Weather tracker: no letup in rain for western US as further deluge forecast

The US has seen various types of severe weather in recent weeks, with much of the country bearing the brunt of a winter freeze. However, California has been subject to relentless rain since the turn of the year and there is little sign of this easing over the coming week. This “atmospheric river” has brought successive areas of low pressure and exceptional rainfall to major cities on the west coast, with San Francisco seeing more than 250mm (10 inches) of rain over a 10 day period up to 4 January.

The resulting floods have already caused at least six deaths this year. Much of the precipitation has fallen as snow over the Sierra Nevada, with depths in the mountain range double what would be expected in early January.

A further surge of heavy rain and mountain snow forecast for the first few days of the week. In total, an additional 100-200mm of rain can be expected widely across California by Wednesday, and perhaps up to 300mm in the north-west of the state. Total snow depths in the mountains will probably be measured in metres by the end of the week. The torrential rains will also be accompanied by continued strong winds, including gusts of up to 60-70mph.

Meanwhile, unusual warmth is expected to affect much of eastern Asia through the course of this week. Temperatures are already above normal throughout China, but the high temperatures will spread to Japan and the Korean peninsula by the end of the week. Shanghai, for example, has an average high of 9C at this time of year, but by Friday the January record of 22.1C will be under threat. Likewise, Japan and Korea will see temperatures about 10C above the seasonal average.

The Alps have finally seen consistent and significant snowfall recently and this is set to continue over the coming week. Ski resorts have been suffering from a near absence of snow in recent weeks, caused by a combination of unseasonable warmth and rain at elevation. However, 20-40cm has fallen widely in recent days, with promising signs of further significant snow towards the end of the week.