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ACUS11 KWNS 182217
SWOMCD
SPC MCD 182216
NEZ000-SDZ000-190015-

Mesoscale Discussion 1078
NWS Storm Prediction Center Norman OK
0516 PM CDT Wed Jul 18 2018

Areas affected...Central and southern South Dakota...northeast
Nebraska

Concerning...Tornado Watch 280...

Valid 182216Z - 190015Z

The severe weather threat for Tornado Watch 280 continues.

SUMMARY...Severe threat continues across Tornado Watch 0280, with
gusty winds and large hail becoming the predominant threats with
time. A few storms are approaching the southeast fringes of the
watch and trends are being monitored for the possibility of
southeastward extensions.

DISCUSSION...Multiple storms have developed across Tornado Watch
0280 within the past few hours. Shorter lived multicell clusters and
transient supercells have been the primary storm mode thus far, with
the exception of a longer lived, outflow dominant supercell in
Shannon County, South Dakota. Low-level shear and mid-level lapse
rates are rather mediocre for more organized supercell development,
though additional transient supercell structures with brief
low-level mesocyclones are possible within the next few hours.

A few southeastward propagating discrete storm structures have been
observed from Gregory to Yankton Counties in South Dakota, on the
southeast edge of Tornado Watch 0280. These storms may move a few
counties outside of the watch bounds, but within the narrow confines
of a northwest-to-southeast instability axis. As such, a local WW
extension may be necessary if these storms maintain their intensity.

Otherwise, storms in the western portions of the watch have
exhibited outflow tendencies as they surge to the southeast. Cold
pools associated with these storms may congeal and promote the
upscale growth of an MCS later this afternoon into the evening
hours. Strong gusty winds and large hail will then become the
primary threats.

..Squitieri.. 07/18/2018

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

ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

LAT...LON 43590257 43740290 44010295 44400282 44650278 45600235
45550173 45350107 45220038 45089992 44739909 44459875
43939805 43579762 43299743 43069722 42919708 42659690
42439674 42259668 42109675 41819739 41789780 41929842
42139936 43590257



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