They can be hidden in heavy rainfall. Downward-bulging clouds mean tornadoes are on the way. This may be the case, but many of these clouds are not associated with tornadoes and may be completely harmless. Tornadoes cause houses to explode from changes in air pressure. Homes are damaged by strong winds, not air pressure changes.
Tornadoes always come from a thunderstorm.
This is usually true, but thunder and lightning are not prerequisites for tornadoes. Tornadoes can also be spawned by hurricanes, with or without lightning. Tornadoes cannot cross water. Waterspouts are a type of tornado that actually form on water. Tornadoes that form on land can cross bodies of water such as rivers and lakes.