SPC 1200Z Day 1 Outlook

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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