An atmospheric river has been under way through the weekend, pummelling northern and central parts of California with spells of wind and heavy rain and hill snow, and is forecast to continue into Wednesday.
The weather system, locally called the Pineapple Express, is set up by low pressure situated to the north-east of Hawaii, which propels moist tropical air from Hawaii and across the Pacific Ocean on blustery westerly winds. The result is a stream of heavy precipitation piling into parts of the west coast of the US, falling as snow down to about 1,200 metres (4,000ft) with rain at lower levels. A cumulative total of up to 500mm (20in) of rain is expected to have fallen by Wednesday, while up to 1.8 metres (6ft) of snow will be possible in mountainous areas. Subsequently, there has been a risk of flooding.
Farther north in Canada, an arctic air mass has brought strong katabatic winds to parts of British Columbia. Sometimes called a Squamish, these north-easterly winds funnel cold air through fjords and towards the west coast, strengthening in the process, gusting up to 75mph. The combination of strong winds and low temperatures brought the risk of wind chill values of -20C to -25C from Saturday, and these are expected to continue into Tuesday, potentially into Wednesday. A warning for frostbite and hypothermia – which can occur in minutes in these conditions – is in place.
Areas of north-east Queensland in Australia, particularly around Townsville have been under weather and flood warnings through the weekend, which are continuing into early this week.
Torrential and persistent rain through the course of the weekend and early this week is expected to bring 1000mm of rainfall, with up to 300mm of this falling within six hours. This rainfall has caused severe floods, with river levels forecast to rise to their highest in more than 50 years, and possibly breaking records. One person has already died as a result of the floods and thousands have been evacuated.
The severe rainfall is caused by a very slow-moving low pressure to the north of Australia, which drives a warm and moist south-easterly flow from the coral sea. Meanwhile, South Australia and Victoria are experiencing an intense, but brief heatwave with temperatures expected to reach about 40C in Adelaide on Monday and Tuesday, which is more than 10C above average. The temperature in Perth is also expected to peak at over 40C.
