How Mountain Weather Changes
How Mountain Weather Changes
Simplifying Mountain Weather Knowledge
UK mountains can be pretty daring and uncomfortable if you are unprepared - especially with something as uncontrollable as the weather. Poor weather conditions can lead to hypothermia, hyperthermia, sunburn, being blown over and other exposure considerations.
Temperature at altitude
UK airflow will be the cause of different weather, however mountains and hills are big objects that are usually in the way of airflow. This means the airflow either has to go around it or over it. As the air flow rises over the tops it will lower in temperature by around 2°C per every 300m of ascent.
For example, if it's 0°C down at the coast by sea level then you can expect it to be below - 6°C on the summit of Snowdon. If you then added the windchill factor to this then the weather temperature would drop even lower. So if the wind was speeding at 50mph over a Snowdon's - 6°C summit, you can expect the temperatures to feel more like - 30°C.
Find yourself above the clouds? You’re probably in a temperature inversion; being above the clouds while everyone below is in an overcast environment. When the air is at cooler temperatures than on the hills or mountain peaks above then this will cause a temperature inversion. Top tips for finding yourself in a temperature inversion is to be on the peaks before 11am. Likewise, if the ground temperature the night before was below freezing, the clouds are low, or the weather forecast shows that sunshine is breaking through in the afternoon, then you will increase your chances of seeing an inversion like this.
if you find yourself out in the hills or mountains in lightning then there are definitely safer places to be! However, sometimes you can get caught out if the weather wasn’t as predicted. Surprisingly, an average of two mountaineers in the UK die per year due to lightning, and non-fatal strikes can occur more often.
The best way to make yourself safe in these conditions is to get off the hills and go home. but if you can’t get off of the hill then the next course of action is to find somewhere safe. Usually this would be 3m away from a wall or cliff-face, and within a zone equal to the height of that object. To increase your safety, sit on a rucksack with your arms and legs off of the ground to reduce the chance of the current travelling through the ground and hitting you on the way.
Getting Accurate Weather Information
Your average BBC weather spotlight might be great for general weather predictions across the UK and what your day will be like, but it will not be the same as the weather you are likely to encounter on the hill or mountain as all major weather news focuses on the weather at sea-level. The popular mountain ranges in the UK such as Snowdonia, Lake district and Cairngorms, will have specific weather forecasts in local hostels and outdoor shops. These forecasts will give you cloud coverage, wind speed at different heights, weather warnings, etc - and are more accurate to the conditions you may encounter. In winter conditions you can also get avalanche forecasts for the Scottish highlands. Alternatively you can use a specific mountain weather website or app - our favourite is the Mountain Weather Information Service (MWIS).
A lot of the rain that you encounter when you are out on the hills actually start as snow higher up in the sky where the air is colder - by the time it gets to you lower down where it is warmer, it has melted and turned into rain. However, in days where the air temperature and wind chill are lower on the peaks the melting process occurs much lower - this is where you start to see snowy peaks at times when the valley is snow-free.
Sometimes the weather will predict cloud free days, yet you still encounter clouds on the hills and mountains. This is due to the fact that hill and mountain terrain can form their own clouds due to altering the air flow and speeding up the formation of clouds. As the air gets pushed up over the object, the air will tumble and can form a cloud on the top of the peak, as the cloud falls over the other side it will break up as the air flow returns to normal - thus keeping lower ground cloud free.
For every 900m of ascent you make, wind speeds can double - this will usually make peaks twice as windy as the wind speeds of sea level. This is due to the air flow being forced and pushed around and over objects such as hills & mountains. This is why it is important to pay attention to mountain specific weather forecasts; if you miss judge the wind speed on mountains as being the same at sea level, you will find that ridges can become very dangerous - especially in gusty conditions.
With all of these factors above, it pays to keep an eye on weather predictions and plan your routes accordingly
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