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Why did sirens go off in the western suburbs of Des Moines on Sunday?

If you live in the western suburbs of Des Moines, you may have been surprised by thunder and sirens on Sunday evening.

There were thunderstorms and rain showers Sunday evening into early Monday morning. But no tornado warnings were issued for central Iowa. So why did the siren sound?

Why did the sirens go off on Sunday?

Technical problems caused sirens to go off in some western suburbs, including Grimes, Urbandale, Waukee and West Des Moines, around 9 p.m. Sunday, according to a Polk County Emergency Management official.

Westcom Emergency Communication, which oversees emergency siren notifications, did not respond to a request for comment when this article was published.

The National Weather Service issued a severe thunderstorm warning for parts of Adair, Dallas, Guthrie and Madison counties on Sunday at 8:42 p.m. The warning, which covered cities including Adel, Waukee and Winterset, included the threat of winds of 60 miles per hour. That’s below the standard for activating sirens in Dallas and Polk counties.

The warning was allowed to expire at 9:30 p.m. as storms continued, but fell below the severe storm thresholds.

More: What is the difference between a severe weather warning and a warning?

Des Moines Register journalists saw sirens sounding in several suburbs shortly before 9:10 p.m.

Why do storm sirens normally go off in central Iowa?

Just because there is thunder and lightning doesn’t necessarily mean the sirens will sound.

For Dallas and Polk counties, sirens will be activated in areas where the National Weather Service has issued a tornado warning. They are also activated for a severe thunderstorm warning if winds are observed or if a wind speed of more than 70 miles per hour is forecast.

During a tornado watch you will not hear sirens, but you will hear a warning, which can happen when a tornado or funnel cloud is reported by trained spotters. As for severe thunderstorms, there must be a wind speed of 70 miles per hour or more before the siren goes off.

More: What you need to know about monthly testing in the Des Moines area

When activated, the sirens sound for 3-5 minutes and repeat every 10-15 minutes while an alert is active. They do not sound continuously and do not provide an “all clear” warning when an alert expires.

Kate Kealey is a general assignment reporter for the Register. Reach her at [email protected] or follow her on Twitter at @Kkealey17.