SPC AC 271725

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1125 AM CST Sat Feb 27 2021

   Valid 281200Z - 011200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY AND OHIO
   VALLEY...

   ...SUMMARY...
   Isolated strong to severe thunderstorms appear possible from parts
   of Texas into the Ohio Valley on Sunday. Damaging wind gusts should
   be the main hazard, but some hail and a couple tornadoes may also
   occur.

   ...Southern Plains into the Lower Mississippi and Ohio Valleys...
   Multiple mid-level shortwave troughs will move eastward across the
   CONUS on Sunday. One such shortwave trough is forecast to advance
   from the northern Plains and Upper Midwest to the Great Lakes by
   Sunday evening. Another shortwave trough should develop slowly
   southeastward from the Great Basin to the Southwest, eventually
   closing off over AZ/NM late Sunday night. The primary surface low is
   expected to develop northeastward across the Upper Midwest/Great
   Lakes and into southern Ontario by Sunday evening, in tandem with
   the previously mentioned shortwave trough. A cold front extending
   southward from this low should be located over parts of the lower OH
   Valley into the Mid-South and southern Plains Sunday morning. This
   cold front will shift slowly southeastward through the period across
   these regions, and it will likely provide a focus for convection.

   A fairly broad swath of enhanced mid-level southwesterly winds
   should overlie the frontal zone, but stronger forcing associated
   with both shortwave troughs is likely to remain north of the warm
   sector. Still, forecast soundings from northeast TX into the lower
   MS Valley/Mid-South and continuing into parts of KY indicate a
   veering and strengthening wind profile with height through mid
   levels. Upwards of 50-60+ kt of effective bulk shear appears likely,
   which is clearly sufficient for organized storms, including
   supercells. However, two potentially limiting factors remain
   apparent. One is the orientation of the front nearly parallel with
   the southwesterly mid-level flow. Tendency may be for storms to form
   along the front and then get quickly undercut while becoming
   elevated. The other limitation may be generally weak low/mid-level
   lapse rates and related modest instability. Even so, the presence of
   surface dewpoints generally in the 62-68 F range coupled with some
   diurnal heating south of the front should support MLCAPE around
   250-1000 J/kg by Sunday afternoon.

   Current expectations are for mainly elevated storms to be ongoing
   across parts of the lower OH Valley Sunday morning in a strong
   low-level warm advection regime. Additional convective development
   appears likely along much of the length of the cold front by late
   Sunday morning or early afternoon. Short bowing line segments may
   pose an isolated damaging wind threat as they move
   east-northeastward. Even though low-level flow should tend to veer
   to southwesterly across much of the warm sector through the day,
   enough low-level shear may remain to pose a threat for a couple
   tornadoes with either semi-discrete storms or circulations embedded
   within the line segments. Eventually, this isolated severe threat
   should wane across the lower MS Valley and TN Valley Sunday evening
   as storms become mainly elevated behind the front. Finally, some
   hail threat may exist with elevated storms both Sunday morning and
   Sunday night across parts of TX into the ArkLaTex vicinity.
   Mid-level lapse rates should be modestly steepened across this
   region in advance of the shortwave trough over the Southwest, and
   deep-layer shear will likely be rather strong and uni-directional,
   potentially supporting elevated supercells.

   ..Gleason.. 02/27/2021

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