Fog is a fairly common New England weather feature, however, the Cataclysm could add both this and it’s own variant to the equation; streaming wisps of toxic vapors obscuring vision and being yet another good reason to remember some sort of face coverage.
Perhaps a random wind direction is chosen for each storm and streams/clouds of choking gas of some sort are blown across the screen, allowing even an unprotected player to try and dart to cover behind buildings or or obstructions.
I don’t think making the vapor particularly corrosive would be appropriate since we already have acid rain for that hazard, but ‘some’ sort of interesting effect beyond mere pain our coughing would be appropriate I think.