The primary dangers caused by bad weather centre around the changes it causes in snow and rock conditions, making movement suddenly much more arduous and hazardous than under normal circumstances. Whiteouts make it difficult to retrace a route while rain may prevent taking the easiest line only determined as such under dry conditions. In a storm the mountaineer who uses a compass for guidance has a great advantage over a merely empirical observer. In large snow-fields it is, of course, easier to go wrong than on rocks, but intelligence and experience are the best guides in safely navigating objective hazards.
Summer thunderstorms may produce intense lightning which are attracted to the highest points on the ground. If a climber happens to be standing on or near the summit, they may now in fact be the highest point. There are many cases where people have been struck by lightning while climbing mountains. In most mountainous regions, local storms develop by late morning and early afternoon. Many climbers will often begin ascents "alpine style"; that is before or by first light so as to be on the way down when storms are intensifying in activity and lightning and other weather hazards are a distinct threat to safety.
