The most common threat that weather poses on the tour de france is rain that causes roads to become slick.
The cyclists are gonna be finishing most of the stages sprinting and they're sprinting close to 40 mph. So under wet, slick conditions, it could become a little dangerous.
Also the painted lines on the roadways can become especially slick, so riders will look to avoid them at all costs.
The heat can also take a toll on the riders and if it gets too hot and the riders are climbing up a mountain which can be rigorous enough during cooler weather but on a hot, humid day, it can become even more grueling.
A rider's performance in these conditions is strongly dependent on maintaining efficient heat loss and water replacement.
Crosswinds can also cause trouble for the riders in the tour de France and can turn what should be a very straight forward stage, like a flat sprinter's stage, into a major tactical battle.
The Crosswinds can also force breaks in the field on a stage that all of the favorites usually finish with the same time in the peloton.
Teams that are unprepared for a crosswind can see their general classification contender lose significant amounts of time.