Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 211937
SWOMCD
SPC MCD 211936
OKZ000-TXZ000-212130-

Mesoscale Discussion 1722
NWS Storm Prediction Center Norman OK
0236 PM CDT Sat Oct 21 2017

Areas affected...Western and central OK and part of western North TX

Concerning...Severe potential...Watch likely

Valid 211936Z - 212130Z

Probability of Watch Issuance...95 percent

SUMMARY...A new severe-weather watch will be coordinated soon across
portions of the southern Plains.  Thunderstorms are expected to
develop by late afternoon across western Oklahoma and into parts of
western North Texas, with storms becoming severe producing large
hail and perhaps a tornado with the initial activity.  Damaging
winds will become a greater threat as storms form a line, advancing
east across central Oklahoma into the evening.

DISCUSSION...Despite the lack of lightning so far, trends in visible
satellite imagery indicated sustained and deepening convection along
the portion of the cold front advancing southward through western OK
with some cooling of cloud tops.  Farther south into western North
TX, visible imagery indicated likely surface-based cumulus clouds
forming from southeast of CDS into Wilbarger County.  Objective
analyses indicated an increase of low-level convergence across this
latter area and the cold front, as a dryline shifts east through
northwest TX.  The warm sector has become moderately unstable
(MLCAPE 2000-2500 J/kg) with weakening of surface-based inhibition
per objective analyses along and just east of the surface
boundaries.  Additional surface heating and an increase in
large-scale ascent, as an upper trough moves east into the southern
Plains, are expected to aid in further weakening of the cap and
strengthening storm development from late this afternoon through the
evening.

An increase in deep-layer shear will support supercells with the
initial activity across western OK and western North TX, while
upscale growth is expected into the evening, with damaging winds
becoming the primary threat as a squall line evolves into central
OK.

..Peters/Thompson.. 10/21/2017

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

ATTN...WFO...TSA...FWD...OUN...

LAT...LON   34299996 35599953 36949829 36949689 36919663 36229668
            35069706 34159745 33689809 33519899 33849990 34299996




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