SPC AC 080600

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Thu Apr 08 2021

   Valid 091200Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR
   NORTH-CENTRAL TEXAS EASTWARD INTO NORTHERN LOUISIANA AND
   MISSISSIPPI...

   ...SUMMARY...
   Scattered severe thunderstorms are forecast on Friday from parts of
   Oklahoma and Texas eastward through the lower Mississippi Valley. 
   Large to giant hail is possible across parts of Texas, and a swath
   of damaging gusts and several tornadoes are possible from Texas east
   into Mississippi.

   ...Synopsis...
   A mid-level low will weaken and meander northward over the western
   Great Lakes.  A more potent, upstream mid-level trough will move
   from WY southeastward into eastern KS/OK by early Saturday morning. 
   A lower-amplitude disturbance in the southern stream will move
   eastward from southwest Texas into the lower MS Valley.  In the low
   levels, an area of low pressure over western north-central TX will
   develop eastward and reach the AR/MS/TN vicinity by daybreak
   Saturday.  A dryline will extend southward near the I-35 corridor in
   north-central TX.  A residual front will advance northward across
   much of AR and western TN.

   ...Southern Great Plains...
   A seasonably moist/unstable airmass sampled by Wednesday evening
   raobs along the TX Gulf Coast, and an elevated mixed layer, will
   overlap and result in a very unstable airmass developing across TX
   east of the dryline with 3000 J/kg MLCAPE forecast.  Rather cold 500
   mb temperatures (-15 to -16 deg C) will result in very large CAPE in
   the -10 to -30 deg C layer.  A strong capping inversion will weaken
   with localized erosion of the cap by the late afternoon via strong
   heating, convergence near the dryline, and the aforementioned
   disturbance moving east across TX.  Explosive updraft growth is
   expected with isolated to widely scattered storms developing from
   southern OK southward into east-central TX.  A veering and
   increasing wind profile with height will strongly favor discrete
   supercells, before additional storm development occurs during the
   evening as storms move east into the Arklatex.  In addition to hail
   and a tornado risk, the threat for damaging gusts will probably
   increase during the evening as this activity moves east into the
   Arklatex.  

   ---model discussion---
   The 08/00z and 07/18z NAM runs exhibit a too-cool bias with surface
   temperatures east of the dryline across north-central TX (low to mid
   70s near DFW metro), specifically near the I-35 corridor.  Moreover,
   it is likely strong heating will occur across central and north TX
   during the day with temperatures at least 90 F west of the dryline
   and into the middle 80s to the east in the warm sector.  As a
   result, ARW-based convection-allowing models (based on the parent
   ARW model) are likely misrepresenting thunderstorm potential across
   TX during the 21z-03z period.  Conversely, the 08/00z and 07/18z GFS
   runs are showing excessive boundary-layer mixing and a too-warm bias
   across north-central TX with the dryline likely displaced too far
   east compared to its likely position near I-35 by late afternoon. 
   The 07/12z ECMWF appears superior to the NAM/GFS in this regard with
   adequate boundary-layer mixing implied by the warmer surface
   temperatures (mid 80s F).  This forecast across the southern Great
   Plains coincides with model output similar to the ECWMF in recent
   model runs.

   ...Northern Gulf Coast states...
   A complex forecast is seemingly evident for this region and
   concerning mainly the after-dark severe threat expected to develop
   from LA eastward into MS/AL.  Models indicate a moisture-rich
   boundary layer beneath steep lapse rates will be present during the
   day.  Despite the presence of a capping inversion, isolated to
   widely scattered storms are possible during the day with mainly an
   associated hail hazard.  The stronger updrafts may acquire supercell
   characteristics with some conditional tornado risk over southern AL.
    However, the primary severe threat will likely develop as the low-
   to mid-level wind field strengthens during the evening into the
   overnight.  Storms developing within the WAA regime and/or a
   thunderstorm cluster growing upscale into an MCS are seemingly the
   favored scenarios for storm development.  Severe gusts (some
   significant; 65+ kt) and tornadoes will likely become the main
   hazards as storms move east across northern LA eastward into MS and
   into western AL by early Saturday morning.  

   ...Southern Appalachian states...
   The northeastern periphery of richer low-level moisture (60s F
   dewpoints) will probably include GA and perhaps extend northward
   into the western Carolinas during the day.  Isolated to widely
   scattered multicells are forecast to develop during peak heating
   with an isolated hail/wind risk with the stronger storms.  This
   activity will likely diminish by early evening.

   ..Smith.. 04/08/2021

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