Nice hot sunny days (well, occasionally), constant drizzle, torrential rain and gale force winds (more than likely…) are weather conditions that all have a huge impact on the mountain environment. In your planning you need to not only get a weather forecast, but also interpret it and decide what impact it’s going to have on your plan.
Temperature is going to impact on your choice of clothing and what spare kit you need to carry; on those few hot and sunny days you will also need to consider protection from the sun.
Wind speed and direction will often determine your choice of route: as well as having to contend with colder air temperature, high winds and strong gusts can be hazardous on exposed ridges. Notches on ridges can cause a funnel effect, as when the wind is squeezed through a narrow gap it speeds up; if you are not aware it can take you by surprise and you can quite easily lose your footing.
Rain and hail as well as being a bit miserable for your group (especially if they don’t have good quality waterproofs) can make underfoot conditions tricky. Steep ground and rocky steps can be quickly become slippery, resulting in a lot of time consuming spotting and group management considerably slowing down the day (and can sometimes necessitate a change of plans to shorten the route to get down safely).
Poor visibility can cause its own unique problems and be quite challenging, requiring good navigation skills. If you are still moving up you may want to consider re-planning your route and heading down, where visibility could be better.
Weather hazards TOP TIP
As we all know, weather forecasts are not infallible; changes to the weather can sometimes happen quickly, so having some knowledge of weather can be a big advantage in spotting indicators that predict changes. It is well worth spending time doing some homework. There are a number of good books that cover mountain weather, Hillwalking by Steve Long being a good choice.