Weather is a major factor in mountaineering. Spring and summer are the preferred seasons, but are not without their own weather hazards.
At least the wind is less between May and October. In winter months, it blows at hurricane speeds (over 74mph) for weeks on end in the high Himalayas, forcing climbers to anchor themselves for the duration. In summer, winds rarely rise above 30mph. In June and July though, the monsoon brings thick clouds that cut visibility to zero.
Warm summer weather causes problems. Cold, dry snow is crusted and easy to walk on; warmer snow can be slushy and slippery. More seriously, prolonged warm weather causes water to seep through the snow, reducing its strength and grip on the rock face until it slides downslope. This is a wet avalanche, distinct from the dry avalanches in winter caused by snow piling up.
Warmth also means rockslides. The expansion of freezing water can fracture rock, but the pieces remains glued together by ice. When the ice melts in the sun, chunks of rock fall freely. These can break the bones of climbers when they hit.
David Tait, climbing with the NSPCC expedition to K2 this summer, reported that as conditions warmed up, he could hear an avalanche or rockslide every 15 minutes. One avalanche killed a Pakistani porter in another group, and there were injuries from rock strikes. It was not a storm but warm weather that forced Tait’s group back.
