SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 PM CDT Tue Sep 24 2024
Valid 242000Z - 251200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
OHIO/TENNESSEE VALLEYS AND CENTRAL OKLAHOMA...
...SUMMARY...
Isolated to scattered severe thunderstorms remain possible through
the afternoon across portions of the Ohio and Tennessee Valleys into
the central/southern Appalachians. Severe storms will also be
possible across portions of Oklahoma this evening.
...20Z Update...
Severe probabilities were trimmed slightly eastward across portions
of the OH and TN Valleys, where the surface trough/wind shift has
passed by, reducing low-level convergence. Otherwise, multiple bands
of multicells and transient supercells will continue to pose a
threat for mainly damaging gusts through the evening, with a couple
instances of severe hail or even a tornado possible.
Despite the presence of mid-level clouds and lowering of surface
dewpoints over central OK, adequate boundary-layer heating is
contributing to continued destabilization, with 19Z mesoanalysis
already showing over 1000 J/kg MLCAPE in place. Continued surface
heating should support multicell/supercell development over the next
few hours, with severe hail and wind gusts the main concerns.
..Squitieri.. 09/24/2024
.PREV DISCUSSION... /ISSUED 1145 AM CDT Tue Sep 24 2024/
...Ohio and Tennessee Valleys to southern Appalachians...
Have spatially adjusted/expanded the Slight Risk based on
observational trends and somewhat stronger destabilization across
areas such as northern/middle Tennessee. Water-vapor imagery shows a
mid-level vorticity maximum moving across the middle Mississippi
Valley and into the Ohio Valley. A belt of moderate to strong
southwesterly 500-mb flow (25-50 kt) will overspread Kentucky and
the surrounding states. A surface low will migrate east-northeast
into southern Lower Michigan by early evening, where isolated severe
storms are possible, with a frontal zone extending south-southwest
from this low into the Mid South.
In the wake of early morning convection, modest cloud
breaks/destabilization is forecast with upwards of 750-2000 J/kg
MLCAPE from the southern Great Lakes into the southern Appalachians,
with the strongest destabilization expected across Tennessee into
southern Kentucky and possibly the western Carolinas pending the
timing/abatement of lingering cloud cover. Regionally, ample
deep-layer speed shear will aid in storm organization into organized
multicells and probably several supercells. Damaging winds will be
the most common hazard, but isolated large hail will be possible,
and some tornado risk may exist as well.
...Oklahoma/North Texas...
Have upgraded portions of central Oklahoma for what is expected to
be a semi-focused regional corridor of large hail potential late
this afternoon and early evening. The region will be influenced by
the immediate backside of a southeastward-moving upper-level trough
centered over the Lower Missouri Valley. A considerably
strengthening cyclonically curved belt of westerlies aloft will
influence Oklahoma, overspreading a relatively moist air mass, with
lower to some middle 60s F surface dewpoints likely to persist
through the diurnal heating/mixing cycle.
Near a deepening surface low and nearby triple point/warm front, at
least isolated storms are expected to develop as early as
mid-afternoon (3-4pm), becoming more probable with a greater
coverage through sunset. Overall buoyancy will not be robust, with
MLCAPE generally not expected to exceed 1000 J/kg later this
afternoon. However, this buoyancy, along with steep lapse rates and
robustly vertically veering wind profiles, accentuated by 35-45 kt
northwesterly mid/upper-level flow, should support initial
supercells capable of large hail (potentially golfball size), along
with some potential for damaging wind gusts.
These storms will persist generally southeastward through the
evening into southern/southeast Oklahoma, and probably north Texas
overnight. Overall intensity will tend to wane nocturnally after
sunset, but some severe hail/wind potential will probably linger,
particularly on the west/southwest flank of any evolving clusters of
storms, which will be increasingly elevated to the east of the warm
front.
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