WATCH LIVE: President Trump speaks in Belgrade at 12:20 p.m.
Organizers are expecting between 2,500 and 4,000 people, and they're warning attendees to dress warm.
Temperatures are expected to be cold and wet. The airplane hangar where the rally is scheduled is not heated.
Airport officials recommend people with flights to catch leave earlier than normal.
A makeshift parking lot has been created at the east side of the airport at the intersection of Airport Road and Frontage Road.
Attendees will need to walk a short distance to the hangar.