The Tour de France is perhaps the most arduous sporting event on Earth, a nearly month-long journey across multiple countries, 500 cities and up and down multiple stretches of mountain ranges in the French Alps, Pyrenees and Massif Central.
The weather invariably will come into play at certain points during a race, especially when some tour stages can be greater than 100 miles in length. The conditions at one point in the race could inevitably change during the same stage.
"The weather can change pretty drastically from day to day," AccuWeather Meteorologist Evan Duffey said. "Some of the start locations for courses are quite far from each other. Proximity to the ocean or the mountains is important, as is the change in elevation depending on where the riders are located."
Overall, this year's competition covers a total of 2,082 miles (3,351 km) over 21 stages.
Belgium's Greg van Avermaet, wearing the overall leader's yellow jersey rides in the breakaway on a gravel road during the tenth stage of the Tour de France cycling race over 158.8 kilometers (98.7 miles) with start in Annecy and finish in Le Grand-Bornand, France, Tuesday, July 17, 2018. (AP Photo/Peter Dejong)
The weather can shape a race in many ways. One of the most common threats that weather can pose is rain causing roads to become slick, according to Guillermo Rojas, director of marketing and communications for USA Cycling.
"These 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 be a little dangerous," Rojas said.
Rojas added that the painted lines on the roadways can become especially slick, so riders will look to avoid them at all costs.
Climbing up a mountain can be rigorous enough, 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.
Heat loss can be maximized by appropriate clothes (bright clothes) and by favoring heat dispersion by water convection, said Professor Xavier Bigard, the medical director for Union Cycliste Internationale.
Sprinkling water, especially on the head, is an efficient mean for heat loss that could be used during the race. But the key determining factor of performance under hot climate is the availability of water during the race; the maintenance of fluid balance is clearly a key issue for the performance of riders, according to Bigard.
"During uphill cycling, the role played by convection is markedly decreasing, and heat loss results mainly from sweat evaporation. Such situation is at risk of body fluid loss, dehydration and failure of performance," Bigard said.
Tour de France teams consist of eight riders as well as separate team vehicles that carry different clothing, such as rain jackets, and other necessities so the teams are prepared for variable weather.
Luxembourg's Bob Jungels speeds downhill during the tenth stage of the Tour de France cycling race over 158.8 kilometers (98.7 miles) with start in Annecy and finish in Le Grand-Bornand, France, Tuesday, July 17, 2018. (AP Photo/Peter Dejong)
Often, the teams will ride tightly bunched together in diagonal line in an effort to shield the rider who has the best time from the wind.
The main grouping of all the riders (about 176 in total) in the Tour de France is known as the peloton. Strong crosswinds can often wreak havoc in the peloton and cause the pack to become separated.
According to Velon, an engagement platform for cycling fans, crosswinds can turn a simple stage into a complicated and dangerous one.
Teams will often use the winds as a way to outmaneuver their competitors.
"If a group or an individual attacks in strong winds, it can be impossible for the chasing riders to catch them," Velon states.
"Crosswinds can turn what should be a very straight forward stage, like a flat sprinter's stage, into a major tactical battle," Duffey said. "Crosswinds can 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," Duffey said.
In the event that weather becomes too extreme, it's not uncommon for race organizers of large stage races to scale back portions of the course to minimize the potential health effects of weather conditions. This happened in the 1996 Tour de France when the ninth stage was reduced from 109 miles (176 km) to 28 miles (46 km) due to snowy climbs.