SPC 0700Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1140 PM CST Fri Dec 11 2020

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY NEAR THE
UPPER TEXAS COAST...

...SUMMARY...
A couple of strong storms could impact upper Texas coastal areas
Sunday afternoon, accompanied by some risk for severe weather.

...Synopsis...
Models continue to indicate that a vigorous short wave trough
digging out of the Arctic latitudes will be accompanied by a more
substantive cold intrusion into the northern Great Plains and Upper
Midwest by late Sunday night.  However, a belt of westerlies
emanating from the mid-latitude Pacific appears likely to maintain
considerable influence across much of the U.S. through this period.

Within the southern stream, one significant short wave trough is
forecast to dig to the lee of the southern Rockies by 12Z Sunday,
before turning eastward across the Red River Valley and Mid South,
ahead of another significant upstream perturbation digging across
the Pacific Northwest into the Great Basin by 12Z Monday.  Models
indicate little, if any, phasing of the lead perturbation with the
northern stream impulse, but associated forcing for ascent may
support modest surface wave development along an initially stalling
frontal zone across the Gulf States/lower Mississippi Valley into
the southern Great Plains.

There remains meaningful spread evident within the various model
output concerning these developments, which continues to contribute
to somewhat uncertain convective potential.  In general, though, it
does appear that at least some further moistening will support more
appreciable boundary-layer destabilization across the northwestern
into parts of the northeastern Gulf of Mexico, as deep-layer wind
fields and shear strengthen across much of the Gulf Coast states.

Stronger mid-level cooling and mid/upper forcing for ascent
associated with the progressive short wave trough likely will remain
displaced well inland from the boundary-layer destabilization over
the Gulf of Mexico.  However, moistening on return flow above the
cooler and more stable air mass inland of the coast will contribute
to weak elevated destabilization.  The latest NAM forecast
soundings, in particular, appear more suggestive that thermodynamic
profiles could become conducive to convection capable of producing
lightning. Although probabilities may be relatively low, this could
occur in a couple of swaths, including within the exit region of the
mid-level jet streak, across the Red River Valley into the
Ark-La-Miss vicinity, and perhaps in association with warm advection
to the northeast of the surface low track, across the lower
Mississippi Valley toward the southern Appalachians.

...Southeast Texas coastal vicinity...
As the primary frontal wave begins to form inland of upper Texas
coastal areas Sunday afternoon, there may be a window of opportunity
for modest boundary-layer destabilization in the presence of
strengthening deep-layer wind fields and shear.  This could
contribute to an environment favorable for scattered discrete
storms, one or two of which may intensify into supercells, before
associated forcing shifts northeastward by Sunday evening.

..Kerr.. 12/12/2020

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