Valid 272000Z – 281200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR PARTS OF WEST TX AND ACROSS WI/UPPER MI…
…SUMMARY…
Isolated severe thunderstorms are possible across parts of west
Texas during the late afternoon and evening, and from east-central
Minnesota to Upper Michigan this afternoon.
No updates required.
..Jewell.. 08/27/2019
.PREV DISCUSSION… /ISSUED 1120 AM CDT Tue Aug 27 2019/
…WI/Upper MI this afternoon/evening…
An embedded shortwave trough will move from MN across WI/Upper MI
this afternoon/evening, around the southern periphery of a
developing closed low over MB/western ON. Surface heating and
residual boundary-layer dewpoints in the low-mid 50s, beneath 500 mb
temperatures near -20 C, will result in low-midlevel lapse rates of
7-8 C/km and MLCAPE near 500 J/kg. Scattered low-topped
thunderstorms are expected in the corridor immediately preceding the
shortwave trough this afternoon/evening, and a few of the storms
could produce strong outflow gusts and hail approaching one inch in
diameter.
…Elsewhere…
The richer low-level moisture has been shunted south of the stronger
midlevel flow by a surface cold front and multiple convective
outflows from overnight convection that have now spread southward to
the I-20 corridor from north TX to central MS. Boundary-layer
dewpoints of 76-80 F are present south of the outflow boundaries
from southeast TX eastward, but vertical shear is weak and there is
little focus for storm initiation aside from the outflows. Isolated
strong gusts could occur with downbursts, but the overall severe
threat is too limited to warrant introduction of any damaging wind
probabilities. Farther west, very steep lapse rates were observed
at MAF, though surface temperatures in excess of 105 F are needed to
eliminate convective inhibition. There will be some threat for
storms late this afternoon into early tonight along the surface
front/stalling outflow, with isolated strong downbursts possible in
the steep lapse rate environment.
$$