Some brake shoes are more sensitive to moisture (which will make them grab).
First thing to do is look and see if the rubber plugs are missing from the
adjustment holes. (They are oval holes, usually at the bottom of the backing
plate, but sometimes elsewhere.) These plugs frequently get forgotten when
removed, and allow water into the brake drum.
Other alternative is to try a different brand of brake shoe...

your rear breaks?
Fix it so its not broken, if it breaks again, junk the damn thing.