How do you define a ‘breeze’? Or a ‘gale’?
It can often be windy – very windy – on Yr Wyddfa (Snowdon). But how good are we at judging the strength of the wind without the use of an anemometer to help us?
Personally, when looking at the forecast for the mountain, whilst the overall picture (sun/rain) is the first thing I look at, the next thing is always the wind strength and direction, as it’s an important factor regarding what conditions are likely to be like.
Certainly there have been occasions in the past when I’ve chosen not to press on to the summit because the wind has been too strong for safety. On the Pyg Track the Intersection can sometimes be an enforced turn-around point, as can Clogwyn on the Llanberis Path. (As it happens, they’re both about the same height, i.e. 750m.)
It’s tempting to think that a breeze shouldn’t be too much of a problem, and when it’s just a ‘light’ breeze (4 – 7 mph) or a ‘gentle’ breeze (8 – 12 mph) that’s true, it won’t be. (Consider the phrase “It’s a breeze”!) And on a hot day, a cooling light breeze can be a lifesaver.
But then things ramp up a bit, which might surprise you. By the mid-teens it’s a ‘moderate’ breeze, and by the time it’s in the 20s – turning ‘fresh’ then ‘strong’ – you’ll certainly be aware of it. The formal definition of a breeze actually goes up to 31 mph, and believe it or not, at this speed the wind can certainly prove dangerous.
Here’s the official definitions of a breeze:
A light breeze 4 – 7 mph 2 on the Beaufort Scale
A gentle breeze 8 – 12 mph 3 on the Beaufort Scale
A moderate breeze 13 – 18 mph 4 on the Beaufort Scale
A fresh breeze 19 – 24 mph 5 on the Beaufort Scale
A strong breeze 35 – 31 mph 6 on the Beaufort Scale
If you don’t believe that 32 mph can be a strong wind, well that’s where the definition of a ‘gale’ starts. Let’s look at what defines a ‘gale’:
A near/moderate gale 32 – 38 mph 7 on the Beaufort Scale
A fresh gale 39 – 46 mph 8 on the Beaufort Scale
A strong/severe gale 47 – 54 mph 9 on the Beaufort Scale
A whole gale 55 – 63 mph 10 on the Beaufort Scale
If the forecast is showing speeds above 32 mph (i.e. gale strength), then you need to think carefully about venturing out, and if it’s predicting speeds of over 50 mph then you really don’t won’t to be out there at all. You may have experienced being blown over by a strong wind; if you have, then you’ll know that it’s not pleasant. On the mountain the risks are magnified: whilst there are places where being blown over likely won’t do you much harm (though you could still land awkwardly and break a limb), there are other places where you stand the risk of being blown off or falling or rolling a great distance.
What’s more, winds aren’t steady. The forecasts show average wind speeds but also gusts, and it’s the latter which can prove significantly dangerous. They’ll often come out of nowhere, with no warning, and at the wrong moment. It’s very easy for a gust to catch you off balance and blow you over.
The directions of gusts can be deceptive too. Many is the time when I’ve been on the Pyg Track where the prevailing wind is coming from a southerly direction – which means that the path should be reasonably sheltered – and yet because the gusts are circling round the cwm they are actually coming from the opposite direction!
Just to complete the story, winds can, of course, exceed ‘gale’ category, to become storms and hurricanes. And the summit experiences plenty of these, but you won’t be out in these. No, you won’t.
Whilst the answer, my friend, may be blowing in the wind, remember that the wind is mostly not your friend.
A good hand-held anemometer will measure both wind speed and temperature, so can also calculate windchill.