SPC AC 061623

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1123 AM CDT Fri Apr 06 2018

   Valid 061630Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   THROUGH EARLY TONIGHT FROM NORTHEAST TX TO WEST CENTRAL MS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL AND NORTH
   TX TO THE LOWER MS VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK AREA...

   ...SUMMARY...
   Severe thunderstorms with damaging winds, occasional hail, and a few
   tornadoes, are expected this afternoon through tonight from north
   and central Texas eastward to the lower Mississippi Valley.

   ...Southern Plains to the lower MS Valley through tonight...
   A remnant lee cyclone now near Wichita Falls will move
   east-southeastward toward northeast TX and northwest LA by this
   evening, in advance of a series of low-amplitude mid-upper speed
   maxima.  The moist warm sector, characterized by boundary-layer
   dewpoints of 65-70 F, will continue to spread northward to a
   baroclinic zone from the Red River valley of TX/OK across southern
   AR/northern LA through the afternoon.  This southern baroclinic zone
   will be overtaken from northwest to southeast by a surge of arctic
   air now moving into the I-44 corridor, and this consolidated cold
   front will continue southeastward to south central/southeast TX and
   the lower MS Valley by the end of the period.

   Regional 12z soundings revealed an elevated mixed layer atop the
   moistening boundary layer across TX.  Daytime heating will boost
   MLCAPE to in excess of 3000 J/kg across TX, and closer to 1000-1500
   J/kg as far as west central MS by mid afternoon as the moisture
   spreads northward.  A few surface-based storms may form by this
   evening near the dryline-cold front triple point in TX, as well as
   southward along the dryline into central TX.  Here, the storm
   environment will favor supercells capable of producing isolated very
   large hail, especially with any storms that can remain discrete. 
   Otherwise, the main convective evolution is expected to be a gradual
   transition of the ongoing elevated convection across eastern OK/AR
   into surface-based convection along the consolidating cold front by
   mid afternoon.  These frontal storms will grow upscale fairly
   quickly into a squall line that will then surge southeastward this
   afternoon through tonight with the cold front.  The cap will be
   weaker with eastward extent from northeast TX across LA, and some
   convection could develop in the warm sector this afternoon. 
   Low-level shear/hodograph curvature will favor supercells with some
   conditional tornado threat, though there is uncertainty regarding
   the duration of any semi-discrete storms.  The more probable
   scenario will be for a couple of tornadoes with embedded supercells
   and/or QLCS mesovortices, along with damaging winds and isolated
   large hail this afternoon through early tonight.

   Buoyancy will slowly weaken overnight, and the convection should
   likewise weaken.  However, there will still be some threat for at
   least isolated damaging winds as far south as the I-10 corridor from
   southeast TX eastward to southern MS through early Saturday morning.

   ..Thompson/Peters.. 04/06/2018

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