Tonight is being reported as the coldest night of the winter so far with temperatures expected to drop to -20 Celcius. Snow and ice have been widespread in the UK for weeks now with temperatures is Glasgow rarely reaching above freezing point, at the time of writing this at 8pm its already -9C outside. So with pretty much the entire UK blanketed in snow and ice, what’s causing it? After all, isn’t global warming, sorry “climate change” meant to be the end of the traditional winters in these parts?

Firstly, as I pointed out here, if there was going to be a negative Arctic and Northern Atlantic Oscillation (AO and NAO respectively) then we could be in for a cold winter, but I did think that the El Nino would negate the effects of these pressure differences. These oscillations represent the opposing pressure differences at certain latitudes. Basically my understanding of these setups if they are both negative at the same time, a blocking pattern occurs. This stops the usual warm wet south westerlies from reaching into western Europe and instead high pressure sits around Europe sucking in the cold air from Russia, some places in Russia sink to -70 during the winter, hence why this air is so cold at the moment! The negative AO allows the cold polar air to sink further south further chilling the air. Once this setup establishes itself it usually stays for a while, this happened in 1963, one of the worst winters recorded in the UK where it snowed somewhere in the UK everyday for over 50 days straight!

So there you go, the UK is bitterly cold because the winds are coming in from the cold east and north east instead of the usual south west, and the east winds are colder than usual due to the extreme cold air coming down from the polar region.

Originally posted 2010-01-07 22:03:01.