SPC MD 1571


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Mesoscale Discussion 1571
NWS Storm Prediction Center Norman OK
0722 PM CDT Fri Oct 12 2018

Areas affected...Portions of west TX

Concerning...Severe potential...Watch possible 

Valid 130022Z - 130245Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms are expected to increase in coverage and
intensity this evening into tonight. Isolated large hail and
damaging winds may occur with the strongest storms. A tornado or two
will also be possible. Depending on convective trends this evening,
a watch may be issued.

DISCUSSION...As of 0015Z, the remnants of tropical cyclone Sergio
are located over northern Mexico per water vapor satellite imagery,
moving northeastward towards southern NM and far west TX.
Large-scale ascent associated with this feature will overspread much
of west TX this evening into the overnight. Initial isolated
thunderstorms have already formed over the Davis and Glass
Mountains, and additional convective development appears likely over
the next couple of hours. A baroclinic zone/front that has been
reinforced by cloud cover and differential diurnal heating is
oriented generally east-west from roughly Pecos to Midland to
Sweetwater vicinity. This surface boundary will likely be a focus
for thunderstorms as a south-southeasterly low-level jet strengthens

Some heating to the south of this front and sufficient low-level
moisture return has allowed for weak instability to develop, with
latest RAP mesoanalysis estimating MLCAPE generally ranging from
500-1500 J/kg. With continued low-level moisture advection forecast
tonight, enough instability should remain to support surface to
near-surface-based thunderstorms. 40-50 kt of mid-level
southwesterly flow and a veering wind profile through mid levels are
resulting in 40-55 kt of effective bulk shear.

Two supercell thunderstorms ongoing across Pecos and Brewster
counties will continue to pose an isolated large hail and damaging
wind threat in the short term. Uncertainty remains concerning the
timing of additional thunderstorms over west TX. The most plausible
scenario appears to be for at least scattered thunderstorms to form
over the higher terrain of far west TX around 02-04Z, and
subsequently spread eastward along the baroclinic zone/front
tonight. The predominant storm mode is also uncertain, with
supercells and small clusters both possible. Regardless, isolated
large hail and locally strong/damaging winds may occur with any
supercell. A tornado or two will also be possible in the vicinity of
the front where low-level flow will have a more east-northeasterly
component, modestly enhancing streamwise vorticity. Watch issuance
is possible later this evening, and will be dependent on subsequent
storm development and evolution.

..Gleason/Guyer.. 10/13/2018

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   30460438 30760453 31300442 31790399 31990306 32300189
            32280084 31710062 31120071 30800083 30400153 30180318
            30170388 30460438 

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