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ACUS11 KWNS 161833
SPC MCD 161833

Mesoscale Discussion 1507
NWS Storm Prediction Center Norman OK
0133 PM CDT Wed Aug 16 2017

Areas affected...Portions of southern/eastern Kansas and far
northern Oklahoma

Concerning...Severe potential...Watch likely

Valid 161833Z - 162030Z

Probability of Watch Issuance...95 percent

SUMMARY...Scattered thunderstorms are forecast to develop by 2-3 PM
CDT, and a few of these storms will likely become severe with large
hail, damaging winds, and perhaps a couple tornadoes. Some of the
large hail could be over two inches in diameter. A watch will likely
be needed within the next couple of hours.

DISCUSSION...Satellite imagery and surface analysis early this
afternoon depict a somewhat complex pattern across parts of Kansas
and far northern Oklahoma. On the synoptic scale, a cold front
extends from western Oklahoma northeastward to a low over the mid
Missouri Valley. Furthermore, a remnant outflow boundary from
morning convection extends from the front over south-central Kansas
east to the Ozarks. Near/south of this boundary, rich low-level
moisture (e.g., 15.2 g/kg mean mixing ratio on the 18Z Springfield,
MO sounding) is combining with diurnal heating to promote MLCAPE
values upwards of 2000-3000 J/kg. While weak inhibition remains,
continued surface heating and mid-level cooling/moistening (on the
fringe of a broad vorticity maximum) should be sufficient for
convective initiation by mid afternoon.

East/northeastward advection of steeper mid-level lapse rates
towards the region, combined with effective shear around 35-40 kt,
will be favorable for a few initially semi-discrete cells capable of
large hail (some potentially greater than two inches in diameter).
Additionally, backed low-level flow near the outflow boundary may
yield enough storm-relative helicity for low-level rotation and a
couple tornadoes in any semi-discrete cells late this afternoon.
However, due to generally front-parallel deep-layer mean flow,
convective mode should quickly evolve to clusters and line segments,
transitioning the primary threat to damaging winds this evening as
cells gradually spread east.

With storms developing by 20 UTC (3 PM CDT), watch issuance will
likely be needed within the next 1-2 hours.

..Picca/Weiss.. 08/16/2017

...Please see for graphic product...


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