Flash Flood — Polk, Iowa

2010-08-11 · near Santiago, Polk, Iowa

Event narrative

Water rescue in progress regarding three vehicles with a total of 11 people near NE 8th Ave and NE 54th Ave. There was one fatality, 10 rescues and several injuries.

Wider weather episode

Once again the atmosphere over Iowa became very unstable during the peak heating of the day. CAPE rose to 3500-4500 J/kg by the mid to late afternoon with lifted indices of -8 to -10 C. The moisture pooled over the state with precipitable water values approaching 2 inches by evening. High temperatures reached the upper 80s to low 90s, with dewpoints topping out in the upper 70s to low 80s. The atmosphere was fairly weakly sheared with 30 kts of available shear. Downdraft CAPE was between 1000 and 1800 J/kg. Available CAPE in the -10 to -30 C layer of the atmosphere was 800-1100 J/kg, but hail was limited by the high freezing level, 16,000 to 16,500 feet. Quarter size hail fell in Calhoun County as an intense storm passed though. The same storm cluster produced a funnel cloud in Sac County earlier. Scattered winds occurred with the storms. A 61 MPH wind gust was recorded in Eagle Grove for example and windows were blown out in Humboldt County south of Thor. One of the thunderstorms produced a tornado in Emmet County. The tornado touched down briefly over Lake Iowa. Thunderstorms became more organized during the evening and produced very heavy rainfall. In addition to the rainfall, scattered reports of high winds and some hail up to an inch and one quarter in size were received. Most of the wind reports were around 60 MPH. By far the most significant weather was the heavy rainfall. Three to 5 inches of rain fell on saturated ground, resulting in a very widespread flash flood event. Nearly half of the CWA was involved from parts of north central Iowa south to the Missouri border. Numerous roads were covered with flowing water of 1 to 2 feet in depth. Lightning struck a car at mile post 105 on Interstate 35 in Story County. No injuries were reported. Lightning also struck a house in Ankeny, causing a fire. The flash flooding claimed one life in central Iowa. Three vehicles were swept into the waters of Mud Creek near Altoona in Polk County. There were 11 people involved. A rescue call was made to save the occupants of the cars. One 16 year old female perished in the flood waters, the other 10 were rescued, though 4 were injured and received treatment at a local hospital. The flash flooding transitioned into widespread flooding as the night progressed into the day of the 11th. Flash flooding resulted in evacuations of apartments and trailer courts on the east side of Des Moines. Interstate 35 was covered by water due to flash flooding at mile post 97. Several cars spun out in the flood waters. Very intense rainfall in the Ames area resulted in a record crest on Squaw Creek. The creek crested 1.5 to 2.5 feet above the record high stage. Major flooding took place and the water treatment plant was inundated. Major damage was done to several buildings on the Iowa State Campus. Damage to Iowa State alone was between $40,000,000 and $50,000,000. Flooding from the Skunk River closed U.S. Highway 30. Thirty people were rescued at a Wal-Mart store in Ames as well. Following the severe flooding, several Iowa counties were added to the Presidential Disaster Declaration number 1930. The original 32 were: Adams, Appanoose, Audubon, Buena Vista, Butler, Cherokee, Clay, Davis, Decatur, Franklin, Howard, Humboldt, Iowa, Lee, Lyon, Madison, Marion, Mills, Monroe, Montgomery, O'Brien, Osceola, Palo Alto, Ringgold, Shelby, Union, Van Buren, Wapello, Warren, Wayne, Webster and Wright. Eighteen were added to the original, incuding: Black Hawk, Boone, Buchanan, Clayton, Delaware, Dickinson, Dubuque, Emmet, Fayette, Guthrie, Jackson, Jasper, Jones, Lucas, Mahaska, Polk, Sioux and Story. In addition, Governor Chet Culver had issued disaster proclamations for 50 Iowa counties due to inclement weather since June 1, 2010: Appanoose, Black Hawk, Boone, Buchanan, Buena Vista, Butler, Cherokee, Clay, Clayton, Davis, Decatur, Delaware, Dickinson, Dubuque, Emmet, Fayette, Franklin, Hamilton, Hancock, Howard, Humboldt, Jackson, Jasper, Jefferson, Johnson, Jones, Kossuth, Lee, Lucas, Lyon, Mahaska, Marion, Monona, Monroe, O'Brien, Osceola, Palo Alto, Polk, Ringgold, Shelby, Sioux, Story, Taylor, Union, Van Buren, Wapello, Warren, Washington, Webster and Wright.

View location on OpenStreetMap → (41.6445, -93.4387)

Source: NOAA Storm Events Database, event_id 240050. Narrative written by the NWS forecast office that issued the report.