Mountain Weather

Living in the UK, and being ‘typically’ British, we are always looking at, and talking about the weather. Our weather is greatly influenced by the Atlantic Ocean and the Gulf Stream, a current of warm water which originates in the Caribbean. Giving the UK a relatively warm climate in comparison with other places on the same latitude. For example, London is further north than Moscow, and look at the winters they get in Russia. How would we cope, we come to a standstill if anyone even mentions the word ‘snow’.

The Jet Stream also has a major influence on our weather. The Jet Stream is, basically, a very strong wind high up in our atmosphere, and the UK is, more or less, right in it path. If the jet stream moves slightly north of us, then that usually means fine weather, as it pushes the Atlantic low-pressure systems away from us to the north and allows the warmer air from the south to assert itself over the UK. On the other hand, if it moves to the south of the UK then it allows the Atlantic low pressures to move in over the country, giving us our typical, wet and windy British weather.

Near the summit of Drum

There are many other things that influence our weather, but we will not go into those now. This is about our weather and how it can affect us in the mountains and how different it can be higher up than it is in the valleys and coast.

There are three main factors to consider: temperature, precipitation and wind. These can affect our mountain days individually or as a combination of two or all three.

In my opinion, it is the wind, that has the most influence on our day in mountains. We might be ok with a low temperature, or a bit of rain or snow, but factor in a wind with these and it can have a major effect on the conditions we might encounter. Even on a clear, sunny, summers day, a strong wind near the summits can change the temperature (wind chill) dramatically and make walking very arduous.

The general rule of thumb is that the wind speed is 2 ½ times stronger at 1000m than it is at ground level. So, a light 10mph wind down in the car park at the start of your walk would be a 25mph wind on the summit. This also doesn’t account for any gusts that might happen. A gust of 35mph can easily happen with a mean wind speed of 25mph. The mountains block the flow of air, making it swirl around and get funnelled thus increasing average and gust wind speeds.

Having a knowledge of the wind, knowing which direction its coming from and what it might be like higher up can help you plan your route and/ or make decisions on the day to alter your planned route. e.g. you might have planned on walking Crib Goch, but the forecast is showing gusts of 40mph plus. This would have you rethink your day and maybe a different route up Snowdon or maybe another scramble in a different area that is more sheltered from the wind.

The wind has a major impact on temperature. The higher we climb, the colder it gets. Temperature drops 1 degree for every 100m of elevation. Adding in any wind chill drops the temperature again.

You are planning a walk up Snowdon at the end of October. You have looked at the forecast the day before and its saying that the temperature is going to be 5 degrees. This means that on the summit (nearly 1100m) is going to 11 degrees colder, therefore -6 degrees. The forecast also says a wind of 20mph. Using our general rule of thumb of 2 ½ times faster on the summit, this will give summit wind speeds of around 50mph. With this wind speed it will make the temperature feel more like -18 degrees. Unless you have the right clothing, temperatures this cold can bring on hypothermia quickly. If its also raining, then this also adds to the issue.

The body loses heat 80% faster if you are wet. Good quality waterproofs, hat, gloves and a storm shelter, could, potentially save your life, and its only the end of October, winter hasn’t even started yet. There are more cases of hypothermia during spring, summer and autumn than during winter. People expect it to be cold in winter and go better prepared.

At lunchtime on Friday 10th June 2011, just before the start of Wimbledon and only 11 days before the summer solstice, Snowdon summit was hit by a snow storm which lasted around an hour leaving the place looking like the middle of January and caught quite a few people of guard.

Walking in strong winds can be difficult and use up a lot more energy. If caught by surprise a 50mph wind can knock you off your feet. An 80mph wind can pick you up and throw you 20 yards through the air. Not great if you are near the edge of a crag or cliff face. Plan your routes accordingly and change them if you need to. Look at more sheltered places and the lee sides of any mountains that might offer shelter.

What about the rain? We should be used to it in this country, it never stops. Especially if you live in Wales. Crib Goch has been said to have an annual rainfall of over 4 metres. But how does the rain affect our day? The obvious thing would be the lack of views and the lowering of moral, nobody really likes walking in the rain, after all, we go up the mountains to get the views from the top.

Repeating what was said earlier, if your wet, your body loses heat 80% quicker, so the rain can put a real downer on your day as well as maybe putting you or your group at risk of hypothermia. Good waterproofs are a must. Stay dry, stay warm.

We all hear that the rain makes the rocks we walk on slippy, this is correct but not entirely true to the word. The rocks are covered in lichen, which is why they all look the same colour most of the time. This is what makes them slippy. Try and stick to well defined paths where lots of footfall has prevented the growth of lichen. Sometimes it easy to spot where people have been walking, the rocks are a different colour.

During or after heavy rain can also put small stream, that you would normally just walk over or through, in spate. Some routes you have chosen might not be accessible any more, you might have to divert of your chosen route and find somewhere safer to cross, this means a bit of a diversion which can add time to your day.

Also be aware that it might be raining at the start of your walk, and you probably wont be able to see the tops of the hills you want to get to, during the colder months, this rain could be sleet or even snow higher up.

Winter on the mountains is a whole different scenario compared to the other seasons. When there is snow/ ice up there you should have the skill set and the correct kit to be able to deal with what is thrown at you. We will talk more about winter in a later post. I remember being told a long time ago, that in winter, the difference between life and death can be as little as one foot step in the wrong direction.

Snowdon from Moel Ddu

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