When it was opened in 1996 they said it would never close! But during the heavy snow fall of 5th and 10th February the Second Severn Crossing bridge closed on both days. This was as a result of large pieces of ice falling from the upper stays onto vehicles crossing the bridge. Indeed several cars had lumps of ice smashing through their windscreens!
As a precaution the M48 Severn Suspension Bridge was closed as well on the 5th February resulting in massive traffic disruptions.
“Never say never” is one saying that springs to mind. Indeed a week after the bridge opened it was closed to traffic as a result of a large fire at Avonmouth. Thick acrid smoke from the fire travelled up the Severn Estuary forcing the closure of the bridge.