The invitations have been sent through Facebook. The rules are set. Police and medical responders are ready to go. When a whistle blows Saturday afternoon, University of Wisconsin-Madison students will begin pelting each other with snowballs in a fight they hope will go down in history. More than 3,700 students at Michigan Technological University in 2006 laid claim to the largest snowball fight, according to the Guinness Book of World Records. Organizer Mike Basak, a UW-Madison freshman, said Saturday's snow showdown would likely beat that record, though he's decided not to bother with the hassle of submitting it to Guinness. More than 4,000 people are members of the event's Facebook group, and word continues to spread as rival dormitories get ready to rumble in the center of campus. “Once the whistle blows, let the chaos ensue!” Basak said. The ground rules are simple: No throwing at cars. No throwing at buildings. And don't hit innocent passers-by. Some suspect poor timing means the Michigan record might not fall. Temperatures in Madison were forecast to remain in single digits Saturday. Wisconsin's men's basketball team plays at Illinois at the time of the fight. And although snow is everywhere on campus, it's the powdery kind that's hard to pack. Still, school officials are prepared for the event. UW-Madison spokesman John Lucas said in a statement that officials would monitor the event, which he noted wasn't university-sanctioned. “We want students to be able to enjoy winter and have fun, but safety is also an important priority,” he wrote. The Dean of Students' office recruited a student group of volunteer emergency medical technicians to be on the scene. One of its organizers, Katie Egan, said members would be ready to treat injuries such as bleeding and hypothermia and call 911 if needed. Police Sgt. Jason Whitney said officers were getting in touch with the organizers and would be ready Saturday. Patrolling snowball fights was something new for his force, he said. As for judging a winner, Basak said, that was not the point. “It's just a bunch of chaos until it all kind of dies down,” he said.