What peak to climb and when to climb it, is certainly the most important decision you'll make while planning your trip. Three things to keep in mind are the diurnal changes, seasonal changes and the current warming planet and how these changes affect our safety and comfort on route.
- Diurnal changes in summer affect surface snow and rock. As the days heats up, the snow gets soft. That could be a good thing, facilitating descents on moderate snow slopes, allowing us to safely glissade down the slope without the need for crampons, which is faster and less tiring. But soft snow also means that bridges over crevasses are weaker and increase the risk of falling into them. Another major concern is the increase risk of rock fall. Rocks frozen into the snow and ice become loose and fall off as the ambient temperature rises and direct sunlight touches that slope. If you're below, you risk being injured by these falling rocks. In the northern hemisphere, east aspects see the sun first and west aspects later in the afternoon. Both the ambient air temperature and direct sunlight influence this diurnal heating.
- Seasonal changes influence what activity we do, ski touring and deep powder skiing in winter, ski mountaineering in the spring, and alpine climbing in the summer. There's a lot of activity overlap in the seasons, with the months of May and June seeing both great ski mountaineering and pure rock and alpine climbing. The fall season is a great time for alpine climbing without the crowds, with perfect temperatures as the planet's average temperature keeps rising.
- At the current global warming trend, earlier and warmer summers affect when we choose certain routes. The past 10 years has seen a hastened pace of glacier melting, and in general, deeper permafrost melting. We choose now to climb certain high alpine routes earlier in the season to avoid the rock fall that becomes prevalent from mid-July. The Mont Blanc Massif is a good example of this. The best time to climb the Mont Blanc would be from mid-June to mid-July. There are variants to this trend of course. The winter of 2017 saw very little early snowfall which meant the ground was not insulated from the cold winter temperatures, which helped keep the ground colder and the permafrost frozen.
So it's important to stay up to date on current conditions. Talking with people who are regularly in the mountains.