SPC AC 191937
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0137 PM CST Wed Jan 19 2022
Valid 192000Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TX TO
A couple tornadoes along with scattered damaging winds and hail will
be possible into this evening, mainly from east Texas across western
and northern Louisiana.
The ongoing outlook remains on track and no changes are needed with
the 20z update. Convection continues to increase ahead of the
surface cold front across parts of eastern TX into LA and far
southern AR where Severe Thunderstorm Watch 16 is now in effect. A
risk for hail, damaging gusts and a tornado or two will accompany
this activity into this evening. For more information on short term
severe potential reference MCD 0086.
.PREV DISCUSSION... /ISSUED 1018 AM CST Wed Jan 19 2022/
...East TX to the Lower MS Valley...
Boundary-layer heating of an increasingly moist wedge of partially
modified return-flow air (surface dew points from upper 50s to mid
60s F) and will help to offset modest mid/upper-level lapse rates to
yield MLCAPE peaking towards 1000-1500 J/kg across east TX at 21Z.
Ascent will occur both with the southeast-moving cold front in the
Ark-La-Tex to Ark-La-Miss and a pre-frontal, warm-sector convergence
zone in a warm-advection plume centered on southeast TX and the
Sabine Valley. This latter corridor is expected to contain primarily
discrete afternoon convection amid broad 50-60 kt 500-mb westerlies.
Guidance does suggest that hodograph weakness will be prominent
around 700 mb, until winds near this level strengthen in the
evening. As such, the productivity of supercells within a tornado
and hail context may be subdued given this initial weakness and the
modest upper-level lapse rates. Nevertheless, adequate low-level SRH
will exist for some tornado threat and 40-50 kt effective shear
magnitudes will support hail as well.
Convection along the advancing cold front will more quickly grow
upscale with a predominant cluster to linear mode during the early
evening. Main threat in this regime should be damaging winds and a
brief tornado or two from embedded LEWPs/mesovortices. Greater
low-level SRH may compensate for decreasing surface-based buoyancy
with eastern extent across MS until convection becomes elevated.
With time, convection should become increasingly parallel to
deep-shear vectors as upper support from the low-amplitude impulse
over OK shifts east of the region. While convection will likely
persist into the overnight across the northwest Gulf Coast to Lower
MS Valley, the severe threat should wane.
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