This month, as the weather takes a distinctly autumnal turn, blogger and keen hiker Phil Thomas explains how to track down the elusive but, oh so beautiful, cloud inversion…
Have you seen those amazing photos where people have climbed your favourite mountain in Snowdonia and found themselves standing in bright sunshine, with clouds nestled in the valleys below? This weather phenomenon is known as a temperature or cloud inversion. Most of the time you’ll just chance across these conditions by luck. Yet with a little knowledge of weather patterns you can increase your chances of catching one.
The best time of year for cloud inversions
Forecasting cloud inversions is extremely difficult, but one of the easier statements to make is that they tend to occur most in autumn and winter. That’s because one key ingredient of a cloud inversion is the presence of colder air. During warmer days they are far less likely to occur – but by no means are they impossible. If you’re frequent hillwalkers in the UK you’ll know that there can be some surprisingly cool days in spring and even summer.
So if you’re hoping to see a cloud inversion, make sure you’re prepared for an early start during the shorter days of the year, and be prepared to have to navigate your way through cloud and mist at lower levels.
Weather conditions to look out for
We’ve mentioned cold air, so the best weather conditions in the winter months arrive with colder airflows, often associated with high pressure (anticyclones for the meteorologists among you). Typically, winds come from the north or the east and need to fall light for cold air to become trapped in valleys. In “normal” weather conditions, the greater the height, the colder the air and the ground. With a temperature (or cloud) inversion, warmer air at higher levels traps colder air beneath it. Hence the term “inversion.”
There is another caveat. In order for the cloud and mist to form, you need moisture. So the very best time for cloud inversions to form is after a few days of cold, still conditions, but with a change in weather to milder, wetter conditions imminent. In practice, if there has been a period of cold, calm weather, with light winds from the north and east, but the wind is due to swing to a wetter, more westerly direction, that’s the ideal time to find your cloud inversion. Tricky, yes. And there are no guarantees. But by following the weather forecast carefully, you can increase your chances of experiencing that magical cloud inversion.
Terrain plays a part, too
Photographers who “chase” cloud inversions will also advise that terrain plays a role in the likelihood of cloud inversions occurring. The higher the peak, the better the chance you have of experiencing one. On many days the inversion “point” (sometimes referred to as a capping layer) is well above even our highest mountains, so even with perfect conditions you won’t experience a cloud inversion from any of our summits.
Because still air is required, it helps that the valleys are as sheltered as possible. This isn’t always the case for some valleys. An east-west valley opening to the sea, for instance, may have too much of a breeze for clouds to form at low level. The presence of a lake, meanwhile, provides tailor-made conditions for moisture to condense. So sheltered valleys with a river or lake will be your best bet.
Be prepared for misty walking
It’s worth repeating that to experience a cloud inversion you will often need to walk through that cloud to reach the clear, sunny skies higher up. Make sure you are comfortable navigating your way through poor visibility. Don’t choose a challenging scramble for your cloud inversion hunt! Remember, conditions for cloud inversions may not last the day. The earlier you can reach your summit, the better.
Happy cloud inversion hunting!