I noticed that the Diamondback air horns seem to be an "all clear" signal for the whole park when rides are down due to bad weather.
When I went with my dad on Tuesday, DB shut down a little before 4 pm because a severe storm was rolling in. Hardly any rides were running for a few hours. About half of the park had cleared out and the storm was finally passing when Dad and I were on the Eiffel Tower. We were looking all around the park to see no coasters running, and hardly any rides running.
Then, out of the blue, we heard the Diamondback air horns and saw the first train going up the hill. Moments later, trains started going up on Beast, Vortex, and Racer, as if following DB's lead.