Did they specifically say that it was on account of the rain?
Could be that the school flooded.
Or a seperate issue. My school once closed, seemingly on account of the rain, because their mains water-pipe burst and was flooding parts of the school.
Could be anything else is damaged too, like their heating.
Or the weather isn't bad where YOU or the school are, but is in outlying areas, and several teachers/staff just can not get in today.