The most common cause of misfires is a bad coil pack or packs. Damp, rainy, humid weather intensifies the misfires as the condensation makes the shorting out worse.

When the engine misfires, raw fuel gets dumped into the catalytic converter, if enough raw gas get into the converter it can permanetly destroy it.

A possibility is that some of this raw gas worked it its way up into your EGR valve and ignited somehow. Lucky the vehicle did not catch fire.

Any misfires that are intensified when it rains or when it gets really humid is usually the fault of a bad coil pack or packs. In rare occasions bad ignition wires or a cracked spark plug can also cause misfires also.