Photo of a rider casing a jump, uploaded by user "Dox" on bikemag forumsLinks to an external site.. This crash was likely caused by lack of speed, which can be influeced by a headwind. This photo was downloaded on March 14th. 

Wind

Strong winds can make Mountain Biking extremely dangerous. Strong winds can cause even experienced riders to lose balance, especially when riding technical features such as skinny wooden logs, and bumpy or rocky trail sections. 

Wind however, is most dangerous when riding trails with jumps. When a rider is airborne, they are more susceptible to the effects of wind. A strong crosswind can cause an airborne rider to be blown sideways. A mountain bike landing even a few degrees sideways can cause your tires to blow out, and/or cause the rider to completely wipe out. 

Headwinds are perhaps the most dangerous when it comes to riding jumps. A strong headwind can cause a rider to come short of the landing, which is known as a case. Casing a jump is extremely dangerous, and can result in serious injury. (Pictured above.)

Checking wind speeds on weather and mountain forecasts before embarking on a trip can help you avoid these hazards. Because trails wind in multiple directions, a wind blowing in any direction will become a headwind or a crosswind. It is best to avoid riding jumps if there are strong winds predicted in the forecast. 

This is a photo of me doing a drop, taken by my friend on August 8th 2018. The dirt on the landing is very sandy due to dry weather, which causes low traction and easier slide outs. 

Sun and Hot / Dry Weather 

Because Mountain Biking is a sport primarily done during the summer, excessive sun, hot and dry weather is inevitable.

While the sun is generally a welcomed site, riding during the sunset can be at times hazardous. Mountain biking involves looking carefully ahead for hazards and dangerous features such as drop-offs and rock rolls. At sunset, the sun is often blinding and makes it difficult to spot the trail. This can easily lead to crashes and injuries. To avoid this, it is better to ride trails shaded by trees at sunset, or to wait a few minutes until the sun is less glaring. Wearing shaded goggles also helps. 

Extensive dry weather can also be very hazardous. When trails do not get enough precipitation, the dirt becomes very dry and turns into sand, which can be very slippery. Dirt will become less cohesive as it dries, causing potholes and bumps to form in dangerous areas, such as banked turns. For mountain bikers, these hazards are almost unavoidable, but we can take precaution when riding in these conditions. Before embarking on a trip, we can check the previous week's weather, and also check mountain bike trail
directories for trail conditions. If these resources indicate dry conditions, riding at a slower speed the first few laps to inspect for potholes and gauge traction levels is a good safety precaution to take. 

Hot weather can also cause dehydration and hyperthermia. Mountain Biking is often done in heavy duty gear, such as body armour, full face helmets and gloves. Riding in this gear, in 30 degree weather, can often cause riders to overheat. A way to avoid this hazard is to be prepared with water, and to wear appropriate clothing on top of armour, such as thin jerseys. Many mountain bikers do not carry water while riding, but it is a very good idea to do so. There are very few water fountains in the middle of a mountain, so in the case of an emergency, carrying water can be life saving. 

Lastly, hot and dry weather can lead to wildfires, which lower the air quality and make it unhealthy to ride. 

Precipitation 

While sparse precipitation can help trails to become more tacky by making the dirt more cohesive, continuous and heavy precipitation causes trails to be slippery and hazardous. Rain causes dirt to turn into mud, which can easily cause bikes to slip. Rocks also become extremely slippery when wet. Most hazardous of all however, are wooden features, which can feel like riding on ice when wet. 

Rain can also cause bikes to malfunction. When mountain bike brake rotors are wet, they grip onto brake pads less tightly, causing brakes to be less effective. Water can also damage mountain bike drivetrains, causing them to shift gears slower, and causing the metal parts to rust.

Checking the weather forecast and weather maps for incoming rain clouds is useful in avoiding mountain biking on rainy days. If it has been raining recently, checking trail directories for trail conditions is also useful in determining if there are any rain-related hazards. In addition, properly cleaning bike parts after riding in the wet will insure that they are not damaged for your next ride. 

This is a photo taken by JK/Mountain Bike Action of Mountain Biking legends Wade Simmonds and Brett Tippie riding in the fog / wet on Whistler Mountain. This photo was downloaded on 3/14. 

Alpine Weather / Fog

Because mountain biking occurs often close to the peak of large mountains, weather hazards associated with mountains are present. This includes wind exposed areas on mountains and also extremely cold temperatures as elevation increases. Alpine weather is also known to change rapidly. To avoid these hazards, it is good to check alpine weather forecasts, as well as mountain weather specific websites. It is also good to know what type of mountain you are on, and whether or not it is wind exposed. If you are riding near the peak of a mountain that is much taller than its surroundings, you must prepare for strong winds. 

Fog occurs due to low lying clouds. Because mountains are often extremely tall, regular clouds can become fog. Fog causes the same hazards as sun. It can lower horizontal visibility, which is extremely important for spotting dangerous trail features and hazards. To avoid hazards caused by fog, checking weather radars for fog and cloud ceilings / floors, is useful. If you can see fog, it is best to avoid higher elevations, or to ride easier trails when visibility is low.