Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1247 AM CDT Thu Apr 11 2024
Valid 111200Z - 121200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER OHIO RIVER VALLEY...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE OHIO RIVER VALLEY AND NORTHERN FLORIDA TO SOUTHERN GEORGIA...
...SUMMARY...
Severe thunderstorms with a few tornadoes, scattered damaging winds,
and isolated large hail are possible across the upper Ohio River
Valley and parts of the Appalachians this afternoon. Scattered
damaging winds and a couple tornadoes will also be possible across
southeast Georgia into northern Florida, mainly this morning through
early afternoon.
...Synopsis...
04 UTC surface observations depict a diffuse surface low over the
lower MS River Valley. This low is forecast to deepen over the next
24 hours as it lifts northward into the OH Valley/Great Lakes region
in tandem with the phasing of an amplified upper-level trough over
the MS Valley with an approaching upstream perturbation. A surface
cold front currently draped across southeast LA will surge to the
east/northeast as the low deepens, and should act to focus
thunderstorm development through the late morning and afternoon
hours across both the upper OH Valley and Southeast.
...Upper OH River Valley...
Recent 925/850 mb analyses and surface observations show a
consolidating warm frontal zone draped from the surface low over the
lower MS Valley into the upper OH River Valley. The surface low will
deepen along this corridor amid a combination of strong height falls
and ascent within the left-exit region of a mid-level jet. A plume
of low to mid-60s dewpoints will advect northward with the deepening
low, establishing a focused warm sector ahead of the approaching
cold front by early afternoon across parts of KY, OH, and WV. The
current expectation is for sufficient destabilization within the
warm sector to support surface-based convection by the 18-21 UTC
time frame. A combination of strong synoptic-scale ascent and 40-50
knot deep-layer shear vectors off the cold front should promote a
mix of discrete cells and semi-discrete clusters - including the
potential for a few supercells. Increasing southeasterly winds
through the lowest 1-2 km should yield effective SRH values between
150-300 m2/s2, which will support a tornado threat with the more
robust/organized cells as well as a wind threat with more organized
clusters. This threat appears greatest across southeast OH into
western WV where latest guidance continues to show a focused
convective signal. Further to the east into parts of northwest VA, a
somewhat weaker convective signal is noted in most CAM guidance, but
50-knot flow in the lowest 2 km will likely pose a substantial wind
threat with any storms that can mature. Risk probabilities have been
expanded into this region to account for this potential.
That said, this scenario appears to be conditional on achieving
sufficient low-level warming within the warm sector. While an
extensive dry slot is noted in water-vapor imagery across the
Mid-South into central IN, the low/mid-level warm advection regime
is maintaining mid-level stratus across the region with most ASOS
stations reporting overcast skies and ceilings near 6 kft. It is
unclear how much clearing will occur through early afternoon given
persistent ascent, and a 10 F spread in afternoon high temperatures
is noted across OH/WV in recent ensemble guidance. Based on forecast
soundings, surface temperatures in the upper 60s may be required to
realize 500+ J/kg SBCAPE with minimal inhibition. The median of the
temperature distribution appears to reside in the upper 60s, but
SBCAPE may still only reach 500-1000 J/kg per ensemble
distributions.
...Florida/Georgia...
Lingering thunderstorms associated with overnight convection will
likely be ongoing across the FL Panhandle at 12 UTC. This activity
should become consolidated into a more organized line as the cold
front pushes east through the morning across southern GA and
northern FL. Poor lapse rates sampled by 00 UTC soundings across
central/northern FL will limit buoyancy despite mid/upper 60s
dewpoints. However, strong kinematic fields should be in place as a
mid-level jet max passes overhead. Forecast hodographs suggest
effective bulk shear values around 50-55 knots will be common, and
low-level SRH may approach 150 m2/s2 along/ahead of the line. The
severe risk will likely be modulated by the degree of diurnal
destabilization that can occur ahead of the line, but stronger
cells/segments may pose a severe wind/tornado risk given the
favorable wind profiles. This risk may peak by late morning before
the line begins to move offshore and forcing for ascent gradually
abates by late afternoon as the synoptic low lifts well to the
north.
..Moore/Darrow.. 04/11/2024
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