See: IN CASE(1).
{conj.} If it happens that; if it should happen that; if; lest. * /Tom took his skates in case they found a place to skate./ * /Let me know in case you're not coming./ * /The night watchman is in the store in case there is ever afire./ * /Keep the window closed in case it rains./ * /I stayed home in case you called./ * /In the event that our team wins, there will be a big celebration./ * /What shall we do in case it snows?/