A temperature inversion is when the normal temperature distribution of air – warm at the bottom, colder as you go up – becomes inverted or flipped upside down. This means you have a cold layer of air trapped at ground level, overlain by warm air.
Because it looks amazing if you can get above the cold air! In the right conditions, temperature inversions in Scotland lead to a thick layer of mist clinging to the ground. If you are lucky enough to be standing on a hill when it happens you can be treated to incredible vistas of a sea of cloud, with island-like mountain tops rising out of the mist. Or, if you enjoy misty mornings for photography or just sheer ambience, then head lower down.
To be clear, we’re talking about ground inversions here – when the cold layer of air is trapped against the ground. Inversions can happen at all different heights in the atmosphere, but it’s when it happens at ground level you typically get spectacular results.
Ground inversions usually happen on a cold, clear night. Clouds can trap the heat next to the ground, but when it’s clear there’s nothing to stop the heat built up during the day from radiating away. Because the ground cools down rapidly, the air in contact with it does as well.
If the temperature of this cooling air falls to below the ‘Dew Point,’ then water vapour will condense in the atmosphere, producing mist. If the dew point is too low or the temperature doesn’t drop far enough, then the inversion doesn’t do anything more than make it a bit colder in the morning.
It’s the temperature below which water vapour will condense. So, if the dew point is forecast to be 7 degrees, and the temperature is forecast to fall to 4 degrees, then you should get mist. The more humid the air, the higher the dew point, and the more likely it is to get mist if the temperature drops.
Spring and Autumn are the times when all the necessary conditions are most likely to converge. In Spring the temperature during the day is increasing but the nights are still cool. Autumn days are relatively warm and humid after the warmth of summer, and clear nights are cold. That gives you the magic ingredients of humid air and a plummeting temperature to produce mist over a wide area.
During spring and autumn, it’s almost a safe bet here where I live in the Cairngorms National Park that any clear night will lead to a spectacular temperature inversion the following morning. As a passionate landscape photographer, these mornings are precious to me, and I hate to let one slip by unexplored.
Early starts are key to making the most of an inversion, because once the sun comes up and starts warming the atmosphere it’s usually just a matter of time before the mist burns off. The key thing is to keep a close eye on the weather. If it’s forecast to be fine weather for a few days, with cold nights, then I’ll plan to be up early and in position with my camera for sunrise. Sometimes the mist does not appear until after the sun comes up, so if it’s clear when you head out then keep the faith.
If you’re up for it, then an early start in the mountains on these days can lead to memories that will last a lifetime. Of course, temperature inversions and the awe-inspiring sights they bring can happen at any time of year – it just depends on the conditions of temperature and humidity
Spring weather is mild, but the days are lengthening and consistently drier. The landscape is buzzing with life and colour, with flowers blooming and bustling wildlife.Find out more
Summer promises long days, pleasant temperatures, and festivals galore. The countryside transitions from vibrant green to breath-taking purple as the heather blooms.Find out more
Autumn is a time of colourful landscapes and glowing skies. Witness some of Scotland’s most exciting wildlife spectacles and taste flavours unique to our autumn months.Find out more
If the conditions are right, Scottish winters are the epitome of ‘winter wonderland’. Crunchy snow underneath your boots, sparkly fields, and the most beautiful night skies.Find out more
Temperature inversions become even more exaggerated and spectacular in mountainous terrain. Cool air is more dense and heavy than warm air, so it will flow down the mountainsides and become trapped in valleys and hollows just like water in a pond. This can mean that the mist can hang around for hours, but if you’re lucky enough to be on the top of that mountain then you can enjoy warm air, clear skies and an incomparable view. As the cold air flows down the hillside you can sometimes also watch the mist flow and ripple across the hills, like water passing around stones. If this is what you want to see then head somewhere with plenty of hills.
At lower elevation, the mist will be most intense around still bodies of water such as lochs and slow-flowing rivers. Because the water has had all summer to heat up, it’s warmer than the air above and will gently evaporate, appearing to steam, and thickening the mist still further. In my opinion, there’s nowhere better to be than beside a calm loch on a day like this, just as the air finally starts to warm up again. There are a few brief minutes of magic when the mist is thinning and the sun illuminating it when the whole world is suffused by silence and golden light.