Weather tracker: Cold air over warm waters brings heavy snow to Japan | Japan

Heavy snow fell across northern Japan on Thursday, with the prefectures of Hokkaido, Aomori, Yamagata and Niigata particularly affected. Accumulations of 20-30cm over a 24-hour period were recorded across the affected areas, with local totals of more than 30cm near Aomori City.

The snowfall was a result of heavy showers generated by a cold airmass moving in from the north-west across the relatively warm waters of the Sea of Japan. This resulted in warming of the lowest levels of the atmosphere, leading to rising motion and convective shower development caused by the increased moisture. Ascent was further aided by the mountainous terrain across northern Japan.

Further heavy snow is expected from this atmospheric pattern over the coming days. Additional snowfall of 20-30cm is possible in places, with southern parts of Niigata prefecture expected to see the greatest totals.

Heavy snow also appeared downwind of the Great Lakes across eastern Canada and the north-east US on Thursday, and is expected to continue over the coming days. Snowfall here will result from a similar process to that seen in Japan, with cold air blowing across relatively warm lake waters. Snowfall will be focused in relatively narrow bands, with snow accumulation between Friday and Sunday of 30-40cm to the east of Lake Ontario. Totals of 10-20cm are possible downwind of Lake Huron and Lake Erie.

Elsewhere in the US, low pressure moving into the Pacific north-west will bring a period of heavy rainfall and risk of flooding to western Oregon. Rainfall totals of 80-120mm are expected across the Oregon Coast Range between Friday and Saturday, with 60-80mm possible across the western slopes of the Cascade mountains.

As the disturbance responsible for the heavy rain in the Pacific north-west moves inland through the weekend, it is expected to result in a period of unsettled and dangerous weather across central parts of the US on Sunday and Monday. Low pressure is expected to track eastwards from Oklahoma to Tennessee on Sunday, bringing a risk of severe thunderstorms across parts of Arkansas, Louisiana and Mississippi to its south and a broad area of heavy snow and freezing rain to its north.

Snowfall totals of 15-30cm are possible in a band extending from Kansas to West Virginia, with strong winds leading to the potential for blizzard conditions at times. In areas experiencing freezing rain, ice accumulations of more than 0.5cm are possible, leading to a risk of power outages and dangerous driving conditions. As the low clears to the east into next week, an Arctic airmass will spread across the eastern half of the US, with temperatures significantly below normal across a large part of the country.