Mesoscale Discussion 1/21/18

1:18pm Update. The SPC has issued a Mesoscale Discussion for parts of NTX, concerning a likely Tornado Watch to be issued shortly!

Probability of Watch Issuance…80 percent

SPC Summary

Areas affected…northeast Texas…eastern Oklahoma through western

Concerning…Severe potential…Tornado Watch likely

Valid 211913Z – 212115Z

Probability of Watch Issuance…80 percent

SUMMARY…Thunderstorms are expected to develop by 21Z across
northeast Texas into eastern Oklahoma and subsequently increase in
coverage and intensity. Supercells and bowing line segments with
damaging wind and a few tornadoes should be the primary threats. A
tornado watch will probably be needed before 21Z.

DISCUSSION…This afternoon a dryline extends from northeast KS
through west-central OK to north-central and southwest TX. Pacific
front will merge with the dryline later this afternoon, and this
boundary will continue through the southern Plains this evening as a
surface low consolidates over eastern KS in association with a
progressive shortwave trough. Modifying continental-polar air with
low 60s F dewpoints has advected through the warm sector beneath
modest lapse rates where objective analysis shows a corridor of
500-800 J/KG MLCAPE from central and northeast TX into southeast OK.
WV imagery indicates mid-upper level moistening and clouds resulting
from a band of deeper forcing for ascent moving through eastern OK
and northeast TX, and scattered showers are already developing over
northeast TX in association with this process. RAP soundings
indicate a capping inversion still in place around 750 mb, but
ascent in the 850-500 mb layer layer will eventually erode the
inversion, contributing to thunderstorm development by 20-21Z.
Vertical wind shear will increase as the low-level jet strengthens
within exit region of the approaching mid-upper jet with large 0-1
km hodographs and effective-bulk shear exceeding 40 kt. This
environment should support organized storms including a few discrete
supercells and bowing line segments as storms intensify later this
afternoon and evening.

..Dial/Grams.. 01/21/2018

…Please see for graphic product…


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