Special Weather Statement, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
347 AM CDT Wed Jun 14 2017

.SHORT TERM.../Today through Tonight/
Issued at 346 AM CDT Wed Jun 14 2017

Complex of storms stretching across the CWA from north to south
should continue to slowly push east northeast through the early
morning hours as an impulse evident on water vapor imagery lifts
northeast through central KS/eastern NE. Expect a dry period around
late morning to early afternoon for much of the area, with
redevelopment along the sfc trough axis possible by mid/late
afternoon which should be situated across eastern MN into
central/eastern IA. However boundary and sfc low to fill some and
wash out as it moves east and the upper level parent trough lifts
into south central Canada. Therefore expect overall storm coverage
and chance of severe to be somewhat limited given the limited
convergence in the area of the boundary and generally better
dynamics off to the north/east of the area. Second issue with
redevelopment will be how fast clouds/activity clears this am and
how much recovery can be obtained by peak heating. Therefore a
better chance for storms to the east of the area as well, as it may
take some time before redevelopment with the possibility of the
boundary having pushed east of the area by the time storms develop.

As for temperatures today, have gone with temps a little bit lower
than previously expected with the storms/clouds around this AM.
Still should see temps top out in the mid to upper 80s. Even though
dewpoints remain in the upper 60s to around 70 the slightly cooler
temps in the 80s should keep heat index values in check around 90.

.LONG TERM.../Thursday through Tuesday/
Issued at 346 AM CDT Wed Jun 14 2017

There is little change in overall forecast thinking for the long
term period tonight. The weak surface trough moving across Iowa
tonight will briefly scour out clouds and storms, however, it is
more of a wind shift with a barely detectable temperature gradient
and behind it we will reside in weak and nebulous surface flow
beneath brisk zonal flow aloft. This means temperatures will
remain warm on Thursday, probably in the upper 80s and lower 90s,
and any subtle impulse traveling through the zonal flow will be
sufficient to kick off additional convection. There has been a
relatively consistent signal among the various prognostic models
for such an impulse moving across the forecast area around
Thursday night, with a concurrent round of storms. Instability and
deep-layer shear will be sufficient to justify a risk of severe
weather, however, the timing, much less area, of any such threat
remain very uncertain. The best that can be said is that, given
the predicted instability gradient, severe storms are somewhat
more likely across the southern half of the forecast area than the
northern half, but even this is pretty low confidence. This is
well- expressed in the SPC Marginal Risk outlook for
Thursday/Thursday night.

Successive shortwaves moving through the zonal flow aloft will
result in repeat episodes of the Thursday night scenario on both
Friday night and Saturday night. Oddly, the strength and thus
forecast confidence of each of the three systems increases heading
into the future. For the second wave, the first being Thursday
night, there is general consensus that initial convective
development will occur somewhere over eastern Nebraska around
Friday evening, with rapid upscale eastward growth into one or
more convective complexes. The GFS and NAM solutions have been
showing a "splitsville" scenario, with some rain moving across
northern Iowa associated with the stronger forcing near the mid-
level shortwave, while apparently stronger storms dive southeast
across southern Iowa into the much higher instability. While it is
difficult to pin our hopes on such details on day 3-4, this does
fit with climatological expectations and is a distinct
possibility.

The third and strongest system will move very quickly across the
region from Saturday afternoon into Saturday night. Early
indications are that instability may be somewhat limited during
this time frame due to two days of convective overturning and
limited return flow. However, the lift and shear with this last
wave are much stronger and certainly favor some severe weather
threat once again, potentially for the fourth or fifth
consecutive day/night this week. If the instability is sufficient
for organized updrafts, which is certainly not a guarantee, then
the most likely convective scenario would be a forward-propagating
squall line with attendant wind threat.

All in all the period from Thursday through Saturday appears warm,
but not as hot as earlier in the week, and with multiple periods
of thunderstorm and severe weather chances. After the last,
strongest wave late Saturday we will be scoured out with
northwesterly flow aloft and significantly cooler and quieter
weather from Sunday through Tuesday.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1214 AM CDT Wed Jun 14 2017

The primary concern remains convective trends through the period.
Scattered storms entered western IA this evening and produced
outflow which will flip some TAF sites to west with some gusts for
a period. After that wind confidence is low with chaotic flow.
Cannot rule out lower conditions, but have kept TAFs VFR until
conditions dictate otherwise. Similarly have only mentioned
thunder based on near term terms with more generic VCSH later this
morning and again east in the afternoon when additional storms
could develop.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SHORT TERM...Beerends
LONG TERM...Lee
AVIATION...Small

Hazardous Weather Outlook
National Weather Service Des Moines IA
416 AM CDT Wed Jun 14 2017

IAZ004-005-015-023-024-033>035-044>046-057-058-070-151100-
Emmet-Kossuth-Palo Alto-Pocahontas-Humboldt-Sac-Calhoun-Webster-
Crawford-Carroll-Greene-Audubon-Guthrie-Cass-
416 AM CDT Wed Jun 14 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Periodic thunderstorm chances will return to the forecast on
Thursday night, Friday night, and late Saturday. Severe weather
may be possible at times, with damaging winds and large hail the
primary threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated at least through the day
Thursday.

IAZ006-007-016-017-025>028-036>039-047>050-059>062-071>075-
081>086-092>097-151100-
Winnebago-Worth-Hancock-Cerro Gordo-Wright-Franklin-Butler-Bremer-
Hamilton-Hardin-Grundy-Black Hawk-Boone-Story-Marshall-Tama-
Dallas-Polk-Jasper-Poweshiek-Adair-Madison-Warren-Marion-Mahaska-
Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-
Wayne-Appanoose-Davis-
416 AM CDT Wed Jun 14 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Non-severe thunderstorms will clear out of the area from west to
east early this morning.

Additional thunderstorm development is expected this afternoon and
evening. Some storms could be severe, with large hail and strong
winds the primary threats. The best chances for storms and severe
weather will be east of Interstate 35.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Periodic thunderstorm chances will return to the forecast on
Thursday night into Friday, again Friday night, then late
Saturday. Severe weather may be possible at times, with damaging
winds and large hail the primary threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible late today, and again at times
later in the week.

Lee

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Special Weather Statement
National Weather Service Des Moines IA
311 AM CDT WED JUN 14 2017

IAZ059-071>073-082-083-140845-
Clarke IA-Adair IA-Union IA-Madison IA-Dallas IA-Warren IA-
311 AM CDT WED JUN 14 2017

...Gusty Winds Possible and Frequent Lightning...

At 310 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Adel to 9 miles southeast of Creston.
Movement was east at 40 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
West Des Moines, Waukee, Norwalk, Creston, Winterset, Earlham, De
Soto, Van Meter, Jordan Creek Town Center, Green Valley Lake, Avenue
Of The Saints Event Center, Afton, Murray, St. Charles, Dexter,
Truro, Lorimor, Cumming, Patterson and East Peru.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4092 9447 4158 9421 4159 9379 4151 9379
      4151 9371 4091 9387 4090 9447
TIME...MOT...LOC 0810Z 259DEG 34KT 4158 9399 4096 9424

Beerends

Special Weather Statement
National Weather Service Des Moines IA
415 AM CDT WED JUN 14 2017

IAZ061-062-074-075-084-085-141000-
Poweshiek IA-Marion IA-Jasper IA-Lucas IA-Mahaska IA-Monroe IA-
415 AM CDT WED JUN 14 2017

...Gusty Winds and Frequent Lightning Expected...

At 414 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Newton to near Melcher-Dallas to near
Chariton. Movement was east at 40 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Newton, Oskaloosa, Pella, Knoxville, Chariton, Monroe, Pleasantville,
New Sharon, Melcher-Dallas, Iowa Speedway, Knoxville Raceway, Lake
Red Rock, Sully, Russell, Lovilia, Beacon, Bussey, Lynnville, Harvey
and Lucas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4128 9268 4098 9288 4098 9349 4116 9338
      4116 9333 4124 9333 4130 9329 4167 9316
      4169 9256
TIME...MOT...LOC 0914Z 270DEG 34KT 4166 9309 4130 9320 4099 9340

Beerends

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
544 AM CDT WED JUN 14 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0418 AM     TSTM WND DMG     4 W KNOXVILLE           41.32N 93.18W
06/14/2017                   MARION             IA   LAW ENFORCEMENT

            POWER POLES DOWN NEAR HIGHWAY S45 AND
            MCKIMBER STREET WEST OF KNOXVILLE.

&&

MJB

Special Weather Statement
National Weather Service Des Moines IA
627 AM CDT WED JUN 14 2017

IAZ057-070-071-141200-
Audubon IA-Adair IA-Cass IA-
627 AM CDT WED JUN 14 2017

...Dime Size Hail and 50 MPH Winds Possible...

At 626 AM CDT, Doppler radar was tracking a strong thunderstorm near
Griswold, or 13 miles south of Atlantic, moving northeast at 40 mph.

Dime size hail and wind gusts up to 50 mph will be possible with this
storm.

Locations impacted include...
Atlantic, Griswold, Anita, Exira, Adair, Lewis, Massena, Cumberland,
Brayton, Marne, Wiota, Lake Anita State Park, Cold Springs State
Park, Griswold Park, Atlantic Municipal Airport and Anita Municipal
Airport.

LAT...LON 4150 9515 4151 9504 4157 9504 4166 9488
      4157 9470 4150 9470 4150 9457 4117 9471
      4116 9481 4116 9516
TIME...MOT...LOC 1126Z 224DEG 33KT 4121 9503

Beerends