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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