The Des Moines metropolitan area, located in Central Iowa, sits within a region recognized for its frequent and sometimes violent severe weather events. While tornadoes can occur in any month, Iowa’s seasonal weather patterns make it a particularly active area for powerful storm systems. Understanding the local risk for tornado activity is important for residents and visitors. This high-level risk requires a clear understanding of Des Moines’s specific threat profile and the local procedures in place to protect the population.
Des Moines’ Tornado Risk Profile and Frequency
Des Moines is situated in Polk County, which has a notable history of tornadic activity. Historical data for Polk County records an average of approximately 0.5 tornadoes per year, though the last decade has seen a higher frequency, averaging around 1.6 events annually. This places the county in a high-risk category compared to the national average. Polk County records show 81 confirmed tornadoes since the 17th century, including the deadliest event, an F4 tornado in 1896 that resulted in 21 fatalities. The peak month for these occurrences is May, accounting for over a third of all historical events.
Iowa’s Geographic Position and Tornado Seasonality
Iowa’s geographic location is a primary factor in its high susceptibility to severe weather, placing it within the zone known as “Tornado Alley.” The state is positioned where three distinct air masses frequently collide, creating the necessary atmospheric instability. Warm, moist air from the Gulf of Mexico meets colder, drier air masses descending from the Rocky Mountains and Canada. This intersection creates wind shear, where wind speed and direction change rapidly with height, initiating the horizontal rotation necessary for a supercell thunderstorm. The peak tornado season for Central Iowa, including Des Moines, generally runs from April through June.
Local Emergency Notification Procedures
Residents of Des Moines and the surrounding Polk County are alerted to imminent tornado threats through a layered communication system. The outdoor warning sirens are activated when a tornado has been sighted, indicated by radar, or when straight-line winds reach or exceed 70 miles per hour. These sirens are primarily designed to alert individuals who are outdoors to seek shelter and gather more information. For direct and personalized alerts, residents can register for the Polk County/Alert Iowa system, which delivers severe weather alerts directly to registered phones via voice call, text message, or email. The National Oceanic and Atmospheric Administration (NOAA) Weather Radio All-Hazards is another reliable tool, providing continuous, direct broadcasts from the National Weather Service.
Essential Tornado Safety and Shelter Planning
The most effective way to ensure personal safety is to establish a clear, pre-planned shelter strategy well before a storm is on the horizon. The safest place to be during a tornado is the interior part of a basement or a dedicated storm cellar, as these locations offer the best protection from high winds and flying debris. If a building does not have a basement, the safest alternative is a small, windowless, interior room on the lowest floor. This safe space should be a center hallway, a closet, or an interior bathroom, keeping as many walls as possible between the occupants and the outside. Once in the shelter, individuals should get under something sturdy, such as a heavy table, and use their arms to protect their head and neck. Never remain in a vehicle or a mobile home during a warning, as these structures offer minimal protection.
Preparing a basic emergency kit, often called a “Go-Kit,” is also prudent, containing essentials such as:
- A battery-powered radio
- A flashlight
- Water
- Necessary medications