SPC AC 160543

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1243 AM CDT Tue Mar 16 2021

   Valid 161200Z - 171200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM KANSAS TO
   TEXAS...

   ...SUMMARY...
   Scattered thunderstorms, some severe, are expected Tuesday night
   across the Plains from Kansas to Texas. Isolated severe can also be
   expected from the lower Mississippi Valley to Georgia. Strong wind
   gusts, hail, and a tornado or two are the severe threats.

   ...Kansas to Texas...

   Early-morning satellite imagery depicts a well-defined upper low
   over southern CA, digging toward the lower CO River Valley. This
   feature will shift east into the southern Rockies by 17/00z as 90kt
   500mb speed max translates across southern NM. Intense 12hr
   mid-level height falls (180m) will overspread the TX Panhandle into
   western OK by the end of the period as the jet max ejects into
   central OK by sunrise.

   Rich boundary-layer moisture currently extends across the coastal
   Plain of TX/LA where 65-70 surface dew points are observed. This air
   mass will begin advancing north in response to the approaching
   trough and 60F+ dew points should return across north TX and over
   much of the body of OK during the evening hours. Latest thinking is
   a sharpening dry line/Pacific front should emerge over the eastern
   TX Panhandle and scattered convection is expected to develop as
   moisture rushes into this boundary ahead of the intense large-scale
   forcing. Forecast soundings suggest very cold 500mb temperatures
   (sub -20C) will overspread northwestern portions of this moisture
   surge and very steep lapse rates should contribute to considerable
   instability. Forecast soundings suggest MUCAPE could exceed 2000
   J/kg along the cool side of the warm front with at least 2000 J/kg
   SBCAPE across the warm sector. Thunderstorms should develop
   immediately ahead of the surface low along/north of the warm front.
   Strong shear will encourage elevated supercells that should track
   northeast across KS during the overnight hours. Just south of the
   warm front, latest high res model data may not be generating enough
   convection given the very strong forcing. While capping may limit
   initiation well ahead of the boundary, scattered storms are expected
   along the wind shift. Large-scale forcing suggests a line of storms
   will ultimately evolve then progress east across OK and portions of
   northern/central TX by sunrise. Have introduced 5 percent tornado
   probabilities to the stronger forced region of OK to account for
   possible embedded mesos along the squall line; otherwise, damaging
   winds and hail are expected. Hail is the primary risk north of the
   warm front over KS.

   Very late in the period LLJ may increase into the Arklatex region.
   There is some concern that more discrete supercells could emerge
   along this corridor ahead of the front. It's not entirely clear this
   will occur before 12z so probabilities will reflect aforementioned
   squall line that should advance to near the AR border by sunrise. If
   it becomes more clear that warm advection will initiate supercells
   earlier, tornado probabilities will need to be increased across this
   region.

   ...Gulf States...

   Isolated thunderstorms are currently noted from the lower MS Valley
   into northern AL/GA where a warm front will likely hold through much
   of the period. Aside from weak warm advection, broad, but strong
   west-southwesterly mid-level flow is forecast to persist across this
   region through the period. 00z model guidance suggests somewhat
   stronger 850mb flow will be noted through early evening across AL
   into the Carolinas. This could encourage a corridor of convection
   near the warm front to gradually sag southeast. Given the relatively
   weak low-level flow/forcing will not increase severe probabilities
   across this region. Even so, hail, wind, and perhaps a tornado can
   not be ruled out this convection.

   ..Darrow/Lyons.. 03/16/2021

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