Story County's Emergency Management Department says the activation of emergency sirens during Wednesday's severe thunderstorms is good reminder about when they're used. Deputy Emergency Management Coordinator Melissa Spencer says the sirens are activated when a tornado warning is issued or when one is seen by a trained spotter. She says a couple of other conditions will prompt their use, as happened Wednesday with winds in excess of 70 miles per hour. Spencer says golf ball-sized hail will also promt the sirens. She says those sirens serve as a primary warning for those caught outside during a storm. Spencer says the emergency sirens are generally activated by local law enforemcent dispatchers. She says they can also be activated at the Emergency Management Department's request.