Each airline will make their own decision to cancel a flight based on things such as weather, if an airport is open or closed, crew, mx and etc. Keep in mind that if a flight is cancelled, that means that aircraft can't continue on to it's onward location thus leaving two groups of pax stuck (those on the cancelled flight plus those waiting for the their flight) and when it comes to an airline that flies both domestically and internationally, unless there are "issues" at international locations (i.e. snowmageddon and/or volcanos in Europe), international flights are generally the last to be cancelled