Drivers were encouraged to remain in their vehicles during the debacle, some forced to melt snow for drinking water.
Several all-time snowfall records had been set as of Friday, with 7.1 feet (2.2 meters) falling on the city of Fujiwara in three days’ time. Fujiwara is in Gunma prefecture, a mountain region northwest of Tokyo. A number of ski resorts are located nearby.
Nearly 70 inches (178 centimeters) of Fujiwara’s snow accumulated in just 48 hours, breaking the previous record of 57 inches (145 centimeters) set in 2010.
A record 72-hour December snowfall also occurred in nearby Tsunan, where 5.7 feet (1.9 meters) came down. Elsewhere along the spine of the Japanese Alps and Echigo Mountains, a broad four to six feet (1.2 to 1.8 meters) of snow fell, establishing a number of records.
At least 1,000 cars were stranded Thursday on the Kan-Etsu Expressway, which connects Tokyo with Niigata. Some vehicles got stuck as early as Wednesday night. The traffic jam peaked in severity Thursday night, according to CNN Japan, with the chain reaction of halted vehicles spanning nearly 10 miles.
By then, snow was falling fast and furious, with conditions continuing to deteriorate as heavy bands of snow pivoted in from the northwest. Impressive snowfall rates, probably topping two inches (five centimeters) per hour, accompanied the fiercest bands.
The episode was caused by “ocean-effect snow,” similar in dynamics to lake-effect precipitation that frequents the shores of the Great Lakes. A frigid air mass blowing from the northwest over much warmer waters, in this case between 55 and 60 degrees (12.8 to 15.6 Celsius), allowed heat and moisture from the Sea of Japan to be transported inland in the form of heavy snow.
Japan’s high terrain helped focus moisture, too, concentrating it on the upslope, or windward side, of the mountains. That meant snow could fall for days at a time unimpeded, the wintry blast maintained so long as the wind fetch remained from the northwest.
Japan’s climate routinely favors hefty snowfall in the mountains. Arctic wintertime cold fronts from Siberia surge south across northeast China and the Korean Peninsula, arriving in Japan after passing over the adjacent sea. The Sea of Japan is kept mild by the Kuroshio Current, akin to the Gulf Stream; a branch of it, called the Tsushima Current, meanders west of the Japanese island chain.
At least 600 vehicles remained stuck early Friday, according to Japanese broadcaster NHK News; they were all freed by late Friday local time.
Meanwhile, another 15 to 30 inches (38 to 76 centimeters) of snow could be on the way for hard-hit areas finally beginning to dig out as the ocean effect kicks in once again this weekend. The Japan Meteorological Agency has issued warnings for heavy snow and avalanche advisories, expecting an additional “traffic hindrance due to snowfall.”