From deep cyclonic to anticyclonic, the wild swings of autumn! Storm Amy and her record low pressure and wind speeds seem like a distant memory since a powerful area of high pressure steadily built in and anchored itself over the UK.

As is often the case during autumn, we’ve found ourselves parked beneath a strong, dominant 1036mb high. Having drawn moisture in underneath from the subtropics, it’s been anything but sunny for the majority, at least below 2-2,500ft anyway.

This is a classic autumn-time ‘capping inversion’ setup with moisture in the form of cloud, fog and drizzle trapped beneath a lid of dry, sinking, stagnant air.

The below charts show this high containing some pretty mild air at approximately 5,000ft.

The air mass considerably warmer than normal at 850mb for time of year.

Due to this cap being relatively low within the atmosphere, hills and mountains, especially over N/NW England and the Highlands are ABOVE the cap and within crystal clear skies and fairly warm sunshine. It’s the opposite below.

The view at Glencoe Tuesday (14th October) afternoon shows this beautifully.

Those hill walking have enjoyed those spectacular views looking down over the thick blanket of cloud.

Last weekend saw some big contrasts with warmest temps at height, coolest below.

The 20.4C recorded at Great Dun Fell was not only the UK hot spot but it was this site’s warmest October day also!

Interestingly while air on top of an inversion can warm by daytime, it doesn’t cool so much by night and so we get the situation where high ground is considerably warmer than low ground, especially overnight.

Big contrasts in humidity, dew point and temperature.

Check out the below humidity chart 09.50UTC on the 14th October. Within the cloudy, misty, murky low levels (underneath the lid), especially within valleys and glens where there’s chance for mixing, humidity was 100%, a saturated atmosphere but above the inversion, moisture levels were desert-like! Take Aviemore, 99%, Cairnwell 15%!

At 08.50 UTC on 14th October, note the -14C dew point at Cairnwell, elevation 650m compared to surrounding lower elevation sites.

At 05.50 UTC on 14th October, Aviemore and Cairnwell both under clear skies was reporting 4C vs 13C respectively! A good example of the inversion and warmth aloft.

Cairngorm Summit, elevation 1,245m and only 12 miles away from Aviemore, like Cairnwell, reported a balmy 13C at the same time Aviemore was 4C.

Sunday 12th October saw some remarkably low humidity, dew points and fluctuation over the UK’s mountain tops.

Between midday Sunday and 8am Monday, Cairngorm Summit’s temperature hovered between 8-12C but remarkably while both temperature and dew point we’re similar (meaning in the cloud), there was a sharp drop from 8 to -28C in DP (within 3 hours), a result of the inversion level plummeting and the summit suddenly in the clear, dry air.

At 06:00 on the 12th October, Great Dun Fell reported a relative humidity of 4% and dew point of -27.6C!

At 21:00 on 12th October, Cairngorm Summit was reporting an air temp of 12.1C, relative humidity 8%, dew point -20C.

Unfortunately, there’s no Met Office confirmation on this but I did a search of UK’s lowest humidity on record and here was the results…

The lowest humidity recorded in the UK was 6% at Great Dun Fell on March 2, 2011, and 6% in Glasgow in 1984. Another source mentions even lower figures of just 4% over the Pennines in October 2025 during an anticyclonic gloom event. These low humidity events are more common on higher ground in Scotland and northern England, where air from above the cloud layer is drier. 

• 6% humidity: Recorded in Glasgow in 1984 and at Great Dun Fell on March 2, 2011. 
• 4% humidity: Recorded over the Pennines in October 2025 during a high-pressure spell. 
• Where it happens: Primarily on higher ground like the Pennines and Scottish Highlands, where the air is less affected by ground-level moisture. 
• Why it happens: During anticyclonic conditions, higher ground can be above low-lying cloud, into clearer and drier air.