荒天のため運動会は中止になったことを説明する時は、
Due to severe weather, Sports Day has been cancelled.
Due to bad weather, Sports Day will be cancelled.
Due to~ :~のため、
Sports Day:運動会
cancelled :中止
もしも延期になった場合は、
Due to severe weather, Sports Day will be suspended until further notice.
Due to severe weather, Sports Day will be postponed until further notice.
suspended:延期
postponed:延期
until further notice:次にお知らせするまで
I hope this will help you.
お役に立てば嬉しいです。