December is the start of winter across Japan, but it tends to be a milder month than January or February. Wherever you go, you'll need a good jacket, but in many places the temperatures aren't cold enough to avoid outdoor sightseeing. Temperatures tend to be warmer earlier in the month than later.
The major cities of Honshu and Kyushu (Tokyo, Osaka, Kyoto, Fukuoka) experience average December highs of around 54° F (12° C), and lows of 41° F (5° C). The Japan Alps area of Honshu is significantly colder, with the city of Takayama experiencing highs of 43° F (6° C) and lows of 28° F (-2° C). Hokkaido is much colder, with Sapporo experiencing highs of 36° F (2° C) and lows of 25° F (-4° C). In contrast, the sub-tropical and tropical islands of Okinawa are pleasantly warm but not hot, with average highs in Naha of 70° F (20° C), and lows of 61° F (16° C).
Expect snow in Hokkaido and northern parts of Honshu (Tohoku), but elsewhere there is little rain and high sunshine hours. Tokyo and Osaka, in particular, are very sunny in December, making up for the cooler temperatures.
Crowds and Costs
Although winter is low season in much of Japan, it's also the start of the ski season in higher altitude or latitude places. However, in many mountainous places the snowfall in December is inconsistent, and ski season tends to begin in January. But if you're traveling to Japan in December and really want to ski, check out local and up-to-date conditions to see if the season is starting slightly earlier anywhere.
Domestic travel increases towards the end of the month. Many Japanese people take holidays in the lead up to the new year (and straight afterwards), so many places are busier at this time of the month. Book accommodation and domestic travel (such as bullet trains) far in advance if traveling to Japan in late December.
Where to Go
Unless you really want to experience cold temperatures and snow, stick to central and lower Honshu and the islands of Kyushu and Shikoku. With high sunshine hours in Tokyo and Osaka (which is near many other places, such as Kyoto, Kobe, and Nara), December is a good time to hit Japan's main cities. Culturally and naturally beautiful places like Kyoto are especially picturesque in December. In the cities, you can enjoy some outdoor activities such as gardens and parks, and when you start to feel cold you can retreat to a museum, gallery, or restaurant.
The area around Mt. Fuji is a nice place to head in December, as you're likely to get good views of the snow-covered mountain. Plus, there are lots of hot spring baths in the area—some of which even have views of Fuji—which are especially nice to relax in when it's cold out.
If you'd prefer slightly warmer December temperatures, and even the chance to see the last of the autumn leaves earlier in the month, then head to Kyushu. Japan's third-largest island has a great mix of interesting cities (Fukuoka, Nagasaki, Kumamoto), mountains and volcanoes, hot spring resorts, and coastline.
Chat with a local specialist who can help organize your trip.
What to Do
As mentioned above, December is a great time to enjoy a quintessentially Japanese pastime: soaking in an onsen bath. You'll find these all over the country, but specific onsen resort towns can be great destinations because you can find a variety of different baths close together, including indoor baths, baths with views, and baths with interesting natural features (like being set in a cave!)
Most travelers will enjoy general sightseeing in Japan's towns and cities during December because you can mix indoor and outdoor activities depending on how cold it is outside.
Christmas. Although most Japanese don't celebrate Christmas as a religious holiday, and neither is it a day off work, you'll find festive Christmas lights and trees around the country, especially in the big cities. Christmas markets with a European twist (think: mulled wine) also set up in various places, most notably at Roppongi Hills and Hibiya Park in Tokyo and the Akarenga Christmas Markets in Yokohama.
New Year. As well as the typical countdown parties at bars in the big cities, the new year is celebrated at shrines across Japan. Many people line up in cold nighttime temperatures to welcome the new year with a prayer at their local shrine. At bigger shrines, you'll probably find food and drink stalls lining the pathway.
Traveling to Japan in December? Check out these great itineraries
Best of Old and New Japan: Tokyo, Kyoto, & More - 14 Days. The combination of historic and modern beauty makes Japan an ideal vacation destination. On this journey of old world-meets-new world, you will explore the progressive cities and also stroll through pockets of old Japan.
Japan's Culinary Heritage - 11 Days. Eat your way through the Land of the Rising Sun on this immersive culinary tour. Get to know Japanese history and culture through its legendary cuisine.
Classic Highlights of Japan - 14 Days. On this two-week journey to the four corners of Japan's main island, Honshu, you'll have plenty of time to enjoy its unmissable attractions. You'll visit sacred temples and shrines, go bike riding through the countryside, and roam around the capital's most famous neighborhoods.