Believe it or not, under specific weather conditions you can actually walk above the clouds. This is known as a ‘cloud inversion’ and can mainly be spotted during Autumn and Winter. I saw my first ever cloud inversion from Helvellyn in the Lake District, and I felt on cloud nine – pardon the pun. It was truly phenomenal! From that day, I became hooked and began studying these as I was determined to spot more in the future.
So you may be wondering, how does a cloud inversion form? Well, these occur when colder air gets trapped below a shield of warmer air. This creates a magical effect of fog sweeping over the area. Under usual conditions, the general rule is that the temperature drops as you gain height. However, on occasions, this general rule is reversed and a cloud inversion is formed.
In the UK, there are two main types of cloud inversions, the most common being nocturnal inversions. Nocturnal inversions occur mainly under high pressure and settled conditions, which usually go hand in hand. They mainly occur in the winter half of the year due to the long nights. The conditions to look out for are high pressure, little to no wind, clear skies over night and more likely to occur in hilly mountainous terrain. The cooler air from up on the hills sinks into the valleys due to its density which then allows the less dense warmer air to be on top of the cooler air, creating a cap. As the air temperature quickly drops due to the clear skies and then reaches its dew point, the cooler air then condenses and this fog/cloud is then trapped under the warmer air creating a flat top.
The other main type of cloud inversion is called a Subsidence Inversion. It is called a Subsidence Inversion due to high pressure system having descending air which warms as it does so. These inversions occur when high pressure moves across Britain mainly from West to East. When the high pressure centre is centred just to the West of Britain, cooler air is drawn from the polar region to Britain. Due to the nature of the settled conditions which accompany high pressure systems, the layers of air from the atmosphere are less likely to be mixed. As the high pressure centre slowly moves across Britain, the descending air is at its strongest. If the high pressure centre remains in place for a few days or more, the layer of warmer air gets lower and lower, and sometimes descends to the height of the highest mountains in Britain. This means when climbing your favourite peak, you are likely to ascend into warmer air and if enough moisture is present in the lower cooler layer, cloud may be present. The moisture mainly occurs and gets added to the mix as the high pressure moves East across Britain which creates a change in wind direction, bringing more humid air from mainland Europe. Similar to the first type, the warmer air creates a capping layer which limits the height of the cloud top enabling you to be above the cloud. There are other types of cloud inversions but these are the main two.
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