Many things can affect your day in the mountains but above all else weather has the ability to shape it the most. At best bad or extreme weather can lead to discomfort such as getting wet or sunburn. At worst however it can lead to severe accidents, casualties, or fatalities.
Checking a forecast and using it to plan your walk is essential. Sometimes it is very useful to check the weather for a few days leading up to your day out in order to get a feel for weather patterns that are moving through.
National & Local forecasts (such as BBC etc) are of some use, to give a general idea of weather in the area, but they are forecasting for valley conditions and do not represent mountain environments where the weather can be considerably different.
For example wind speed on the top of a mountain may be 2-3 x speed in the valleys/sea level which would lead to very difficult and strenuous walking conditions. There is potential to be blown over in gusts of 60+mph and high winds can make it feel a lot colder than the air temperature due to wind chill. Distances often take longer to cover when it’s windy. Also with a group long days in high winds can affect morale.
Temperature also changes with height. Unsaturated air cools at the ‘dry air lapse rate’ of roughly 1C per 100m or in wet conditions saturated air cools at a rate of 1C per 200m. If it was windy the temperature will feel colder (on both dry and wet days) due to wind chill.
There are various sources of information on mountain weather. Two of the most popular are MWIS and the Met Office Mountain Forecast
Both forecasts contain detailed and accessible information aimed at both novice and experienced mountain users. Interpretation of weather maps isn’t really required making them simple to understand and use.
So next time you heading for the hills be sure to check the mountain forecast and plan accordingly.