Life-threatening cold has gripped the American midwest recently, with temperatures diving about 20C below the seasonal average. Minnesota had a taste of the most extreme cold possible in the mid-latitudes, breaking its previous record low for January, with temperatures of -45C (-49F) recorded last weekend.
These shivering temperatures were caused by a displacement of the polar vortex, which moved southwards and delivered a blast of Arctic air. The polar vortex is a stratospheric circulation of winds that influences our weather as it strengthens and weakens during the winter.
Owing to the severe cold, Niagara Falls has been transformed into an icy vista. Mist and spray froze to form a crust over the falling water, giving the illusion that it had stopped. However, Niagara Falls has only once entirely frozen over, in 1848, when all water ceased to flow for 30 hours.
In contrast, Australia has sweltered in record-breaking heat. Adelaide reached a maximum temperature of 46.2C and Melbourne had its hottest day in five years, with temperatures soaring to 42.8C. It has been a tale of two halves for extremes across Australia, however. Hot, dry winds have fanned severe bushfires across Tasmania, whilst heavy rain has since inundated Queensland, with rivers breaking major flood levels.
Tamsin Green is a meteorologist at MetDesk
