I decided to map as much as the temperature data I had already collected for the early hours of Sunday morning (29 December) to see the size of the plume of warm air that affected a large part of the northwest Highlands. The chart below is a combination of 02 UTC temperatures from SYNOP observations, some 18-06 maximum temperatures from the Met Office WOW system, and some from the climate data loggers scattered around the area including a small hamlet called Achfary that has found some notoriety.
I notice that the Met Office have now got on board with the story. Initially they believed that Cassley had the highest overnight maximum of 16.8°C. This didn’t break the UK record, so they remained quite calm, until they rang around or interrogated their voluntary observer network and struck gold with the observer at Achfary reporting a 21-09 maximum of 18.7°C, then they and the rest of the media went into overdrive. I can’t see this temperature being rejected, and it’s very likely that this will break the existing warmest day in the UK recorded at Achnashellach on the 2nd of December 1948 even though it very likely occurred at around 02 UTC in the morning.
“Getting temperatures of 16 or 17 degrees in December isn’t all that unusual but it’s remarkable that this was during the night,” he told the BBC.Alex Burkill, a meteorologist
It’s obvious that Alex Burhill is either new to the job or never closely monitors hourly observations from places that see the foehn effect quite regularly across some parts of Scotland. When we first moved to Moray in 1987 it was not uncommon for locals to leave their washing out overnight when it was windy.
What caused it?
Many people don’t understand about the orographic or foehn effect, or what a rain shadow is. They are all one and the same thing really, and are happening all the time when you live close to or downwind of any high ground and have a tremendous effect on the local microclimate, temperature, sunshine and rainfall, depending on whether you live on the leeward slopes or not. So it’s disappointing to read as I have in Twitter how many people are dismissing this event as just another example of AGW which it is not.