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ACUS11 KWNS 171410
SWOMCD
SPC MCD 171409
IAZ000-MNZ000-NEZ000-SDZ000-171545-

Mesoscale Discussion 1499
NWS Storm Prediction Center Norman OK
0909 AM CDT Wed Jul 17 2019

Areas affected...southeast SD...far southern MN...northeastern NE
and much of IA

Concerning...Severe Thunderstorm Watch 514...

Valid 171409Z - 171545Z

The severe weather threat for Severe Thunderstorm Watch 514
continues.

SUMMARY...Strong to severe storms may continue east/southeast across
IA through late morning. Storms could re-intensify this afternoon,
with an accompanying damaging wind threat spreading across much of
IA and a downstream watch may be needed.

DISCUSSION...An intense bow echo overnight has continued to produce
sporadic strong gusts of around 35-50 kt from FSD into northwest IA
over the least 60-90 minutes. Some weakening has been noted in radar
and lightning trends on the north end of the bowing segment along
the IA/MN border. Further south near the IA/NE border some periodic
intensification has been noted with isolated cells trying to develop
along the southern flank/outflow boundary across far eastern NE.
These storms remain in a weakly unstable environment above a capping
inversion, noted in regional 12z RAOBs. As strong heating occurs
ahead of the bow (temperatures already in the low 80s across
south-central IA), strong destabilization will occur, with forecast
MLCAPE values ranging from around 3000 J/kg across central IA to
around 1500 J/kg toward the MS River near eastern IA/western IL.
Strong effective shear will remain oriented along this instability
gradient as a shortwave impulse crests the Upper Midwest/northern
Plains upper ridge. Furthermore, thermodynamic profiles indicate
favorable conditions for a continuation and re-invigoration of
convection heading into the afternoon with very steep lapse rates
above a weak EML.

While there may be a relative lull in convective intensity this
morning due to weak capping, as heating and further destabilization
erode the cap, additional development by midday/early afternoon
could pose a more widespread threat across central into eastern IA.
Damaging wind gusts and hail are the most likely threat, however,
forecast hodographs do indicate sufficient SRH with backed low level
winds through 1km to support some tornado threat. This threat could
manifest through either mesovortex spin-ups if the bowing line
segment convective mode persists, or through supercell mesocyclone
processes if any discrete cells can form. Trends are being monitored
closely and a new watch downstream WW 514 may be needed in the next
1-2 hours.

Additional storms are developing in southern SD, likely atop the
cold pool with increased ascent due to the eastward migrating
shortwave impulse. This convection could post an isolated severe
threat through the morning but longevity of this activity is more
uncertain.

..Leitman/Guyer.. 07/17/2019

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

ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX...

LAT...LON   43919587 43439250 42569129 41889080 41139123 40969190
            40799326 41049534 41719666 42689805 43219816 43549779
            43849722 43919587



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