SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0647 AM CST Sun Dec 13 2020

Valid 131300Z - 141200Z


Damaging winds and a couple tornadoes are possible across a portion
of southeast Texas and southwest Louisiana, mainly from
mid-afternoon to early evening.

...Southeast TX to LA and southwest MS...
Primary severe potential is expected to peak this afternoon into
early evening. Although confidence is not high, the conditional
threat for a couple tornadoes and damaging winds appear large enough
to warrant a Slight Risk delineation centered on the Lower Sabine

A vigorous shortwave trough over the southern High Plains will move
east into the TN Valley by early Monday. Resultant cyclogenesis
across the TX Gulf Coast by midday should result in gradual
deepening of the low as it tracks from near Houston to Atlanta by
12Z. A richly moist warm sector characterized by 68-71 F surface dew
points was present across the northwest Gulf and the Lower TX Coast,
supporting a plume of MLCAPE from 500-1500 J/kg, as sampled by the
12Z Corpus Christi and Brownsville soundings. This will probably
spread as far northeast as southwest LA.

Initially elevated convective development should further blossom
across east TX this morning. As forcing for ascent strengthens and
low-level warm theta-e advection persists, convective development
into the confined warm sector appears possible by mid-afternoon.
Enlarged low-level hodographs coinciding with the northeast extent
of surface-based instability should support a conditional risk for a
couple embedded supercells with the primary hazard being a tornado,
centered on the Lower Sabine Valley. Low-level winds are progged to
become increasingly veered with southwest extent during the
afternoon and a predominant cluster mode early in the convective
life cycle should mitigate a greater tornado threat.

During the late afternoon to early evening, a narrow squall line
should evolve across far southeast TX into northern LA and progress
east across most of LA into MS before weakening. Strengthening
700-mb flow behind this line should aid in potential for isolated
severe gusts across far southeast TX and southwest LA. Low-level
stability will be a limiting factor with northern/eastern extent,
but a threat for isolated damaging gusts should exist given the
increasingly impressive kinematic profiles.

..Grams/Goss.. 12/13/2020

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