|A wonderful scene to the west from Dove Crag in the Lake District|
Well, here’s a post I’m dedicating to some online friends (bloggers and ‘tweeps’) who frequently call me the ‘Inversion King’ – referencing to how frequently I get to enjoy the sight of our hills smiling above vast blankets of cloud.
You’ll have to forgive me for the slight condescending tone as I try to explain what I look for and how I catch them in ‘layman’s terms’.
|Signs of inversion around bivouac|
As most of you will know, the higher you go into the atmosphere the colder it generally gets – roughly 2c decrease for every 1000 ft of ascent. So, while it’s nice and warm in the valleys often it’s really quite chilly up on the tops.
A ‘temperature inversion’ is the reverse of what you’d normally expect. ie, it get’s warmer as you head ever higher. It’s basically a layer of warm air in our atmosphere (though there can be many) and it’s depth can vary in relation to whichever weather system is currently in place and of course terrain.
Needless to say mountains (or hills) affect how the elements behave – often in the UK it’s just colder, wetter and windier up on the summits.
To catch sight of differing types of temperature inversions, you need to consider some important points.
First of all, on clear windless nights valley bottoms cool by radiation – the heat is rising by conduction with the very near air around. A bit like steam from a kettle. The heat from the valley bottom spreads ever upwards but only through a shallow layer. As a consequence of this, the air itself close to the ground also cools.
It’s worth noting that cool air is denser than warm air and so when you have conditions like above you’ll find it very cold at ground level but quite warm up on the summits.
At dawn, the sun begins to cook the ground and over just a couple of hours or so all the ‘steam’ is released up into the atmosphere.
So, what does this mean for the likes of you and me?
Radiation fog. Valleys with misty bottoms.
|Radiation fog in the Edale Valley late September in 2010 – these don’t last long.
Couple of hours after sunrise at most.
But beware because as the sun climbs higher over the horizon these silky grey mists soon dissipate leaving behind less than ideal visibility and hazy conditions (though this tends to improve come the afternoon). So, either head up to the tops before dawn or better still, wake early and climb out your wild camp an hour before sunrise. Such sights as these are common throughout the year but more so in the autumn or winter.
Having pitched your tent late in the evening, take the time to look around. After sundown pay attention to any smoke from chimneys rising and flattening out at a given altitude or a subtle haze forming in the valleys below – these will be clues as to a temperature inversion forming for the following morning.
So, when I take a look at the weather forecast and any relevant synoptic charts – I will look to see if the wind speeds are relatively calm, will there be a clear night and how deep and sheltered are the valleys near my camp.
In effect, the weather man on the TV will explain there’s a high pressure system lounging about a given area (hopefully where you’ll be camping/walking), winds will be light and it may get cold overnight. Consequently you can be pretty certain you’ll see the sights I’ve described above.
Always, endeavour to go where the weather tells you to go – and not plan to spend the night somewhere and hope you’ll catch a temperature inversion. Note the terrain, too. A prominent peak looming over sheltered valleys would be a safe bet or a high summit looking out over a plateau.
|Warm layers in the atmosphere? Here’s one example. Pic taken from Raven Crag,
Lake District. Note the inversion and layer of cloud above.
Valleys with large bodies of water, such as those found in the Lake District for example are ripe for such scenes too – namely due to cooling water and so on.
High pressure systems generally mean calm and settled conditions and often clear skies or at the very least not much cloud at all. It’s this you need to look for on weather charts/forecasts you see. Taking along a digital barometer helps – which is why some of you will not be surprised to know why I ask for the latest air pressure readings on the likes of Twitter.
However, just because there maybe a predominant high pressure system in place doesn’t mean you won’t get any cloud.
Which leads me to the ‘daddy’ temperature inversion of them all – what most backpackers and outdoorsey types call ‘cloud inversions’.
In effect, any thick layer of cloud you’d expect to see up in the sky is now hugging the valley bottoms – and only the highest hill tops are poking out under clear blue skies.
How does this happen?
Basically in exactly the same way as I’ve described above but with a sheet of cloud. The cool condensed air of these usually fluffy monsters gets trapped below a warm layer of atmosphere. It will usually be very cold and damp in the valleys, with hardly a breeze but no precipitation.
Think of those mornings you experience with thick, cold, moist fog in the winter – there’s a good chance you’re wandering about in a cloud inversion. Head upwards a thousand feet or so and you could be in warm air under clear blue skies!
There’s a great deal more to all of this and much to consider. Weather and all it entails has many, many variables. But there is plenty of information out there to be found on this hillwalkers delight. As a general rule of thumb, if you pay attention to the descriptions above – you won’t go far wrong.
|Little Ingleborough and cloud inversion|
Statistically, it’s autumn and winter in the UK that you are more likely to chance upon these cloud inversions – or as some locals call it, ‘top clear’ days.
Why? Well, to see such sights on our modest high ground you need a number of favorable conditions to occur. North easterly cold fronts along with a high pressure system make for guaranteed cloud inversion conditions in the main. In such scenarios, a hill like Ingleborough in the Yorkshire Dales would be a good place to view one.
If the winds are westerly it can be somewhat of a contrast though. If I’m in the Peak District you’d think Kinder Scout would be good because of it’s altitude – but it’s a big mass. So, on it’s western side the pressure it would force into any incoming winds would be considerable – and in turn you’d likely get the cloud creep it’s way over the plateau and not see much at all.
So, heading for somewhere like Grindslow Knoll with it being lee out of Kinder and a little prominent will help you catch a glimpse more than at Kinder Low, say.
In north easterlies, this wouldn’t be so much of a problem due to the prevalent terrain locally.
So, there’s lots to consider.
And here’s one example of how I caught one spectacular cloud inversion (which you can see in an old video mine at the bottom of this post).
The previous few days had been generally calm, clear and cold. But one evening I noted a haze forming in the valleys around Keswick in the Lake District. It made for a fantastic sunset as it set the world alight in glorious shades of pink.
I knew then after looking at the weather forecast, that a temperature inversion was guaranteed. Winds and cold air were north easterlies and there happened to be a massive bank of cloud coming in from the Irish Sea with very little wind.
With this in mind, I set off at 3am from the holiday cottage I was staying in with my family – catching sight of the odd late night reveller in the town centre as I made my way to the flanks of Latrigg Fell.
By this point visibility was only 30 feet or so and got less as I gained altitude making my way for the summit of Skiddaw on New Years Eve.
|The Langdale Pikes surrounded by a sea of cloud.|
It was freezing cold, the ground was like concrete and progress was slow in the dark. Moisture formed on my eye lashes, my vision became blurred and morale was a little low as I finally began the steep ascent of the ‘tourist path’ up to Little Man. At times, when I stopped for a quick breather – I did think “What the hell am I doing here at 4 in the morning?!!”. Yeah, some folks out there will think it’s crazy but it makes for a good adventure with a fantastic reward.
Because not so long up this arduous and boring route, I noted a twinkle or two up ahead in the murk.
At first, I figured it was my head torch playing tricks with moisture on my eyes and carried on regardless – thinking it won’t be stars in a clear night sky.
But after catching sight of a few more sparkles up ahead, I stopped dead in my tracks, turned off my head torch and made a slow turn to look behind and then BOOM!
I was punching the air with delight!
A sheet of thick cloud as far as the eye could see on every point of the compass was just lapping below me.
It was mesmerising but I didn’t stick around for long as by now my spirits had shot off into the stratosphere and I suddenly found the energy of ten men in my legs to sprint up to the summit of Little Man – where upon my rucksack was thrown onto the ground, my cameras were set up and a gas stove was put on the go for a cuppa and breakfast.
I truly was in heaven that day and it’s one that will linger long in my memory. I didn’t want to go back down into the murk. It was quite simply breathtakingly beautiful up there and it wasn’t until an hour before sunset that I reluctantly made my way back down to Keswick!
My wife knew where I had been but was still a little annoyed I got home quite late and then spent the rest of the evening and it’s consequent celebrations asleep on the sofa.
Apparently, people shook me, shouted my name and I still wouldn’t wake. It was only when someone screamed “Fire!” that I leapt to attention like a rabbit caught in headlights.
|Synoptic charts – an important tool in your arsenal for catching cloud inversions|
I recall one week last December where conditions were perfect for a cloud inversion which would last 3-5 days in the Peak District. Unfortunately, I was sat at a desk in my previous employment (where I was to be made redundant a couple of weeks or so later) and was unable to head out and view this awesome sight.
But I did scream and shout about it to friends online – be it on forums, social networks et al – and no one paid any attention (though they always ask me for such tips).
However, photographer James Grant did note my vain efforts at encouraging folk to head out onto the tops.
He took his time, mind – thinking that with all the thick fog outside, how could there possibly be any sunshine at just a 1000 feet or so above.
I pointed out that even a modest hill such as Mam Tor near Castleton would be ideal to catch site of the full on cloud inversion but there wasn’t much time left as it looked likely to dissipate in the next day or so.
So, on the very last day James set out in his car, parked near the summit and began a cold slog up to it’s top. He admitted he nearly turned back thinking I was wrong but he figured there was no harm in pushing on that bit further to the summit of this ancient hill fort. And his reward?
The following picture looking east from Mam Tors top.
All said and done, I hope you find this information useful and you too manage to catch some of the wonderful sights you can see in our hills during the oncoming season. There is an element of luck to it all, of course -and you can’t beat having a bit of nous as to how certain weather conditions play in a given area.
For example, I’m so familiar with some hills now and how the prevalent weather tends to react it’s got to the point that given certain conditions I know full well what to expect upon my arrival, even by the hour.
But if you take the time to look into detail and gain a better understanding of how the elements dance with our hills and uplands – I’d say you’d now have an 80% chance of succeeding in experiencing a cloud inversion in some form or another….
|Dawn from the roof of all England.|
|Esk Pike looking rather majestic.|