Alert archive / Iowa / Special Weather Statements in 2017

Special Weather Statement, NWS Des Moines, IA

August 21, 2017Mahaska County, Monroe County, Wapello County, Iowa

NWS Des Moines, IA issued this special weather statement at Aug 21, 2017, 7:29 PM CDT for Mahaska County, Monroe County, Wapello County, Iowa. It was in force for 61 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, 7:29 PM CDT (00:29 UTC)
Expired
Aug 21, 2017, 8:30 PM CDT
In force
61 min
Issued by
NWS Des Moines, IA

Counties Mahaska County, IA, Monroe County, IA, Wapello County, IA

The radar

The Des Moines radar (KDMX), 103 km from the middle of the area, began a volume at 00:30 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

Davenport, (KDVN), launched 00:00Z, 0.5 hours before the alert went out and 209 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-pSkew-T log-p diagram, Davenport, at 00:00Z on 2017-08-22Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 366 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Davenport, at 00:00Z on 2017-08-22The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 149 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
366 J/kg
Mixed-layer CIN
-168 J/kg
Mixed-layer LCL
1050 m above ground
0-6 km bulk shear
21 kt
0-1 km storm-relative helicity
149 m²/s²
0-3 km storm-relative helicity
124 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.2

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, 6:33 PM CDT, 56 minutes earlier.

Area forecast discussion, Aug 21, 6:33 PM CDT, 56 minutes before
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Hazardous weather outlook, Aug 21, 4:14 PM CDT, 3 hours 15 minutes before
Hazardous Weather Outlook
National Weather Service Des Moines IA
414 PM CDT Mon Aug 21 2017

IAZ004>007-015>017-023>026-033>036-044>046-222115-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Sac-Calhoun-Webster-Hamilton-
Crawford-Carroll-Greene-
414 PM CDT Mon Aug 21 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

There is a slight risk for severe storms through this evening.
All modes of severe weather is possible along with heavy rainfall
which could lead to localized flooding west.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Scattered non-severe thunderstorms are possible Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

IAZ027-028-037>039-047>050-057>062-070>075-081>086-092>097-222115-
Butler-Bremer-Hardin-Grundy-Black Hawk-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-
414 PM CDT Mon Aug 21 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Showers and thunderstorms are likely through tonight. A few storms
could be strong, with strong winds and small hail the main
threats. Localized urban and small stream flooding is
possible...especially west.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Scattered non-severe thunderstorms are possible Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely not be needed this evening, and
will not be needed the rest of the week.

Kotenberg

In the hours before

Special weather statement, Aug 21, 6:04 PM CDT, 1 hour 25 minutes before
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Special weather statement, Aug 21, 6:16 PM CDT, 1 hour 13 minutes before
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Special weather statement, Aug 21, 6:26 PM CDT, 1 hour 3 minutes before
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Special weather statement, Aug 21, 6:38 PM CDT, 51 minutes before
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Special weather statement, Aug 21, 6:52 PM CDT, 37 minutes before
Special Weather Statement
National Weather Service Des Moines IA
652 PM CDT MON AUG 21 2017

IAZ071>073-082>084-220100-
Clarke IA-Adair IA-Lucas IA-Union IA-Madison IA-Warren IA-
652 PM CDT MON AUG 21 2017

...Gusty Winds Moving Southward Into South Central Iowa...

At 652 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Indianola to near Greenfield. Movement was
southeast at 30 mph.

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

Locations impacted include...
Indianola, Creston, Winterset, Osceola, Chariton, Green Valley Lake,
Lakeside Casino, Avenue Of The Saints Event Center, Afton, Milo,
Murray, St. Charles, New Virginia, Truro, Martensdale, Orient,
Lacona, Lorimor, Lucas and Woodburn.

LAT...LON 4128 9448 4140 9355 4117 9333 4116 9333
      4116 9331 4102 9318 4090 9434
TIME...MOT...LOC 2352Z 335DEG 25KT 4136 9364 4126 9441

Ansorge
Special weather statement, Aug 21, 6:58 PM CDT, 31 minutes before
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The office that day

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

IssuedProductOfficeCountiesLasted
Aug 21, 8:13 PM CDTSpecial Weather StatementDMXAppanoose, Davis, Wapello, Wayne32 min

Nearby

Special Weather Statements in Iowa, 2017Every 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.