|Mesoscale Discussion 181|
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Mesoscale Discussion 0181
NWS Storm Prediction Center Norman OK
1115 AM CST Tue Feb 14 2017
Areas affected...Portions of western/southern LA and far east TX
Concerning...Tornado Watch 33...
Valid 141715Z - 141845Z
The severe weather threat for Tornado Watch 33 continues.
SUMMARY...The risk for damaging wind gusts and perhaps a couple of
tornadoes continues across Watch 33, though the severe potential
presently appears to be becoming increasingly isolated/conditional.
DISCUSSION...The latest mosaic radar imagery indicates a broken
squall line advancing eastward across portions of the lower Sabine
Valley vicinity, and this activity will continue to spread eastward
during the next few hours. Cloud tops accompanying the broader
convective system have been warming based on infrared satellite
imagery, implying an overall weakening convective trend.
Furthermore, surface pressure tendencies ahead of this activity are
small in magnitude. This is likely a reflection of the deeper ascent
accompanying a deamplifying midlevel cyclonic perturbation lagging
well to the northwest of richer Gulf moisture serving as inflow to
the convective system.
Nevertheless, the latest visible satellite imagery and surface
observations suggest that a more substantially modified Gulf air
mass continues advancing inland ahead of the aforementioned
activity. This air mass is preceded by a marine boundary extending
around 30-60 miles north of the southern LA coast. Diurnal surface
heating east of the ongoing convection -- especially where
mid/high-level cloud canopies are thinning -- may support sufficient
destabilization amidst this moisture for a conditional severe risk
persisting into the afternoon.
The LCH VAD wind profile indicates around 45-50 kt of 0-6-km bulk
shear with sufficient low-level directional shear for around 200
m2/s2 of 0-1-km SRH. As such, damaging winds and perhaps some
tornado potential could conditionally accompany deeper convective
elements embedded within the squall line -- especially if more
vigorous updrafts were to become separated within the line.
LAT...LON 29549223 29869397 30849412 31429386 31589350 31429295
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