Wind chill in the hills and how it affects us?
The mountains are beautiful places to be, but the weather can really change the experience. Many people can, and often do, underestimate how exhausting physically and mentally (and sometimes emotionally) strong winds can be.
What is wind chill?
Wind chill is what the temperature ‘feels like’. It measures how much heat is lost from a person’s bare face when walking at 5km/h (3mph). The stronger the wind the faster the heat is taken away from the body. In the UK, a system called the Joint Action Group for Temperature Indices is used to realistically measure wind chill. It considers wind speed and humidity. This article applies to the UK mountains as other places around the world are affect by different air masses, winds, and humidity etc.
What does that mean for us?
Wind chill can have a massive impact on us as it cools our skin. Say its 10°C outside and the wind was 20mph (32km/h), it would feel like 6°C. You decide to go on a lovely walk up to a little lake (tarn, llyn, lochan in mountain speak) or to the top of a peak and that took you to 400m, it would get a bit colder right? You lose approximately 1°C for every 100m in height gained (this is called the lapse rate) and would mean that combined with the wind chill it would feel 2°C. The lapse rate does slightly vary if it is wet or dry, but for the sake of ease, 1°C per 100m is an easy number to remember.
Why is it windier in some places more than others?
Mountain weather is a complicated and beautiful beast to understand. The wind in mountains flows in very unpredictable ways. Sometimes you get a forecast that states it’s 30mph wind and you find it is stronger in some places on the hill and completely benign in others.
I have an analogy of wind, it moves how water flows in a river. Some rocks it goes around, others it goes over the top. Sometimes quickly, sometimes slowly, it’s a little unpredictable.
This is very similar (in my mind) to how wind works in the mountains. It generally can move very quickly over ridges and summit tops, and often in cols or shoulders (a dip in the land between two higher bits of land). Sometimes it can be very sheltered on the lee side of the hill (the side the wind is not coming from), however, the wind speed can dramatically increase as you get nearer the top or further away from the bottom as the wind ‘flows’ over and down.
How windy is windy?
I’ve found that a lot of people think the wind is stronger than it actually is. There’s often a bit of guess work with how strong the wind is. I sometimes hear about how someone had an ‘epic’ day out in 70mph wind (because that’s what the gusts were forecast for) but in reality, it was gusting at 45mph (still very strong). You’ll only accurately know what the wind strength is, if you took out a handheld anemometer with you (they’re £15 upwards for those interested). My personal advice is, if you are not used to walking in windy conditions to not plan to go out in more than 30mph. Above 30mph start to expect to work hard. Walking in the wind is a memorable experience. Obviously, your strength, personal fitness, weight, and experience will influence on how much wind you personally find impactful. We are all different and have different thresholds.
What does that mean for us?
Well perhaps at this point we realise that our thin windproof from a local high street shop and a little backpack carrying a small bottle of water and a chocolate bar isn’t quite going to cut it. That's why it's so important to go out in the hills prepared.
Referring to a variety of weather forecasts to get a good idea what the ‘range’ of (mountain) weather is important. This is a different forecast than the one for your nearest town or village. I personally use metoffice mountain forecast, mwis, yr.no and xc.
Your route is also an important aspect to look at. Can you easily retreat down the hill if it gets too windy? Is it easy walking? Have you thought about an exit strategy? Poles can be useful for stability however if you’ve not used them before they may be more of a hinderance than help. I’d also recommend taking the map from around your neck off and stuffing it in your jacket.
A decent windproof or waterproof is essential protection in the UK, let’s face it we really need a waterproof in the UK! As well as this a good layering system underneath. (good link here https://www.youtube.com/watch?v=tCy1gJQaJGI&feature=youtu.be) I like wearing a decent base layer and a fleece usually, and like a lot of women, I am consistently zipping and unzipping, and I rapidly heat and cool. I’m paranoid about being cold (and I really dislike it), so always have an extra layer with me. I also take gloves and a hat in my bag (especially if I know it’s going to be windy). It’s amazing how much difference those small, light items can keep you warmer. Being in the wind can be an exhilarating experience and is part of being in the mountains.
Go safe and enjoy