Big change in weather during first week of December

I have been looking with some interest at the numerical weather prediction models during the past few days. All of them have consistently been showing a cold front marching steadily eastwards across the Atlantic during 1st to 4th December. Nothing unusual in that except that the cold air behind the front originated from some very cold (for time of year) air over Arctic Canada. The effect of this will be to collapse our high pressure around 4th December and introduce a progressively cold Arctic airmass into the UK with the risk of widespread snow by the 6th. But that is not the whole story … as the cold air comes across the Atlantic, some model runs are indicating that tropical air moving north may interact with this (see previous blog on climate change) in such a way as to explosively develop a deep Atlantic depression bringing in severe gales as well as rain and snow. I’m not saying that this is definitely how it will all pan out, but I am pretty confident now that big changes are on the way next week with very cold conditions set to come down from the NW with a real risk of widespread snow. I’ll be issuing my regular forecast for Dartmoor tomorrow, so more details then.