The comparatively high temperatures over the higher mountain tops across Scotland were swept away yesterday by colder air that advected down in the northeasterly flow. Curiously it was not the cold front that was the demarcation boundary between mild and cold which broke the inversion, but colder air well in advance of it yesterday afternoon blowing in from the east. The thermograph from the Cairnwell saw the change at around 11 UTC when the temperature went sub-zero. It took another nine hours before the effects were felt on Aonach Mor to the west, but just after 19 UTC the temperature there fell by eight degrees in a single hour. We’ll never know what happened on Cairngorm because the Met Office in their infinite wisdom disabled the temperatures and dewpoints being reported from the SIESAWS the day before, when they mistakenly thought that the temperatures were spuriously high (possibly caused by very light winds), which shows you how much they know about mountain weather. So if in the remote chance anyone with a care is listening down in Exeter do us all a favour and please turn them back on and cancel the call to the techs the sensors are perfectly fine.