1) Cyclone cellar 2) Plains retreat 3) Refuge during violent weather 4) Weather shelter 
A storm shelter or storm cellar is a type of underground bunker designed to protect the occupants from violent severe weather, particularly tornadoes. They are most frequently seen in the Midwest (`Tornado Alley`) and Southeast United States where tornadoes are generally frequent and the low water table permits underground structures. ==Average .....
[n] - an underground shelter where you can go until a storm passes
cyclone cellar noun an underground shelter where you can go until a storm passes
a cellar or underground chamber for refuge during violent storms; cyclone cellar.