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 pressure. Homes are damaged by strong winds, not air pressure changes. 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. By opening the windows, you can balance the pressure inside and outside your home so a tornado will not do damage. The force of a tornado can rip through a structure, whether windows are open or not. Opening windows could actually make the situation worse. Determine your insurance eligibility now.