SPC AC 270536

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1236 AM CDT Wed May 27 2020

   Valid 281200Z - 291200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST
   TX/TX HILL COUNTRY EASTWARD INTO THE SOUTHEAST AND LOWER OH/TN
   VALLEY AND ALSO OVER PORTIONS OF THE MID-ATLANTIC...

   ...SUMMARY...
   Isolated severe thunderstorms are possible from southwest Texas
   eastward/northeastward into the Southeast and Tennessee Valley
   Thursday afternoon through Thursday evening. Isolated severe storms
   are also possible across portions of the Mid-Atlantic.

   ...Southern Plains through Lower MS Valley into the Southeast and TN
   Valley...
   An upper cyclone, initially centered over the Ozark Plateau, is
   forecast to progress northeastward into the lower OH Valley
   Thursday. A moist and moderately unstable air mass will be in place
   from the southern Plains eastward/northeastward over much of the
   eastern CONUS. Widespread thunderstorm development is anticipated as
   the upper cyclone and its attendant surface trough interact with
   this air mass. Moderately enhanced low/mid-level flow will exist
   throughout the southern and eastern periphery of this cyclone,
   resulting in a broad area where vertical shear could support
   stronger, more organized updrafts. There is also the possibility for
   one or more convectively enhanced vorticity maxima to be rotating
   through this upper cyclone, which could augment vertical shear and
   resulting severe potential.

   Poor lapse rates and the resulting marginal buoyancy should limit
   the intensity of any severe risk while also tempering overall severe
   coverage. Damaging wind gusts will be the primary severe threat
   across much of the region. The only exception is across portions of
   southwest TX and the TX Hill Country. Here, steeper lapse rates will
   contribute to stronger buoyancy, which could support updrafts robust
   enough to produce large hail. However, the severe threat is more
   conditional across this region, with uncertainty regarding air mass
   recovery behind the previous day's storms, as well as uncertainty
   regarding the extent of boundary-layer mixing.

   For deep south TX, primary severe risk is expected early in the
   period when some of guidance suggests a decaying MCS will move
   through the region. Variability within the guidance and general low
   predictability of MCS evolution merits limiting severe probabilities
   to 5% for this outlook.

   ...Mid-Atlantic...
   Remnant tropical wave is expected to progress northward out of the
   Mid-Atlantic and into the Northeast early in the period, but ample
   moisture (i.e. PW values near 2") will remain over the Mid-Atlantic
   in its wake. Daytime heating amidst this moisture will likely result
   in numerous afternoon thunderstorms. Weak shear will preclude any
   organized severe risk, but isolated water-loaded downdrafts could
   resulting damaging downburst winds.

   ...Upper Midwest...
   A shortwave trough is expected to move from the Canadian Prairie
   Provinces through western Ontario and the Upper Midwest on Thursday.
   An associated surface low is forecast to move through western
   Ontario while an attendant cold front moves through the Upper
   Midwest. Guidance varies on the amount of destabilization that
   precedes the front across central/southern WI and adjacent portions
   of northwest IA and northern IL, but thunderstorms are probable.
   Weak vertical shear will limit overall severe potential, but
   instability will likely be high enough to support a few stronger
   storms.

   ..Mosier.. 05/27/2020

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