The UK has witnessed an “exceptional” temperature for late December – but it was so early in the morning that most people slept through it.
According to the Met Office, 16.8C (62.2F) was recorded in north Scotland at 3am on Sunday in the town of Cassley.
The average night-time temperature for that area in late December is about 0C (32F).
Met Office forecaster Alex Burkill said it was the highest UK temperature recorded this late in the year.
He said: “It is pretty exceptional. We have never recorded a temperature that high this late in the month. What makes it more unusual was the temperature came at 3am.”
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The UK is currently experiencing warmer-than-average temperatures, but is yet to reach the record high for December, which stands at 18.3C (64.94F) and was recorded on 2 December 1948 in Achnashellach in the Scottish Highlands.
Meteorologists say that Sunday’s record is due to a process called the Foehn effect – which the Met Office says is “a change from wet and cold conditions one side of a mountain, to warmer and drier conditions on the other (leeward) side”.
It is said to be caused by condensation, turbulent mixing of different air currents and warming by the sun.
The most notable Foehn events in the UK tend to occur across the Scottish Highlands, where the humid prevailing westerly winds encounter high ground along Scotland’s west coast.
This results in a marked contrast in weather conditions across the country with the west being subjected to wet weather, while the lower lying east enjoys the warmth and sunshine of the Foehn effect.
Mild air from Africa pushed across the UK overnight, and as the air travelled from the South West over the UK, it rose up and lost its moisture. This meant that the other side of the hills were left with drier air.
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The Met Office said there is no indication that the warm nights will last, but Mr Burkill warned it would be a chilly end to 2019 despite the recent mild temperatures.
“There will be a bit of a north-south split to the weather,” he said.
“It will stay largely clear in the North, and the cloud and rain in the South should clear up. You will need a coat and take precautions because of possible fog in the early hours.”
The northern half of the UK is expected to be the best place to view fireworks and enjoy the outdoors this New Year’s Eve, with clear but chilly weather predicted.
Cloud and rain is expected during the daytime in the southern half.
