For the third time in just over a month, an extreme ocean-effect snowstorm dumped more than six feet of snow on Japan, crippling travel and dropping visibilities to near zero. The storm, which peaked during the weekend, reportedly trapped more than 1,200 drivers on the Hokuriku Expressway on the island of Honshu.

The episode is the latest in storms that have pummeled Japan, including a record-setting snowstorm in mid-December that dropped seven feet of snow and stranded 1,000 motorists in a 10-mile traffic jam.

Meanwhile, another round of significant snowfall is likely in the mountains of central and northern Japan late this week into this weekend, with three to five more feet on the way for some.

We’ll file this one under the heading “just when you think it couldn’t get any worse.”

Extreme snowfall stacks up to record depths

Along the central west coast of Honshu, several locations recorded astronomical snowfall amounts because of a synergetic combination of cold air and moisture. At Takada, on the west coast in Niigata prefecture, more than six feet of snow fell in a three-day period. That would equate to an inch of snow falling every hour for 72 hours straight.

Hijiori, the recipient of several bouts of heavy snowfall over the past few weeks, had 10 feet of snow on the ground Sunday evening, then added another foot early Monday. The Japanese News Agency reported some areas along the west coast have already seen up to nine times the amount of snow they normally get at this point in the winter season.

To add insult to injury, this most recent storm also produced winds up to nearly 100 mph as it crossed the nation. The huge snowfall totals have also raised concerns of avalanche potential across the region.

A case of meteorological deja vu

If you think you have heard this story before, you are correct. Locations across the snow country of Japan have been hit by two other major snowstorms this winter, each producing more than seven feet of snow.

In mid-December, a multiday storm occurred across the Japanese Alps and the Echigo Mountains, dumping four to seven feet of snow. A couple of weeks later, the new year was rung in with yet another major snowstorm as several locations were hit with an additional four to seven feet.

Japan has a reputation as one of the snowiest populated locations on the planet; it’s well-deserved. In fact, tourists from around the world flock to the Tateyama Kurobe Alpine Route, which weaves through the Hida Mountains in central Honshu, to see the snow corridor that builds each winter season.

A factory for extreme snowfall

Japan is located off the Asian continent, separated by the relatively warm waters of the Sea of Japan. During the winter season, the warm Kuroshio ocean current keeps water temperatures in the 50s to low 60s. At the same time, some of the coldest air in the Northern Hemisphere is regularly transported east on prevailing winds out of Siberia, crossing the Sea of Japan.

As that frigid air crosses the mild waters, it’s heated and infused with a tremendous amount of moisture; the air rises and condenses to make clouds and snow, its moisture eventually deposited downwind across Japan as snow. This process, known as ocean or sea-effect snow, is just like lake-effect snow, which occurs off the Great Lakes each winter.

The mountain ranges of Japan help to induce upward rising motion in snow clouds, resulting in a very efficient snow-making machine.

What makes ocean-effect snow so prolific?

Ocean-effect snow in the Sea of Japan is often much more intense and exists on a bigger scale than what we encounter from the Great Lakes. Unlike most Great Lakes snow events, the structure of these ocean-effect snow bands isn’t always parallel with the prevailing wind direction. Sometimes the bands can be oriented diagonally or even perpendicular to the wind — but they still result in lots of snow.

The secret to these epic snowfalls isn’t just how heavily the snow comes down but the duration of the storms. Across most of the world, once the main low-pressure system responsible for a snowstorm moves away, conditions generally improve. But in the case of Japan’s ocean-effect, as long as there’s a supply of cold air crossing those warm waters, snowfall can continue. That’s what happened again over the weekend, with snowfall persisting up to three days in spots.

If the wind is consistently blowing from the same direction, snow bands parallel to the wind can park themselves over the same area for hours or days, “flooding” spots with constant heavy snowfall. It’s similar to “training thunderstorms” in the United States, or repeated, stalled bands of heavy downpours that can induce flooding in the warm season.

Weather radar showed very heavy precipitation rates, suggesting some tall, bubbling storm clouds. The storms also were producing thundersnow.

But what sets Japan’s snowfall this winter apart from other years? A combination of factors has been at play.

The winter has been colder than normal across eastern Asia, including northeastern China and the Korean Peninsula. That cold air is instrumental for fueling ocean-effect snows.

At the same time, several low-pressure “storm tracks” set up a favorable wind flow for long-duration cold temperatures over the waters to maximize snowfall potential for Japan during all three events.

Meanwhile, there’s no immediate end in sight to the record-breaking snows. The Japan Meteorological Agency’s latest one-month snowfall forecast suggests odds of near-normal snowfall for the coastal areas of Japan — so there’s certainly plenty more opportunity to add to an already amazing snowfall season.

Matthew Cappucci contributed to this article.

Tom Niziol recently retired as winter weather expert at the Weather Channel after a 32-year career at the National Weather Service office in Buffalo.