Special Weather Statement, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
710 PM CDT Mon May 15 2017

.UPDATE...
Issued at 710 PM CDT Mon May 15 2017

Line of severe storms continues to progress through northeastern
Iowa currently. This will likely be the main severe activity
across the area associated with the severe thunderstorm watch in
place across northern Iowa. However the LLJ is expected to
increase by late evening with additionally development likely on
the warm front pushing north across Iowa and into MN. At this time
it appears looking at hi-res models that additional development
would likely occur in southern MN, with a small chance across far
northern Iowa. Therefore even though thunderstorms chances wane in
the next few hours, will stick with the watch for the possibility
of additional development.

Also adjusted pops across far western portions late tonight for
activity across north central KS/south central NE that could push
into far west central Iowa in the early morning hours.

&&

.SHORT TERM.../Tonight through Tuesday/
Issued at 338 PM CDT Mon May 15 2017

Confidence: Medium

Warm front now retreating north...though instability continues to
increase...still seeing a fair amount of CIN this afternoon and
better forcing shifting north to along and north of the boundary.
Convection which had been more robust has weakened considerably over
the past hour.  Models suggest that convection will develop along
and north of the boundary again tonight with the better chances over
the northern border counties into Minnesota. The GFS/Euro both are
tending to refire the convection over northeast areas this evening
between 00 and 04z as the low level jet increases into the boundary.
Bulk shear values are modest tonight with 20 to 35kts forecast
through 06z increasing to near 40kts by 12z west. The increase in
bulk shear may help storms fire west/northwest into Minnesota prior
to 12z. Our outlook remains slight/enhanced across the north...
though some changes may be possible with the next update late this
afternoon. As the weak surface low moves north tonight the focus for
convection should shift into southern Minnesota by morning.  Lows
tonight will be quite warm with south winds and more summer-like
dewpoints through the region.  Tomorrow...there will remain a small
window of opportunity for convection during the morning before the
focus shifts to western areas by late afternoon/evening.  Strong
south southwest winds will develop through the day with mixing
lowering dewpoints somewhat by afternoon.  Highs will once again
reach the mid to upper 80s across the area with dewpoints remaining
in the 60s...and heat indices from 85 to near 90 south.  Over the
north still uncomfortable with similar conditions expected.

.LONG TERM.../Tuesday night through Monday/
Issued at 338 PM CDT Mon May 15 2017

Tuesday night the upper trough finally begins to lift out of the
Plains which then pushes the surface features northeast.  It is
expected that by mid to late evening the surface low will be in
central Nebraska with a warm front nosing into west central or
northwest Iowa. Showers or storms should increase across these area
during that time then expand and spread into central Iowa
overnight.  Given the shear, forcing and theta-e advection progged
to push across the state, Tuesday night still looks like severe
storms are possible with hail/wind the primary threats.

Showers/storms will be ongoing Wednesday and while severe storms are
possible the severe potential is a little muddier.  The potential
limiting factors will be the amount of instability with the cloud
cover, the warm front being north of the state and how much
instability we can realize.  Shear will be strong enough so if we
break out in sun for a bit, we should quickly destabilize and storms
will quickly erupt and become severe.

Wednesday night/Thursday the low lifts off and we have a relative
lull in the forecast.  Temps will be cooler by this time as well.

The next similar system lifts out of the Plains for Friday/Saturday
and though any storm chances will be confined to the south where the
instability will be better.  The rest of the area will see showers
with this system.  Sunday/Monday will be dry before the next system
impacts the area Monday night.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1243 PM CDT Mon May 15 2017

Concerns this period include ongoing convection...potential
redevelopment tonight and to a lesser extent clouds and winds.
Current cluster of storms over central Iowa is moving east along
the warm front and beginning to show greater organization...expect
trend to continue through 23z prior to exiting the area to the
east. Potential for some svr storms...though may pass between TAF
sites. KALO and KMCW still have a chance for some storms as areal
coverage increases somewhat over the north...though confidence
remains limited. Have included VCTS for now. Convection should
bypass the far south sites KDSM/KOTM and with only small chances
left at KFOD for now. Convection may redevelop aft 06z
west/northeast of area...but will need to monitor.  /rev

&&

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

&&

UPDATE...Beerends
SHORT TERM...REV
LONG TERM...FAB
AVIATION...REV

Hazardous Weather Outlook
National Weather Service Des Moines IA
1004 PM CDT Mon May 15 2017

IAZ004>007-015>017-023>026-161100-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-
1004 PM CDT Mon May 15 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Additional thunderstorms are possible late tonight. A strong to
severe storm is possible. Large hail and damaging winds would be
the main severe threats.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

The threat for storms will return Tuesday night into Wednesday
night. A few severe storms will be possible on Tuesday night with
large hail and damaging winds mainly over the northwest half of
the outlook area. Additional thunderstorms are expected on
Wednesday into Wednesday evening, however the threat for severe
weather remains difficult to determine. Heavy rainfall will
remain possible during this time which may lead to river rises or
even some localized flash flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed late tonight and again Tuesday
night.

IAZ027-028-035>039-045>050-057>062-070>075-081>086-092>097-161100-
Butler-Bremer-Webster-Hamilton-Hardin-Grundy-Black Hawk-Carroll-
Greene-Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-
Jasper-Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-
Union-Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
1004 PM CDT Mon May 15 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

The threat for storms will return Tuesday night into Wednesday
night. Strong to severe storms are possible Tuesday night mainly
north of Highway 30 and west of Interstate 35. Additional
thunderstorms are expected on Wednesday into Wednesday evening,
however the threat for severe weather remains difficult to
determine. Heavy rainfall will remain possible during this time
which may lead to river rises or even some localized flash
flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed Tuesday night.

IAZ033-034-044-161100-
Sac-Calhoun-Crawford-
1004 PM CDT Mon May 15 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Additional thunderstorms are possible late tonight. A strong
storm, possibly severe cannot be ruled out. Large hail and strong
wind gusts are the main threats with the storms.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

The threat for storms will return Tuesday night into Wednesday
night. A few severe storms will be possible on Tuesday night with
large hail and damaging winds the main severe threats. Additional
thunderstorms are expected on Wednesday into Wednesday evening,
however the threat for severe weather remains difficult to
determine. Heavy rainfall will remain possible during this time
which may lead to river rises or even some localized flash
flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed through late tonight and again
Tuesday night.

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PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE DES MOINES IA
922 PM CDT MON MAY 15 2017

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

0620 PM     TSTM WND GST     1 S PLAINFIELD          42.83N 92.54W
05/15/2017  M59 MPH          BREMER             IA   MESONET

            PLAINFIELD IDOT RWIS ALONG HIGHWAY 218.

&&

BSS

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE DES MOINES IA
925 PM CDT MON MAY 15 2017

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

0644 PM     TSTM WND DMG     TRIPOLI                 42.81N 92.26W
05/15/2017                   BREMER             IA   BROADCAST MEDIA

            KWWL SHARED A PUBLIC IMAGE OF DOWNED TREE IN
            TRIPOLI DUE TO STRONG WINDS. TIME ESTIMATED
            VIA RADAR.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1027 PM CDT MON MAY 15 2017

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

0616 PM     HAIL             4 E ROWAN               42.75N 93.48W
05/15/2017  E1.25 INCH       FRANKLIN           IA   TRAINED SPOTTER

            DELAYED REPORT.

&&

MJB

Special Weather Statement
National Weather Service Des Moines IA
1028 PM CDT MON MAY 15 2017

IAZ004>006-015-160415-
Palo Alto IA-Kossuth IA-Winnebago IA-Emmet IA-
1028 PM CDT MON MAY 15 2017

...Rapidly intensifying storms may produce dime size hail...

At 1027 PM CDT, Doppler radar was tracking a strong thunderstorm
near Union Slough, or 14 miles north of Algona, moving northeast at
35 mph.

Dime size hail will be possible with this storm.

Locations impacted include...
Union Slough, Armstrong, Buffalo Center, Bancroft, Swea City, Burt,
Titonka, Ringsted, Fenton, Lakota, Rake, Lone Rock and Ledyard.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Des Moines.

&&

A severe thunderstorm watch remains in effect until 100 AM CDT for
north central and northwestern Iowa.

LAT...LON 4350 9369 4344 9368 4304 9438 4335 9465
      4350 9430
TIME...MOT...LOC 0327Z 230DEG 30KT 4328 9424

Kotenberg