Thunderstorms are common in Iowa and can be very dangerous. They can bring intense wind, flash flooding, large hail and deadly lightning strikes.
Thunderstorms can produce damaging straight-line winds that can exceed 100 mph and cause damage equal to a tornado.
A thunderstorm is classified as “severe” when it produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher, or produces a tornado. Hail this size can damage property such as plants, roofs and vehicles while strong winds are able to break off large branches and knock over trees.
Thunderstorms are most likely to occur in the spring and summer months and during the afternoon and evening hours, but they can occur year-round and at all hours. The National Weather Service issues severe thunderstorm and tornado watches and warnings for severe thunderstorms.
What to do before, during and after a thunderstorm
Know your area's risk for a thunderstorm. They can occur year-round and at any hour.
Sign up for your community’s alerting system. Learn more about the Alert Iowasystem and how WEA alerts work. The NWS issues alerts by county, and warnings are issued to the area within the path of the storm.
Check the weather forecast before leaving to be outdoors for extended periods.
Postpone outdoor activities if thunderstorms are imminent. This is your best way to avoid being caught in a dangerous situation. Identify sturdy buildings close to where you live, work, study, and play so you can take shelter if necessary.
Clean up or remove hazards around your home. Cut down or trim trees that may be in danger of falling on your home. Secure outdoor furniture.
When thunder roars, go indoors! A sturdy building is the safest place to be during a thunderstorm.
If indoors, avoid running water or using landline phones. Electricity can travel through plumbing and phone lines.
Protect your property. Unplug appliances and other electric devices. Use power strips with surge protectors if possible.
If you are outside
If you can hear thunder, you are close enough to the storm to be struck by lightning. Seek shelter immediately!
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.
If boating or swimming, get to land and find a sturdy, grounded shelter or vehicle immediately.
Pay attention to authorities and weather forecasts for information on whether it is safe to go outside and instructions regarding potential flash flooding.
Avoid flooded roadways. Turn Around Don’t Drown®. Just six inches of fast-moving water can knock you down, and one foot of moving water can sweep your vehicle away.
Watch for fallen power lines and trees. Report them immediately.
Iowa Disaster History - 2020 Midwest Derecho
2020 August Derecho
4
fatalities
126
measured wind gust (MPH)
1.2M
without power
$11B
in damage
Iowa Disaster History
2020 Midwest Derecho
A derecho swept across the states of South Dakota, Nebraska, Iowa, Wisconsin, Illinois, Indiana, Michigan, & Ohio on August 10, 2020, leaving behind widespread damage. Video: CBS2/Fox 28 News.
