Japan's Epic Snows - December 14-17, 2020

  

Above, Reuters reported 1,000 vehicles stuck on snowbound highways in Japan after a major winter storm dumped as much as 85 inches of snow in some locations.

While the northeastern U.S. was getting pummeled by a major Nor’easter last week, halfway around the world, at about the same latitude, residents in parts of Japan were getting their own epic snowstorm.  Over the course of 3 days Fujiwara set an all-time snowfall record with 219 cm. or 86 inches of snow.  BBC News wrote that 1,000 drivers were stranded in their vehicles during and immediately after the storm.  

For some, this news may come as a surprise, but snow-savvy weather geeks as well as skiers know Japan as one of the snowiest places on earth.  The reason as the old business adage goes is “location, location, location”.  Japan is made up of many islands, its two largest are Honshu and Hokkaido.  The nation is situated in the western Pacific Ocean, separated from the Asian continent by 300-500 miles across the Sea of Japan.  There are several mountain ranges that stretch down the spine of these main  islands, with several peaks exceeding 10,000 ft.

So, what does this location have to do with heavy snow? Below is an image from the NASA polar orbiter satellite showing hundreds of cloud streamers forming on northwest winds, a little downwind of the Asian continent, moving across the Sea of Japan and impacting the western Coast and well inland across Japan.  As is often the case with weather extremes, several ingredients usually come together in the right place at the right time to maximize their effects.  In Japan’s case those ingredients are very cold air over Siberia, transiting the relatively warm Sea of Japan where they pick up heat and moisture, then those winds hit the mountains of Japan perpendicularly, maximizing lift to “squeeze” out moisture in the form of snow. This type of snow event is often referred to as “ocean-effect” or “sea-effect” snow. 

To illustarte just how much the arctic air is wamred as it crosses the Sea of Japan,  I have added the prevailing wind direction along with the temperature upwind of the Sea of Japan at Vladivostok, and the temperature downwind at Wajima for December 16th.  Look at how much the air has heated as it crossed the warm waters of the Sea of Japan, 19.8 degrees Celsius or 35.8 degrees Fahrenheit!

In fact, not only does the surface temperature warm, but the entire column of air warms and moistens considerably through the mid-levels of the atmosphere, where clouds and snow develop, as it crosses the sea. Below are the atmospheric soundings taken at both Vladivostok and Wajima on December 16^th at 00z.  The soundings show two lines, temperature on the right and dewpoint on the left. The x-axis denotes temperature and the y-axis shows altitude in millibars (mb.) of pressure.  For those not familiar with millibars, the 700mb level is approximately 10,000 ft. in altitude and 500m is about 18,000 ft.

Notice at Vladivostok the air is very cold, quite dry and there is a very strong temperature inversion that “caps” the shallow layer of arctic air at a low 1382 m.  (~4500 ft.).  You can't make clouds that produce snow with such a dry and shallow layer of cold air.  Hence the clear skies on the satellite image along the Russian Coast. However, by the time the air has crossed the 400-500 mile distance over the Sea of Japan, at Wajima, the column of air has undergone extensive modification through the mid-levels of the atmosphere as there is a flux, or flow, of heat and moisture that rises from those warm waters into the overlying column of cold air.  As a result, there is a significant decrease in temperature with height, referred to as the lapse rate, and that allows air parcels to stay buoyant and rise rapidly until they get to the temperature inversion.  In fact, the “capping” temperature inversion at Wajima had risen to nearly 4,500 m. (~15,000 ft) and the amount of precipitable water in the column of air has risen from 1.8 mm. at Vladivostok to a whopping 8.4 mm. at Wajima (Precipitable water is the depth of water in a column of the atmosphere, if all the water in that column were precipitated as rain).  Put this all together and by the time those air parcels get across the Sea of Japan, they have produced clouds that grow up through 15,000 ft. and higher, dumping very heavy snowfall. The little cumulonimbus cloud on the Wajima sounding reflects that deep layer of cold, moist air with a steep lape rate, perfect for growing snow clouds. 

The snowfall across the western shore and into the mountains of Japan continued unabated for a 4-day stretch as the large-scale weather pattern persisted.  Below is a 2-hour radar animation from December 16, 2020 along the northern portion of the island of Honshu in the Tohoku Region.  Notice the parallel bands of snow, aligned with, or longitudinally along, west to northwest winds.  As long as the winds stay out of the same direction, the bands of snow will not move, and one area will get huge amounts of snowfall.  I liken this to stick one end of a firehose into the water and pointing the other end downwind over a particular spot.  As long as I do not move the nozzle (change the wind direction) that area I am pointing at gets "pasted" with snow. 

If this sounds familiar to residents of the Great Lakes Region who experience “lake-effect” snow, it should because the concept is the same. However, everything occurs on a much larger scale in Japan. To begin with, the Sea of Japan covers about 12 times the surface area of the Great Lakes.  The average water temperature of the Great Lakes chills to near the freezing point with significant ice accumulation on most of the lakes during mid-winter.  In contrast, the water temperature of the massive Sea of Japan in February is much warmer, averaging some 8 to 12 degrees Celsius (46 to 54 degrees Fahrenheit) even in February.  That equates toi a tremendous amount of energy to fuel these snowstorms. Finally, the various mountain ranges that stretch along the spine of Honshu and Hokkaido exceed 3,000 m. in some locations.  Downwind of the Great Lakes, the Allegany Plateau and Tug Hill Plateau rise less than 1,000 m. MSL.  The Japanese mountain ranges add significant lift to the already buoyant air, maximizing the production of snowfall.

As a result of those characteristics, some locations in Japan, even at low elevations closer to the west coast, see huge annual snowfall on average. Saporro of Winter Olympics Fame, averages about 250 inches of snow each season. Higher up in elevation, some of the mountain locations exceed 500 inches of snow each year (Japan Meteorological Agency, 1981-2010 Normals).  That amount of snow can lead to some amazing snow depths and one of the most famous snowcover images I have ever seen comes from one of these areas a few years back. Visitors from around the world flock to the Tateyama Kurobe Alpine Route (Source: Uryah, Wikipedia Commons, CC BY-SA 3.0) to see the snow corridor that builds each winter season as a result of a few ingredients coming together at the right time and right place in Japan. 

This phenomenon of Mother Nature is just another amazing example of how interesting the atmosphere can be. I often refer to the term “other-worldly” when I see events like this occur. That is why I am so happy to share my curiosity about the weather with you. Enjoy !

BTW, the latest long-range forecast for Eastern Asia the last week in December shows a massive push of Arctic air coming across Eastern Asia/Siberia and right over those warm waters of the Sea of Japan. Methinks there will be even more snow to add to those already amazing totals.  Here is an animation of the 850 mb. level (about 4500 ft. altitude) temperature departures (blue is colder) from Christmas Eve through New Years Eve.