extend downstream of the cyclone, across
the southern Plains, lower/mid Mississippi Valley and lower Ohio
Valley. Weak synoptic-scale height rises are expected over much of
OK, AR, east/north TX, and LA, in response to the cyclonic
retrogression farther west.
At the surface, 11Z analysis showed a low near TOP with cold front
southwestward across northwestern OK to the TX Panhandle, and warm
front over northern portions of MO/IL/IN to central OH. A dryline
was drawn from central OK across west-central TX. The dryline is
expected to move only slightly eastward through the day, being
positioned over central/east-central to south-central OK and north-
central/central TX during mid/late afternoon. A combination of the
cold front and convective outflow will overtake the dryline over MO
and OK by late afternoon and evening, and the front should catch the
dryline over north TX overnight. Meanwhile, a sequence of
convective outflows -- already underway across parts of the Midwest
and forecast to continue through the day -- will shunt the effective
baroclinic zone and best regional convective foci south of the
synoptic warm-frontal position.
...Ozarks to north TX and Mid-South...
Scattered thunderstorms should develop as early as midday along and
east of the OK/TX dryline, and increase in coverage/intensity
through the evening, while shifting eastward into AR, perhaps
reaching parts of the Mid-South and Tennessee Valley regions
overnight. Supercells with tornadoes (some strong), locally very
large/destructive hail, and severe gusts will be possible this
afternoon into early evening. Activity should evolve into one or
two dominant quasi-linear segments with the threat trending more
toward wind and sporadic QLCS/embedded tornadoes with time this
evening and overnight.
Continued theta-e advection east of the dryline, amidst strong
diurnal heating, will erode MLCINH, which already did not appear
particularly strong in the 12Z OUN sounding. Modified RAOBs and
forecast soundings over eastern OK this afternoon suggest peak/
preconvective MLCAPE reaching the 2500-3000 J/kg range. Increasing
inflow-layer moisture beneath favorable deep shear (effective-shear
magnitudes 45-55 kt) yield hail over 3 inches in diameter when 2D
hail models and historical analogs are applied. The duration of the
threat, as well as the potential for tornadoes once hodographs
enlarge greatly in late afternoon/evening, will depend on the number
of relatively discrete supercells remaining. That is uncertain,
given a substantial component of deep-layer flow parallel to the
likely corridor of greatest forcing, which suggest a transition to
messier convective modes. However, at least a few tornadoes are
possible, including those with strong damage potential. Upscale
evolution to an MCS appears possible this evening into tonight,
spreading toward the Mid-South/Tennessee Valley regions.
A separate area of convection also may develop this afternoon into
early evening east of the modest EML plume, over parts of the Mid-
South/Delta region. The environment will be characterized by rich
low-level moisture (dewpoints increasing into the upper 60s to low
70s F), subtle mass confluence/convergence, and weak CINH. While
low-level flow/shear will be modest, enough mid/upper-level flow
will spread over the area to support a mix of multicell and
supercell modes, with damaging gusts, large hail possible, and a
marginal tornado threat. Forecast soundings reasonably depict a
deep troposphere occupied by MLCAPE increasing into the 2000-3000
J/kg range, and around 30-40 kt effective-shear magnitudes.
Ultimately, the main area of convection from the west and northwest
also may shift into this area overnight, overtaking any remaining
warm-sector activity and bringing severe probabilities as well.
...Midwest/Ohio Valley region...
Bands of thunderstorms with trailing, progressive outflows are
ongoing across portions of IL/MO. This activity should continue
offering sporadic severe gusts and isolated potential for an
embedded tornado or two, while moving rapidly east-northeastward
this morning. Severe-gust and tornado threats may focus best along
the warm front and leading outflow boundary. Those boundaries are
where low-level convergence/vorticity will be maximized. However,
severe potential also may be tempered regionally by the early-
morning instability minimum in the boundary layer. See SPC severe
thunderstorm watches 39-40 and related mesoscale discussions for
near-term details. Some re-intensification of the combined complex
may occur in parts of IN and perhaps KY today, as it encounters a
plume of diurnal and warm-advection-related destabilization, before
outrunning that plume.
Farther west and southwest across portions of eastern/southeastern
MO and up the lower Ohio Valley, a conditionally concerning threat
is apparent for tornadoes, large to very large hail and severe wind
from another potential round of convection this afternoon and
evening. Where the environment is undisturbed by (or can recover at
least mostly from) morning convection, strong deep-layer shear and
favorable moisture/destabilization will support potential for long-
lasting supercells and bowing clusters. Along and within an ill-
defined distance north of the residual, diurnally destabilized
outflow boundary, enlarged low-level hodographs and maximized
boundary-layer shear/vorticity should concentrate tornado potential.
At this time, however, with
1. Outflow still being newly produced, and
2. Its depth/character not well-resolved yet by higher-resolution
convective guidance, mesoscale uncertainties over the position and
character of the boundary remain too great to assign larger
unconditional risk at this point. A focused corridor of enhanced-
level probabilities may need to be introduced once the timing and
location of the near-boundary threat become clearer.
..Edwards/Dean.. 03/14/2024
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