Thunderstorms are a common occurrence each spring and summer across the Midwest, and Iowa is not immune.
Each year, Iowa sees hundreds of severe and non-severe thunderstorms. Thunderstorms can be extremely dangerous storms which may bring deadly tornadoes and lightning, damaging high winds, and hail and can lead to flash flooding.
The National Weather Service issues Severe Thunderstorm Warnings for thunderstorms that are producing or are capable of producing winds of at least 58 MPH or hail of at least 1 inch in diameter.
Often times, severe thunderstorms may be much stronger than the minimum criteria.
August 9, 2009 – Large Hail in Iowa
A long-lived very severe thunderstorm traveled roughly along and just south of Highway 20 from northeastern Crawford County to Black Hawk County between about 8 am and noon. The storm produced copious amounts of very large hail as well as strong straight-line winds that drove the hail with much force, increasing the resulting damage. The storm cycled in intensity several times along its path with the first peak producing particularly severe hail damage along a swath through eastern Sac County and into far western Calhoun County. The second peak produced a path of even greater damage through Webster County, just missing Fort Dodge to the south and resulting in total destruction of crops around Callender and Otho. The largest hail fell with the third peak in Hardin and Grundy counties where the worst damage occurred in and around Eldora.
Hail 3 inches in diameter or larger was driven by 70 to 100 mph winds severely damaging virtually every structure and vehicle in the city and devastating all crops, trees, and vegetation. Some cars and trucks had every window broken and their bodies riddled with large dents. Nearly every north and west facing window in the city was broken, all but a few buildings required significant roof repair or replacement, and the siding was stripped completely off of some houses. At Pine Lake State Park just east of Eldora several participants in an archery competition were caught outside in the storm and suffered from large welts and bruises. Elsewhere there were numerous other injuries including reports of lacerations and broken bones from the wind-driven hail. Countless birds and wild animals were also killed during the storm.
There were 22 reports of injuries in Hardin County, 11 were serious enough for people to be taken to hospital. In addition, a 150 square mile area of crops in Hardin County was also damaged. Total crop losses were reported on 45,000 acres, with 60% or greater loss on another 55,000 acres. Hail damage from Otho to Callender and surrounding areas in Webster County was described as the worst seen in 20 years. Estimates of crop damage were over $175,000,000. Iowa Governor Chet Culver declared Hardin and Webster Counties state disaster areas shortly after the storm.
June 29, 1998 – Derecho Sweeps across Eastern Iowa
An incredible complex of severe thunderstorms produced widespread extreme straight-line wind damage across much of Iowa, particularly areas from just northwest of Des Moines through the metro and east southeast to the Mississippi River before moving on through Illinois, Indiana, and Kentucky. This complex of storms originated in northern Nebraska during the early morning hours then moved east southeast into central Iowa where it interacted with changing atmospheric conditions and intensified further.
A tornado cut an 11 mile path across Crawford County damaging dozens of residences and numerous outbuildings. Several other more brief tornado touchdowns were reported as the storms cut a path across Iowa, along with occasional large hail ranging in size up to 2.5 inches in diameter at Des Moines, but the majority of the damage was produced by very severe straight-line winds. The line of storms produced winds of 70 to 90 mph along its entire length, with embedded swaths of even stronger winds in some areas. In the Des Moines metro area one such swath extended from around Granger through Johnston and northeastern Des Moines, with post-storm damage surveys indicating wind gusts of around 120 mph. Trucks and heavy construction equipment were blown over on the interstates and hundreds of homes and other buildings were unroofed or otherwise severely damaged in the metro with countless reports of trees falling on homes.
Further east the storms produced more extreme wind damage near and south of Iowa City, with an observer at Muscatine recording a wind gust of 104 mph and an unofficial instrument in Washington measuring an incredible 123 mph gust, which is the highest unofficial wind gust ever measured in Iowa. In Iowa City several cars of a freight train were blown off a railroad bridge over the Iowa River and plunged into the water below. At the height of the storm approximately 500,000 people in Iowa were without power and in some areas electricity was not restored for nearly a week. Thousands of homes and buildings were damaged across the state and at least 125 people were injured by flying debris but fortunately there were no fatalities.
Preparedness
Before the Storm:
- Know the county in which you live and the names of nearby major cities.
- Check the weather forecast before leaving to be outdoors for extended periods.
- Watch for signs of approaching storms.
- Have a NOAA Weather Radio with a warning alarm tone and battery back-up to receive warnings.
- Postpone outdoor activities if thunderstorms are imminent. This is your best way to avoid being caught in a dangerous situation.
- Check on those who have trouble taking shelter if severe weather threatens.
When Thunderstorms Approach:
- Move to a sturdy building or car. Do not take shelter in small sheds, under isolated trees, or in convertible automobiles.
- If lightning is occurring and a sturdy shelter is not available, get inside a hard top automobile and keep the windows up.
- Get tout of boats and away from water.
- Telephone lines and metal pipes can conduct electricity. Unplug appliances not necessary for obtaining weather information. Avoid using the telephone or any electrical appliances.
- Do not take a bath or shower.
If Caught Outdoors and No Shelter is Nearby:
- Find a low spot away from trees, fences, and poles. Make sure the place you pick is not subject to flooding.
- Stay away from metal conductors such as wires or fences. Metal does not attract lightning, but lightning can travel long distances through it.
- If you are boating or swimming, get to land and find shelter immediately!
Information Courtesy: National Weather Service Des Moines, Iowa