A bitterly cold Arctic airmass, which has gathered across Canada in the past week, has spread southwards into the US over the weekend. Having already allowed temperatures to fall as low as -40C in northern Canada, this cold airmass combined with moisture-laden air from the Gulf of Mexico to become a major winter storm named Blair, bringing disruptive winter weather across a wide area of the US.
Over the past 24 hours, Blair has brought significant snow accumulations as well as dangerous ice storms and freezing rain across a wide area, from the central Great Plains in the west, across the Mississippi and Ohio Valley, and on to the east coast.
It is forecast that up to 2cm of ice could accumulate on surfaces, leading to power outages and tree damage. The cold Arctic airmass is then expected to continue to push southwards across much of the country through this coming week, reaching as far as the Gulf Coast.
The underlying cause of Storm Blair and the Arctic airmass intrusion is a continuation of the disturbance to the polar vortex, a huge three-dimensional ring of powerful winds typically 12-30 miles (20-50km) aloft that spins around the north pole. Disruption to its usual pattern means it is going to be moving well south across the continent in the coming days, dragging the cold air with it.
The strong and active polar vortex so far this northern hemisphere winter has been the main cause of temperatures as low as -55C in Siberia, and now the most intense part of the vortex has shifted to North America.
In contrast, south-east Australia has been suffering from an intense heatwave in recent days, with increased bushfire risk and fire bans for a growing number of residents across the state of Victoria. It has been a particularly severe bushfire season so far. Last week, Victoria’s Grampians national park suffered a huge blaze with farms and homes affected.
Temperatures on Sunday reached about 45C in parts of Victoria, while Melbourne, the state capital, recorded a 38C. Total fire bans have been enforced across three state districts, where authorities have deemed the danger of fire as “extreme”. Other parts of the country have also been suffering from heatwave conditions, including New South Wales, Western Australia, and Tasmania.
The bushfires are a reminder of the catastrophic 2019-20 summer, when 33 people were killed in fires that devastated an area the size of Turkey.
Delhi in India is being affected by several days of thick fog with zero-visibility conditions having been reported for three consecutive mornings. This has led to hundreds of flight cancellations at both the city’s main airports, as well as delays and cancellations to scores of train services. Visibility has been at its worst early in the mornings, but the international airport at Palam, south-west of the city centre, recorded a nine-hour spell with zero visibility on Saturday. Air quality is said to be “very poor” in the Indian capital.