Unfortunately, there are relatively few places at the City that could be considered safe in the event of a tornado. The basement of the OMP might be one, the restrooms under the Riverfront Playhouse, the restrooms in the back of the Red Gold Heritage Hall, the restrooms under Christmas Hollow, the M&C warehouse, the foods warehouse under the employee lounge, the lower dressing rooms in Echo Hollow, the Mine Restaurant possibly, maybe the back areas of the Springhouse Restaurant. Behind the waterfall would not be safe. Some of the above mentioned places are not easily accessible to guests, neither will they accommodate large numbers of people, but it's the best we've got at the time.
The policy as to dealing with guests during bad weather has changed from time to time through the years. Currently, the policy is to inform guests, and then let them make their own decisions as to what to do. Employees are not supposed to tell guests to "go there" or "do that." This may leave some guests feeling confused or uncomfortable, but it's a policy that had to be developed because of the "litigation happy" society in which we now live. Consider...if a family was told by an employee to "go there," did so, and something really bad were to happen "there," the company and the employee could be considered liable. It's sad, but there are people who sue when their kid, running down Hill Street, falls and scrapes their knee.
The city's safety officers do keep a close eye on the weather on those days when the forecast calls for it to be threatening. They categorize several types of threatening weather, depending on the expected degree of severity and how close the bad weather is, into what they call "phase watches." I think there are four phases. Shops and venues are notified as to which phase we are under at the time, and they all have established procedures to follow accordingly. Shutting down an outdoor show when there is lightening in the area is an implementation of one of the phase procedures. They do have a park-wide address system which could be used to announce imminent danger to guests en masse, but I've never heard it used for that. Normally, information about weather is communicated to guests by word-of-mouth via shopkeepers and venue personnel, and then guests are left free to make their own decisions on what to do.