While the UK is getting less cold this week in the run-up to Christmas, temperatures in the lower 48 states of the US will be taking a plunge. Over the course of the weekend, an Arctic airmass that was sitting over northern Canada, characterised by extremely low temperatures and strong high pressure, slid to the south across Alberta and Saskatchewan into eastern states of the Pacific north-west. Temperatures across these regions averaged about -23C at around midday on Sunday.
Through the week, this airmass will slowly spread southward across central states, with temperatures ranging from 10-30 degrees below average. Later in the week, the airmass will extend to the south, reaching Texas and even Florida, with some areas possibly reaching up to 45 degrees below normal. This cold airmass is likely to interact with an area of low pressure across the eastern half of the country towards the end of the week, threatening significant snowfall in states such as Minnesota, Wisconsin, Iowa and Illinois.
Over the Christmas holidays, the airmass will retreat from central states but linger across the east, with temperatures ranging from -10C to -20C.
Meanwhile, South America will experience an extreme temperature divide this week. Temperatures in Argentina and parts of Brazil will be at least 10 degrees above or below the climatological average, respectively. For Argentina and Paraguay, temperatures will be up to 20C above average, with 40C daytime maximum temperatures during the middle part of this week.
Alongside the temperature divide, central and eastern Brazil will see a lot of rain. Cumulative rainfall totals through this week could reach or perhaps even exceed 100-200mm – quite widespread for states including Rio de Janeiro, Espirito Santo, and Minas Gerais. This would mean that a month’s worth of rainfall will be falling in a single week, affecting more than 8 million people.
Heavy rain, flooding and landslides have already devastated this area of Brazil this month, with these states already recording more than 100mm. Santa Teresa, a municipality in Espirito Santo, recorded 258mm of rain from 1-3 December. Flooding meant that various municipalities declared a state of emergency with more than 100,000 people affected and 15,000 displaced.