Lack of warning, software error kept tornado sirens silent in Naperville

Outdoor warning sirens in Naperville failed to activate during a July tornado because of a mistake in software installed in April, city officials say.

Another reason is that the National Weather Service had not issued a tornado warning for Naperville when the tornado hit.

The National Weather Service reported that the EF-0 tornado touched down near 95th Street and Route 59 at 5:40 a.m. on July 23. It damaged the roof of a shopping center and trees in several neighborhoods, including an area near Gardner Road and Washington Street that lost electricity due to lines damaged by falling limbs.

But when the tornado hit, there were no sirens.

Now Dan Nelson, Naperville's emergency management agency coordinator, has explained why in a memorandum to the city manager and city council.

In the memo, Nelson said the software is supposed to set off the sirens automatically if the weather service has issued a tornado warning for Naperville.

The sirens are supposed to go off automatically if any part of Naperville falls within the geographic boundaries of a tornado warning set by the weather service. They can also be set off manually by Naperville public-safety dispatch center workers if a written weather bulletin mentions Naperville.

But the weather service did not issue a tornado warning for the Naperville area at that time. The tornado arrived at 5:40 a.m. and left by 5:46 a.m., according to the memo.

It did issue a warning later, at 5:47 a.m., as the tornado was leaving Naperville and heading toward Romeoville. The geographic boundaries did cover a small portion of south Naperville and should have triggered the sirens automatically. The written warning did not mention Naperville.

An investigation by the city and the siren company determined that a configuration error, made when the automatic turn-on software was installed in April, is to blame. The company has fixed the error and is examining its sirens nationwide to make sure sirens go off when they should, according to the memo.

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