Here in the Midwest US - we have been affected by an air mass coming in from the Northeast - which is unusual. We usually get it from the Northwest and/or the South. It sounds like the UK is being similarly affected from air from their Northeast instead of the warmer air from their west - ocean currents.
From the Guardian:
Although it may be hard to believe, many parts of the northern hemisphere are considerably warmer than usual at the moment. Alaska and much of northern Canada is unseasonably warm for instance, with temperatures 5C to 10C warmer than expected. That still leaves the air a biting –30C (–22F) or so though. Hardly a barbecue winter.
North Africa and the Mediterranean basin are warmer than average also, by up to 10C. Elsewhere, such as across northern Europe, temperatures are coming in 5C or so colder than average. It may be called a freak cold snap, but it's actually a fairly routine distribution of winter weather, the Met Office insists.
The reason? Something called the warm-ocean cold-land phenomenon. Cold places are kept cold because there is little wind. Warm places are kept warm because of local winds coming off the warmer sea.
Like most weather systems, the cause can be traced to blocks of high air pressure, which tend to dictate wind direction.
"High pressure blocks act like heavy rocks in a stream, in the way that water has to flow around them," a Met Office spokesman explained.
Such a stubborn block across eastern Europe and Siberia has halted the prevailing westerly wind across Britain, which usually brings soggy warm air from the Atlantic. Instead, what wind there is comes down from the frozen north. With it come the freezing conditions that have seen temperatures in parts of Scotland plunge. Temperatures across many regions have failed to climb above zero during the day, while the mercury at the Met Office's Eskdalemuir observatory in Dumfries and Galloway hit –14C on Sunday, the coldest since December 1995.
The offending high pressure block seems in no hurry to move on. "There is no wind round there for thousands of miles," the spokesman said, which means the Arctic conditions over the UK look set to continue well into next week. When the weather does break, it could bring renewed chaos.
"It all depends how quickly the warmer and wetter air comes back from the west. If it charges in and meets the cold surface air then we could have 3ft of snow or we could be skating across freezing rain."