Mesoscale Discussion 1207
NWS Storm Prediction Center Norman OK
0256 AM CDT Sat Jul 01 2017
Areas affected...Portions of west-central TX.
Concerning...Severe Thunderstorm Watch 387...
Valid 010756Z - 010900Z
The severe weather threat for Severe Thunderstorm Watch 387
SUMMARY...Severe winds and isolated large hail will remain possible
in the watch corridor for a few more hours before the activity
encounters less-favorable air and weakens. Although it is uncertain
how long this activity will remain organized at severe levels,
recent upscale growth, combined with a favorable inflow environment
just above the surface indicate the threat may persist across the
Big Country before activity weakens.
DISCUSSION...A long-lived small cluster of severe storms, that
formed yesterday afternoon in the southern Sangre de Cristos of
northern NM, has persisted into west Texas. Despite brief weakening
just east of the TX/NM line, this activity re-strengthened and
produced a 70-kt gust at the Levelland West Texas Mesonet site at
650Z. An additional severe-storm cluster developed to its east and
is crossing portions of Dickens/Crosby/Kent/Garza counties at this
time. The clusters may merge in the next 1-2 hours, leading to an
upscale-grown MCS that, in turn, would move east-southeastward to
southeastward north of an older outflow boundary that is analyzed
near a MAF-COM line, and along fresher, aggregated outflow
boundaries north of that.
The most probable corridor for a resulting severe threat corresponds
to the new watch, between the southern outflow boundary and what
appears to be prohibitively cool/stable outflow air across northwest
TX, where additional precip is reinforcing static stability.
Modified RAOBs and forecast soundings indicate this environment is
characterized by 1000-2000 J/kg MUCAPE and roughly 40-kt
northwesterly effective-shear vectors, which also may contribute to
a southeastward turn. A broad/35-40-kt LLJ is evident in VWP, with
associated isentropic lift over the outflows and to LFC expected to
support convective/severe potential for a few more hours, until the
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 31409930 31429951 31700083 32090169 32520219 32930220
32950220 33380208 33830155 33830152 33830140 33830125
33830087 33840051 32959909 32759909 32759909 32509909
32089912 31469919 31409930 31409930