SPC AC 060558

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1158 PM CST Tue Jan 05 2021

   Valid 061200Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE TEXAS COASTAL PLAIN...

   ...SUMMARY...
   A few severe storms are possible today into tonight along the
   western Gulf Coastline. Primary hazards are expected to be damaging
   wind gusts and a couple tornadoes.

   ...Synopsis...
   A mid-level trough is expected to become more negatively tilted as
   it amplifies and crosses the southern Plains region. Immediately
   ahead of the trough, a surface low is also expected to intensify
   across central Texas, with a 40+ kt 850 mb jet advecting a
   seasonably moist low-level airmass across eastern Texas. Elevated
   convection is expected to develop along the nose of the low-level
   jet shortly after 12Z and traverses the OK/AR/KS/MO border area. By
   early afternoon, as the trough takes on a more positive tilt, a
   55-75 kt westerly mid-level jet is expected to rapidly overspread
   the warm sector across eastern TX. Deep forcing for ascent will
   encourage new thunderstorm development along and south of a warm
   front across east-central TX, and ahead of a cold front poised to be
   sweeping across the TX Hill Country. The strong westerly mid-level
   flow bisecting the south-southwesterly low-level jet will promote
   ample veering with height for organized thunderstorm updrafts, with
   a few severe storms likely.

   Meanwhile, another trough aloft, with multiple embedded mid-level
   impulses, will approach the West Coast. The first impulse is
   expected to reach northern California and southwest Oregon by
   morning. Despite deep-layer ascent, buoyancy is expected to be on
   the more marginal end, but should support a few lightning flashes.
   Later in the afternoon, a second impulse will approach the Pacific
   northwest, supporting a couple lightning flashes as well.  

   ...TX Coastal Plain...
   A warm front will slowly drift northward across east-central Texas
   through the day, with modest destabilization expected across the
   warm sector. Surface temperatures are expected to peak into the mid
   60s to near 70F, with lower 60s F dewpoints advecting northward from
   the Gulf of Mexico. With up to 6-7 C/km mid-level lapse rates
   expected to overspread the warm sector by mid-afternoon, resulting
   in up to 800 J/kg MLCAPE by afternoon peak heating. As the mid-level
   trough and associated deep-layer ascent approaches, the development
   of relatively more intense convection is expected around the 18-20Z
   time frame. While strong forcing along the cold front suggests that
   a squall line may develop through the afternoon along the Texas
   Coastal Plain, ample veering with height in the lowest 3 km suggests
   that semi-discrete supercells are possible, with at least transient
   low-level rotation expected. Any supercell structure that can become
   sustained and anchor to the warm front may ingest 150-300 m2/s2
   effective SRH, with a couple tornadoes possible. Given the
   aforementioned strong flow fields aloft, adequate downward momentum
   transport within the squall may foster multiple instances of
   damaging winds. A Slight risk has been introduced to account for the
   wind/tornado threat.

   Towards the end of the period (roughly 07-12Z), modest buoyancy may
   advect inland along portions of the southeast LA/MS coastline, where
   deep-layer and low-level shear would support storm
   organization/rotation. Any storms that can manage to root in the
   boundary layer and become surface based may also pose a risk of a
   couple damaging gusts and perhaps a tornado.

   ..Squitieri/Darrow.. 01/06/2021

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