Day 1 Severe Weather Outlook

Valid 101200Z – 111200Z

…THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
OKLAHOMA INTO THE ARKLATEX…

…SUMMARY…
Severe thunderstorms are expected across the southern Plains into
the lower Mississippi Valley. Damaging winds are the greatest severe
risk, though tornadoes are possible along with very large hail
across the southern Plains.

…Southern Plains/Lower Mississippi Valley…

Late-evening water-vapor imagery depicts a well-defined short-wave
trough over AZ/northern Mexico, shifting east in line with latest
model guidance. This feature is forecast to advance into the
southern Rockies by 18z as 90 kt 500mb speed max rotates into the
base of the trough south of the Big Bend region. In response to this
trough, LLJ is forecast to increase across northwest TX which will
enhance low-level warm advection across western OK. Low-level
moisture is advancing northwest across OK and should aid buoyancy
for elevated convection between 12-14z. Forecast soundings suggest
elevated supercells are possible early in the period and this is
supported by CAMs with a cluster of convection that will spread
northeast across northern OK/southern KS. As this activity spreads
east into upper 50s/lower 60s dew points, convection will have an
opportunity to become surface based, though discrete cells may not
be particularly common as a polar front sags into this region.

Farther south, strong boundary-layer heating is expected across west
TX where surface-3km lapse rates are forecast to approach 9 C/km. At
the same time, strong mid-level height falls will spread across the
southern Plains by peak heating, and thunderstorms should easily
develop along the eastern edge of this steeper lapse-rate plume.
Latest thinking is scattered supercells will evolve from
east-central OK – north-central TX – southwestern TX between 19-21z.
This activity will be strongly sheared and could produce very large
hail early in the convective cycle. With time, multi-scale forcing
will encourage an extensive squall line that should race east toward
the Arklatex region. Damaging winds will likely be common along this
squall line as it advances across eastern OK/east TX during the
evening hours. Linear MCS will continue east during the overnight
hours, advancing to near the MS River toward the end of the period.

While damaging winds should be the primary threat with the squall
line, very strong shear and moist profiles will likely result in
embedded supercells. A few tornadoes are expected along the QLCS but
the lack of confidence in discrete pre-frontal supercells will
preclude more than 10% tornado probs during the day1 period.

..Darrow/Nauslar.. 01/10/2020

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