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ACUS11 KWNS 201932
SWOMCD
SPC MCD 201931
IAZ000-MOZ000-KSZ000-NEZ000-SDZ000-202130-

Mesoscale Discussion 1483
NWS Storm Prediction Center Norman OK
0231 PM CDT Thu Sep 20 2018

Areas affected...Portions of western Iowa...eastern Nebraska...
north-central and northeastern Kansas...and far northwestern
Missouri.

Concerning...Severe potential...Watch likely

Valid 201931Z - 202130Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms capable of severe wind gusts will slowly
increase along the front and move east throughout the
afternoon/early evening. A Severe Thunderstorm Watch may be needed
for at least portions of the area.

DISCUSSION...A cold front trailing into southeastern Colorado from a
deepening surface low near SUX will serve as the primary forcing
mechanism for thunderstorm development this afternoon over this
area. The strong frontal forcing, rather weak shear in the
cloud-bearing layer, and veered low-level winds will support a
rather quick evolution to a squall line mode, especially along the
sharper portion of the front in Nebraska and far northern Kansas, as
depicted in multiple convection-allowing model guidance through the
morning. The consolidating cold front/narrow cold pool is expected
to undercut the squall line, which will limit the overall severe
threat. However, a deeply-mixed boundary layer with mixed-layer
LCLs of 1600-2200 m and moderate mid-level lapse rates could support
damaging wind gusts with the stronger embedded downdrafts that can
remain close to the front.

Farther west, thunderstorms have developed along and slightly behind
the front in eastern Colorado and far western Kansas aided by the
southern fringe of an elongated mid-level vorticity maximum. These
storms may evolve more as cluster compared to the squall line to the
northeast, but rather weak low-to-mid-level shear magnitudes should
prevent any long-lived organization with these storms. However,
severe wind gusts are possible given the moderate lapse rates and
evaporation potential in the deeply-mixed boundary layer as they
push east into west-central Kansas through the mid-late afternoon.

Overall, a Severe Thunderstorm Watch may be needed for at least
portions of the MCD area to cover the severe wind threat.

..Coniglio/Hart.. 09/20/2018

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

ATTN...WFO...DMX...EAX...FSD...OAX...TOP...ICT...GID...

LAT...LON 42339709 42659676 42979613 42949493 42869434 42589379
41889388 40449476 39749536 39199627 38509775 38479883
39559904 40329881 40609866 41089836 42339709



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