Much of the US is bracing for a severe cold spell this week with temperatures set to plummet. In some places maximum temperatures are expected to drop by 15-20C over just a couple of days in contrast to above average temperatures in parts of the US earlier last week.
The rapid change in conditions is due to winds in the upper atmosphere weakening and meandering. At about six miles above the Earth’s surface there is a strong circulation known as the polar vortex around the north pole, which usually helps to keep cold air trapped there. However, late last week and early this week the circulation has been weakening and meandering, allowing a cold plume of air to be brought in from the north. Temperatures across central and eastern parts of the US are forecast to be 10-15C below average, with New York likely to see temperatures struggling to get out of negative double digits during daytime. As the cold air pushes in from the north, an area of low pressure will develop in the warmer gulf of Mexico, these two air masses will then clash across states bordering the Gulf of Mexico, bringing heavy rain and snow to areas that rarely see any. This cold spell is expected to last until the weekend, when temperatures will slowly start returning to around average.
North America’s Arctic blast is also forecast to influence north-western Europe this week. With a sharp gradient in temperatures across the American continent, the jet stream – a fast-flowing band of winds approximately five to seven miles above the surface of the Earth – is expected to intensify significantly with winds of up to 250mph possible high above the north Atlantic. This is likely to drive the development of deep areas of low pressure which will push east into Europe. As a result, a wet and windy, and perhaps stormy, period of weather is possible for countries including Ireland, the UK and France later this week and into next week. This shift comes after a period largely dominated by higher pressure which has brought dry but dull conditions with anticyclonic gloom blanketing areas with low cloud, mist and fog.
