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ACUS01 KWNS 110548

SWODY1

SPC AC 110547



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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