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ACUS11 KWNS 201801
SWOMCD
SPC MCD 201801
IAZ000-202030-

Mesoscale Discussion 0802
NWS Storm Prediction Center Norman OK
0101 PM CDT Wed Jun 20 2018

Areas affected...Central and east-central IA

Concerning...Severe potential...Watch possible

Valid 201801Z - 202030Z

Probability of Watch Issuance...40 percent

SUMMARY...An increase in thunderstorm development is expected this
afternoon across central and east-central Iowa, with some storms
becoming capable of producing a tornado, strong wind gusts, and/or
hail. Overall coverage of the severe-weather threat remains
uncertain at this time, though trends will be monitored for
potential watch issuance.

DISCUSSION...Trends in mosaic radar imagery indicated an increase in thunderstorm coverage into the early afternoon in the vicinity of a
pre-frontal boundary extending from north-central MO into southern
IA (to the southeast and east of KDSM). Despite filtered sunshine
tempering diabatic heating and the presence of modest midlevel lapse
rates, surface temperatures rising through the lower 80s in a rather
moist environment are resulting in moderate buoyancy for sustained
updrafts through the afternoon. Although effective bulk shear is
weak at this time, models suggest some increase is expected through
the afternoon that would support greater potential for storm
organization.

Early afternoon surface analysis showed an area of deepening low
pressure located just west of KDSM with a warm front extending east
into northern IL and northern IN, while a cold front trailed
south/southwest through northwest MO to southeast KS. Storms that
interact with the warm front will have an increased potential for
storm rotation, given the presence of ambient surface vorticity and
enhanced effective SRH. The latter factor is expected to increase
to 100-150 m2/s2 per RAP forecast later this afternoon across the
discussion area.

..Peters/Dial.. 06/20/2018

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

ATTN...WFO...DVN...DMX...

LAT...LON 41869432 42329394 42439311 42389222 42219172 41999140
41489140 41169169 40999202 40999260 41049313 41249369
41319402 41869432



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