SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0633 AM CST Fri Feb 16 2024
Valid 161300Z - 171200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
No areas of organized severe thunderstorms are forecast over the
conterminous U.S.
...Synopsis...
A highly amplified mid/upper-level pattern will persist over the
CONUS today, as an initial high-latitude omega configuration over
western Canada evolves into a full-latitude, open-wave, synoptic
ridge. That ridge will extend southward over the western U.S. as
well. The eastern portion of a shortwave trough -- initially over
the northern Rockies -- will break away from the remainder of the
height weakness footing the omega pattern and reach parts of
southwestern WY, southern ID and northern UT by 00Z. The trough
then should dig southeastward to parts of CO/UT by the end of the
period. As that occurs, a weaker, downstream perturbation --
evident in moisture-channel imagery near an axis from HLC-AMA-INK --
will weaken gradually as it moves eastward across OK and AR,
reaching the lower Ohio Valley and western TN by 00Z. What is left
of this feature should accelerate eastward over the central
Appalachians by 12Z tomorrow.
At the surface, 11Z analysis showed a frontal-wave low near FDR,
with wavy warm front across central parts of OK/AR to northern MS.
An initial/weak cold front was drawn from the low southwestward over
southern NM and an Arctic front across the southeastern TX Panhandle
to northeastern NM. These fronts should merge through the day,
while the low ripples rapidly east-northeastward along the warm
front. The low should reach south-central/southeastern KY by 00Z,
with trailing cold front across middle TN, northern MS, the Arklatex
region, and south-central TX. By 12Z, the low should move offshore
from Hampton Roads, with cold front over central NC, north-central
GA, south-central AL, to parts of the north-central/northwestern
Gulf.
...AR/Mid-South...
Scattered thunderstorms are expected to form this afternoon into
evening over AR, along/ahead of the surface cold front, then shift
eastward while backbuilding southward. A resultant band of
thunderstorms should cross parts of western TN, northern MS and
northern LA before weakening substantially late this evening. The
strongest cells within the band -- especially early in the
convective cycle when discrete storms still are possible -- may
produce hail approaching severe limits and strong gusts. Severe
potential still appears too low and conditional for a categorical
risk area; however, an isolated, marginally severe hail report or
damaging subsevere gust cannot be ruled out.
Surface dewpoints in the 50s F already extend from the Gulf into the
warm sector across parts of this region, and should remain in place
as moist advection offsets any diurnal mixing. The return-flow
regime will remain incompletely modified, so that the convective
plume will outrun already modest moisture this evening while
diabatic cooling takes hold. Time series of forecast soundings
depict two simultaneous processes:
1. Effective-inflow parcels becoming surface-based this afternoon,
in a narrow prefrontal corridor, due to warm advection and
cloud-slowed diurnal surface warming. This should contribute to
peak preconvective MLCAPE in the 300-800 J/kg range.
2. Veering of surface winds with time, reducing hodograph size,
low-level SRH and low-level bulk shear. Deep shear will be marginal
to favorable, even with veering of low-level flow. 0-6-km shear
magnitudes in the 45-55-kt range are expected. However, effective-
shear magnitudes are only around 1/2-2/3 that range, because the
low-topped/compressed nature of the buoyant layer shunts the upper
reaches of the calculation to below the strongest mid/upper winds.
With the favorable kinematic and thermodynamic factors trending
oppositely through the afternoon, and the regime already being
somewhat moisture/buoyancy-starved, unconditional probabilities will
be held below MRGL categorical levels for the time being.
..Edwards.. 02/16/2024
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