Alert archive / Iowa / Special Weather Statements in 2017

Special Weather Statement, NWS Des Moines, IA

August 21, 20174 counties in Iowa

NWS Des Moines, IA issued this special weather statement at Aug 21, 2017, 9:43 AM CDT for 4 counties in Iowa. It was in force for 62 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 21, 2017, 9:43 AM CDT (14:43 UTC)
Expired: Aug 21, 2017, 10:45 AM CDT
In force: 62 min
Issued by: NWS Des Moines, IA

Counties Calhoun County, IA, Humboldt County, IA, Pocahontas County, IA, Webster County, IA

The radar

The Des Moines radar (KDMX), 106 km from the middle of the area, began a volume at 14:42 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Omaha, NE (KOAX), launched 12:00Z, 2.7 hours before the alert went out and 215 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 107 J/kg
Mixed-layer CIN: -350 J/kg
Mixed-layer LCL: 1132 m above ground
0-6 km bulk shear: 34 kt
0-1 km storm-relative helicity: 209 m²/s²
0-3 km storm-relative helicity: 421 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 11.7

Open this sounding in Storm Lab

The text

As transmitted.

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What forecasters said that day

The local office's own words before this special weather statement went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Des Moines, IA wrote its last area forecast discussion before this special weather statement went out at Aug 21, 7:05 AM CDT, 2 hours 38 minutes earlier.

Area forecast discussion, Aug 21, 7:05 AM CDT, 2 hours 38 minutes before

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Hazardous weather outlook, Aug 21, 4:03 AM CDT, 5 hours 40 minutes before

Hazardous Weather Outlook
National Weather Service Des Moines IA
403 AM CDT Mon Aug 21 2017

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-220915-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-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-
403 AM CDT Mon Aug 21 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Periods of thunderstorms will occur today and tonight. There is a
marginal risk for hail and strong wind with the storms this
morning, along with heavy rainfall that could lead to localized
flooding.

There is a slight risk for severe storms late this afternoon and
tonight. All modes of severe weather is possible along with heavy
rainfall which could lead to localized flooding. Very large hail
is possible across much of central Iowa especially north of
Interstate 80 and west of Interstate 35. Damaging wind and a few
tornadoes are possible across all of central Iowa.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

FAB

In the hours before

Local storm report, Aug 21, 8:23 AM CDT, 1 hour 20 minutes before

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Local storm report, Aug 21, 8:26 AM CDT, 1 hour 17 minutes before

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Local storm report, Aug 21, 8:27 AM CDT, 1 hour 16 minutes before

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Local storm report, Aug 21, 8:34 AM CDT, 1 hour 9 minutes before

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Special weather statement, Aug 21, 9:34 AM CDT, 9 minutes before

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Special weather statement, Aug 21, 9:43 AM CDT, 0 minutes before

Special Weather Statement
National Weather Service Des Moines IA
943 AM CDT MON AUG 21 2017

IAZ023-024-034-035-211545-
Humboldt IA-Calhoun IA-Webster IA-Pocahontas IA-
943 AM CDT MON AUG 21 2017

...Gusty Winds and Hail Possible over Northwest Iowa...

At 940 AM CDT, Doppler radar was tracking a strong thunderstorm near
Rockwell City, moving northeast at 20 mph with another strong storm
exiting Buena Vista County into Pocahontas County.

Nickel size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Fort Dodge, Pocahontas, Rockwell City, Dakota City, Humboldt, Lake
City, Manson, Laurens, Gowrie, North Twin Lake, Fort Dodge Regional
Airport, South Twin Lake, Dayton, Stratford, Pomeroy, Fonda,
Coalville, Rolfe, Badger and Otho.

LAT...LON 4290 9397 4247 9397 4247 9394 4222 9393
      4221 9485 4247 9486 4248 9488 4290 9492
TIME...MOT...LOC 1440Z 243DEG 15KT 4244 9453

Small

The office that day

Everything else NWS Des Moines, IA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 20, 11:03 PM CDT	Special Weather Statement	DMX	Crawford	27 min
Aug 20, 11:05 PM CDT	Severe Thunderstorm Warning	DMX	Carroll, Crawford, Sac	40 min
Aug 21, 12:32 AM CDT	Flash Flood Warning	DMX	Crawford	6 hr
Aug 21, 1:27 AM CDT	Special Weather Statement	DMX	Audubon, Guthrie	33 min
Aug 21, 1:31 AM CDT	Flash Flood Warning	DMX	Audubon, Carroll, Crawford, Guthrie	6 hr
Aug 21, 1:53 AM CDT	Special Weather Statement	DMX	Cass	22 min
Aug 21, 1:55 AM CDT	Severe Thunderstorm Warning	DMX	Emmet, Palo Alto	35 min
Aug 21, 2:07 AM CDT	Severe Thunderstorm Warning	DMX	Adair, Adams, Audubon, Cass, Guthrie	53 min
Aug 21, 2:46 AM CDT	Severe Thunderstorm Warning	DMX	Adair, Adams, Cass, Guthrie, Madison, Union	44 min
Aug 21, 3:02 AM CDT	Special Weather Statement	DMX	Kossuth	43 min
Aug 21, 3:30 AM CDT	Severe Thunderstorm Warning	DMX	Adair, Adams, Ringgold, Taylor, Union	32 min
Aug 21, 11:23 AM CDT	Special Weather Statement	DMX	Humboldt, Pocahontas	52 min
Aug 21, 1:39 PM CDT	Special Weather Statement	DMX	Emmet, Kossuth, Palo Alto	66 min
Aug 21, 2:02 PM CDT	Severe Thunderstorm Warning	DMX	Emmet, Kossuth, Palo Alto	29 min
Aug 21, 3:43 PM CDT	Special Weather Statement	DMX	Calhoun, Carroll, Crawford, Emmet, Humboldt, Kossuth and 4 more	77 min
Aug 21, 5:03 PM CDT	Special Weather Statement	DMX	Audubon, Boone, Cass, Dallas, Greene, Guthrie and 4 more	57 min
Aug 21, 5:37 PM CDT	Special Weather Statement	DMX	Boone, Grundy, Hamilton, Hardin, Story	53 min
Aug 21, 6:04 PM CDT	Special Weather Statement	DMX	Jasper, Polk	41 min
Aug 21, 6:16 PM CDT	Special Weather Statement	DMX	Madison, Warren	44 min
Aug 21, 6:26 PM CDT	Special Weather Statement	DMX	Black Hawk, Grundy, Marshall, Tama	64 min
Aug 21, 6:38 PM CDT	Special Weather Statement	DMX	Jasper, Mahaska, Marion	52 min
Aug 21, 6:52 PM CDT	Special Weather Statement	DMX	Clarke, Lucas, Madison, Union, Warren	68 min
Aug 21, 6:58 PM CDT	Special Weather Statement	DMX	Poweshiek	47 min

Nearby

Special Weather Statements in Iowa, 2017 Every special weather statement in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.