Detailed cycling weather forecast for Col du Défens. See wind direction, temperature and rain along the entire climb and descent.

• Opens: late May – mid/late June (varies by year and snowpack)
• Closes: late September – October when snowfall returns
• Exact dates shift annually based on winter snow and spring melt — heavy snow years delay opening and early snow can force early closing. 

Rule of thumb for high French Alpine cols:

• Below 2 000 m — season often mid-April to October
• 2 000–2 500 m — late May to October
• Above ~2 500 m — often June to mid-October 

• Typically closed to traffic and cycling due to deep snow.
• Temperatures well below freezing; snow and ice make riding unsafe.

• Snow begins to melt; roads may still have snow patches near the summit early on.
• Unpredictable and changeable weather — warm in valleys, cold and snowy above.
• Pass opening usually occurs in this period. 

• Best time for cycling.
• Warmer in valleys; summit still cool.
• Weather can change rapidly — thunderstorms are common in mid-afternoons.
• Even in July/August, snow sometimes lingers near the top early in the day. 

• Often still accessible early September.
• Cooler, more rain, and increasing likelihood of early snowstorms.
• Roads may close as snow returns. 

• Temperature gradient: ~6.5 °C drop per 1 000 m of ascent → summit much cooler than valley. 
• Summer days: Warm in the valley (20–30 °C), but 10 °C or less at the summit possible, especially with wind. 
• Afternoon thunderstorms are typical in summer — plan climbs earlier in the day. 
• Weather can change quickly — cloud, rain, hail or even snow can occur, particularly outside July/August. 

• Start early to avoid afternoon storms.
• Pack layers: lightweight rain jacket, arm warmers, gloves — summit conditions can be chilly. 
• Check local road status before your ride — opening dates vary annually.