Severe Thunderstorm Warning 254, NWS Des Moines, IA

970 
WWUS53 KDMX 210244
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
944 PM CDT THU JUL 20 2017

IAC015-153-169-210315-
/O.CON.KDMX.SV.W.0254.000000T0000Z-170721T0315Z/
Polk IA-Story IA-Boone IA-
944 PM CDT THU JUL 20 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1015 PM CDT
FOR NORTHERN POLK...SOUTHWESTERN STORY AND SOUTHEASTERN BOONE
COUNTIES...

At 943 PM CDT, severe thunderstorms were located along a line
extending from Iowa State Center to Saylorville, moving east at 40
mph.

HAZARD...60 mph wind gusts. 

SOURCE...Radar indicated. In addition...several reports of tree 
         branches downed have been reported with these storms.

IMPACT...Expect damage to roofs, siding, and trees. 

Locations impacted include...
Ames, Ankeny, Urbandale, Johnston, Altoona, Grimes, Nevada,
Bondurant, Polk City, Huxley, Saylorville, Madrid, Mitchellville,
Slater, Granger, Saylorville Lake, Big Creek Lake, Adventureland
Amusement Park, Iowa State Center and Prairie Meadows.

This includes the following highways...
 Interstate 35 between mile markers 88 and 113.
 Interstate 80 between mile markers 141 and 149.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Prepare immediately damaging winds. People outside should move to a 
shelter, inside a strong building and away from windows.

Torrential rainfall is occurring with these storms, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4165 9381 4186 9382 4186 9384 4196 9385
      4208 9336 4166 9335
TIME...MOT...LOC 0243Z 262DEG 34KT 4200 9364 4168 9360 

HAIL...<.75IN
WIND...60MPH
 
$$

MF

234 
WWUS53 KDMX 210256
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
956 PM CDT THU JUL 20 2017

IAC015-210305-
/O.CAN.KDMX.SV.W.0254.000000T0000Z-170721T0315Z/
Boone IA-
956 PM CDT THU JUL 20 2017

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN BOONE COUNTY IS
CANCELLED...

The storms which prompted the warning have moved out of the warned 
area. Therefore, the warning has been cancelled.

LAT...LON 4165 9373 4187 9370 4199 9370 4208 9336
      4166 9335
TIME...MOT...LOC 0255Z 259DEG 35KT 4203 9352 4187 9348 4169 9348 

$$

IAC153-169-210315-
/O.CON.KDMX.SV.W.0254.000000T0000Z-170721T0315Z/
Polk IA-Story IA-
956 PM CDT THU JUL 20 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1015 PM CDT
FOR NORTHERN POLK AND SOUTHWESTERN STORY COUNTIES...

At 955 PM CDT, severe thunderstorms were located along a line
extending from near Nevada to 6 miles east of Huxley to Bondurant,
moving east at 40 mph.

HAZARD...60 mph wind gusts. 

SOURCE...Radar indicated. 

IMPACT...Expect damage to roofs, siding, and trees. 

Locations impacted include...
Ames, Ankeny, Urbandale, Johnston, Altoona, Nevada, Bondurant, Polk
City, Huxley, Saylorville, Mitchellville, Slater, Adventureland
Amusement Park, Prairie Meadows, Saylorville Lake, Maxwell,
Cambridge, Elkhart, Alleman and Sheldahl.

This includes the following highways...
 Interstate 35 between mile markers 88 and 113.
 Interstate 80 between mile markers 141 and 149.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Prepare immediately for damaging winds. People outside should move 
to a shelter, inside a strong building and away from windows.

Torrential rainfall is occurring with these storms, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4165 9373 4187 9370 4199 9370 4208 9336
      4166 9335
TIME...MOT...LOC 0255Z 259DEG 35KT 4203 9352 4187 9348 4169 9348 

HAIL...<.75IN
WIND...60MPH
 
$$

MF

246 
WWUS53 KDMX 210308
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
1008 PM CDT THU JUL 20 2017

IAC153-169-210315-
/O.CON.KDMX.SV.W.0254.000000T0000Z-170721T0315Z/
Polk IA-Story IA-
1008 PM CDT THU JUL 20 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1015 PM CDT
FOR NORTHEASTERN POLK AND SOUTHWESTERN STORY COUNTIES...

At 1007 PM CDT, severe thunderstorms were located along a line
extending from near Nevada to 9 miles west of Baxter to near
Mitchellville, moving east at 40 mph.

HAZARD...60 mph wind gusts. 

SOURCE...Radar indicated. 

IMPACT...Expect damage to roofs, siding, and trees. 

Locations impacted include...
Ames, Ankeny, Altoona, Nevada, Bondurant, Huxley, Mitchellville,
Adventureland Amusement Park, Prairie Meadows, Maxwell, Cambridge,
Elkhart, Weh-Weh-Neh-Kee State Park and Ankeny Regional Airport.

This includes the following highways...
 Interstate 35 between mile markers 88 and 96, and between mile
markers 106 and 113.
 Interstate 80 between mile markers 141 and 149.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

Torrential rainfall is occurring with these storms, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4165 9358 4189 9356 4202 9360 4208 9336
      4166 9335
TIME...MOT...LOC 0307Z 271DEG 35KT 4203 9336 4187 9332 4169 9332 

HAIL...<.75IN
WIND...60MPH
 
$$

MF

Area Forecast Discussion
National Weather Service Des Moines IA
613 PM CDT Thu Jul 20 2017

...Updated for 00z Aviation Discussion...

.SHORT TERM.../Tonight through Friday/
Issued at 302 PM CDT Thu Jul 20 2017

A weak surface frontal boundary has sagged southward into central
Iowa today and currently stretches roughly along the Highway 30
corridor. There is only a moderate temperature difference across
the boundary to the tune of about five degrees and dewpoints are
essentially the same on either side. Meanwhile a weak mid-level
shortwave is approaching along the South Dakota/Nebraska border,
generating a few light showers from around Sioux Falls down to
Lincoln. Heat indices are in the 100-110 degree range along and
south of the central Iowa frontal boundary in accordance with the
ongoing heat headlines.

There is some question as to whether or not we will see
thunderstorm development this evening associated with peak diurnal
heating. While instability values are very high weak capping
remains in place and there is no real upper-level forcing or
support for convection. Surface winds are weak with very little
convergence along the frontal boundary. Nevertheless, if the cap
can be breached we may see widely scattered thunderstorms near or
just south of the boundary, as we saw yesterday evening, and
slight chance POPs have been introduced accordingly. The magnitude
of instability supports a marginal severe weather threat, but
this is limited by the lack of organized forcing or shear. This is
well outlined by SPC products.

As the shortwave approaching from our northwest moves across
northern Iowa overnight, it will gradually draw the surface
boundary northward as a warm front and also support development of
more widespread thunderstorms over northern Iowa overnight.
Likely POPs have been maintained after midnight and again there
will be a severe weather risk. Given the high humidity/PWATs and
relatively slow forward motion of any storms there is a risk of
locally heavy rainfall, however the topography and antecedent
conditions in this area mitigate any flash flooding threat.

On Friday the boundary and associated convection will continue to
push north/northeastward through the day, possibly clearing our
area into Minnesota, and it will be very hot and humid once again.
given the orientation of the retreating boundary/storms and
associated heating, forecast heat index values exceed 105 degrees
a little north of the current advisory and west of I-35, so will
add a few counties up there in conjunction with expansion across
the Sioux Falls office forecast area in northwest Iowa.

.LONG TERM.../Friday night through Thursday/
Issued at 302 PM CDT Thu Jul 20 2017

Area of high pressure to the south still in control of much of the
area to begin the period with the broad upper ridge aloft. Start to
see some dampening of it by late Friday into the weekend, however
thermal ridge to be building in further with +26C at H85 by Friday
night across central IA. An upper trough to move through southern
Canada Saturday with an associated cold front dropping through the
state late Saturday into Sunday. This will finally break the heat
that has been in place across the state this week. Prior to this
however, a complex of thunderstorms expected to drop through the
northern/eastern portions of the area Friday night. Storms are
expected to develop in the late afternoon/early evening hours across
central MN and ride down the edge of the cap/instability gradient
southeastward. This may clip the northeast/east with potential for
severe storms. Additional development may occur on outflow
boundaries across the northern areas late that night as well when
the LLJ increases with moisture advection right into
northern/eastern IA Friday evening. PWATs push to around 2 inches,
so an abundance of moisture around and high freezing levels will
lead to efficient rain production. Storms appear to be progressive
and even with some storms over that area in the past few days, FFG
still 2.5 to 3 inches for 6 hours and 1.5 to 2 inches for 1 hour.
Therefore even with the threat of heavy rainfall, soil conditions
and current flash flood guidance suggests the area should be able to
take some rain before having too many issues. Also storm
mode/movement appear to be fairly progressive so again will still
monitor for heavy rain potential, but widespread heavy rain appears
low at this time.

H85 temps drop into the teens by Sunday and remain there into early
next week with much cooler temperatures expected by Monday/Tuesday
with highs only in the mid 70s to mid 80s. Upper ridging builds back
in for the middle of next week, with warmer temperatures building in
again as well. Thermal progs don't suggest temperatures as warm as
currently are in place, but expect highs to climb back into the 80s
and low to mid 90s. Another cool front to drop through the state
late Tuesday into the middle of the week. This boundary will remain
quasi-stationary across the state through the end of next week, so
will bring the next chances for rainfall/storms across the area. The
boundary right now appears to push south of the state toward Friday,
which may trend toward dry conditions just beyond the current
forecast period.

&&

.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 613 PM CDT Thu Jul 20 2017

Main concern this evening is possible thunderstorm development.
Both far western and far eastern Iowa have a thunderstorm at 00z
TAF issuance and have noticed recent cumulus development just
east of KDSM. Have not included VCTS at this time due to low
confidence in any storm impacting a terminal. However, expect
thunderstorms to increase in coverage after midnight into Friday
morning over northern Iowa and have VCTS mentioned. Outside of
thunderstorms, there may even be a small window around sunrise of
patchy fog bringing MVFR visibilities to KMCW and KALO.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT Saturday for IAZ057>062-
070>075-081>086-092>097.

Heat Advisory until 8 PM CDT Saturday for IAZ023-024-033>037-
044>050.

&&

SHORT TERM...Lee
LONG TERM...Beerends
AVIATION...Ansorge

Hazardous Weather Outlook
National Weather Service Des Moines IA
312 PM CDT Thu Jul 20 2017

IAZ057>062-070>075-081>086-092>097-211100-
Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek-Cass-Adair-Madison-
Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello-
Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis-
312 PM CDT Thu Jul 20 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

An Excessive Heat Warning is in effect for the area through
Saturday. Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

Widely scattered thunderstorms are possible this evening into
tonight, mainly north of Highway 34. A severe storm or two may
occur.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

An Excessive Heat Warning remains in effect for the area through
Saturday. Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

A few thunderstorms are possible between Friday night and Saturday
night, then again around Wednesday night. A few severe storms may
be possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not likely at this time.

IAZ023-024-033>037-044>050-211100-
Pocahontas-Humboldt-Sac-Calhoun-Webster-Hamilton-Hardin-Crawford-
Carroll-Greene-Boone-Story-Marshall-Tama-
312 PM CDT Thu Jul 20 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

A Heat Advisory is in effect for the area through Saturday.
Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

Thunderstorms are possible late this evening, then likely after
midnight tonight. A few severe storms and locally heavy rainfall
may occur.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

A Heat Advisory is in effect for the area through Saturday.
Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

Additional thunderstorms are possible Friday and Friday night,
then again by late Wednesday. A few severe storms and locally
heavy rainfall are possible Friday and Friday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed at times tonight and Friday.

IAZ004>007-015>017-025>028-038-039-211100-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Wright-Franklin-Butler-Bremer-Grundy-Black Hawk-
312 PM CDT Thu Jul 20 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Thunderstorms are possible late this evening, then likely after
midnight tonight. A few severe storms and locally heavy rainfall
may occur.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Additional thunderstorms are possible Friday and Friday night,
then again by late Wednesday. A few severe storms and locally
heavy rainfall are possible Friday and Friday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed at times tonight and Friday.

Lee

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
803 PM CDT THU JUL 20 2017

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

0801 PM     TSTM WND GST     3 NE WILLEY             42.01N 94.77W
07/20/2017  E60 MPH          CARROLL            IA   TRAINED SPOTTER

            SOME SMALL BRANCHES DOWN AS WELL.

&&

ANSORGE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
806 PM CDT THU JUL 20 2017

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

0805 PM     TSTM WND GST     3 W GLIDDEN             42.05N 94.79W
07/20/2017  M56 MPH          CARROLL            IA   PUBLIC

            49 KNOT/56 MPH WIND GUST AT CARROLL AIRPORT.

&&

ANSORGE

Special Weather Statement
National Weather Service Des Moines IA
850 PM CDT THU JUL 20 2017

IAZ046-047-058-059-210245-
Boone IA-Guthrie IA-Greene IA-Dallas IA-
850 PM CDT THU JUL 20 2017

...Strong Thunderstorms with Gusty Winds This Evening...

At 849 PM CDT, Doppler radar was tracking a strong thunderstorm near
Lake Panorama, or 9 miles northeast of Guthrie Center, moving east at
35 mph.

Half inch hail and wind gusts up to 50 mph will be possible with this
storm.

Locations impacted include...
Urbandale, Clive, Waukee, Grimes, Perry, Madrid, Dallas Center,
Granger, Panora, Woodward, Lake Panorama, Minburn, Bagley, Rippey,
Yale, Jamaica, Dawson, Bouton, Luther and Berkley.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4198 9383 4161 9381 4171 9450 4189 9450
TIME...MOT...LOC 0149Z 271DEG 31KT 4180 9440

MF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
905 PM CDT THU JUL 20 2017

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

0901 PM     TSTM WND GST     2 S DAWSON              41.82N 94.22W
07/20/2017  M59 MPH          DALLAS             IA   TRAINED SPOTTER

&&

ANSORGE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
910 PM CDT THU JUL 20 2017

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

0837 PM     TSTM WND DMG     BAGLEY                  41.85N 94.43W
07/20/2017                   GUTHRIE            IA   FIRE DEPT/RESCUE

            2 TO 3 FOOT DIAMETER TREE DOWN IN BAGLEY.
            TIME ESTIMATED FROM RADAR.

&&

ANSORGE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
918 PM CDT THU JUL 20 2017

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

0913 PM     TSTM WND GST     2 WSW MINBURN           41.75N 94.06W
07/20/2017  E60 MPH          DALLAS             IA   FIRE DEPT/RESCUE

&&

ANSORGE