[GoNative]

I find the climate in Japan to be fascinating but then I've always found weather and climate fascinating (that's why I majored in meteorology for my science degree).
Japan's climate really is quite unique. Being an island situated off the east of the huge Asian continent with a relatively mild body of water in between (The Sea of Japan) Japan has almost more of a continental than maritime climate even though it's an island.
There is huge variation in the climate from the southern islands around Okinawa situated in the sub tropics to the the cool temperate zone up in Hokkaido.
In the summer months much of Japan is affected by the East Asian Monsoon. This usually takes the form of a quasi-stationary front that gradually moves up through Honshu during June but rarely makes it right up to Hokkaido and if it does generally only briefly. In it's wake hot and very humid air coming up out of the South China Sea predominates throughout Honshu. From around September typhoons start making their way up towards Japan and can bring huge amounts of rain. Again these rarely make it all the way up to Hokkaido which on the whole manages to remain reasonably mild and definitely not so humid throughout the summer.
By October the quasi-stationary front has started moving back down bringing relief from the heat and humidity and by mid October frosts are becoming common up in Hokkaido and the peaks of the mountains are already dusted in snow.
By October Siberia is mostly covered in snow and already averaging temperatures well below freezing. Normally a reasonably strong stationary high pressure system starts to dominate over Eastern Siberia and low pressure systems start developing in the Sea of Okhotsk and Northern Pacific. When these combine cold air flows out of Siberia across the Sea of Japan and over Japan. First snowfalls to sea level start occurring from late October to early November in Hokkaido and by the end of Nov into early Dec regular cold outbreaks start bringing snow to lower levels right along the western seaboard of Japan. Because the cold air crosses the reasonably mild waters of the Sea of Japan it picks up a lot of moisture in what's know as the 'sea effect' which brings some of the heaviest snowfalls in the world to the western slopes of the mountains in Honshu and Hokkaido. It is a similar effect to the 'lake effect' snows experienced on the Eastern side of the Great Lakes in the US but a much more pronounced effect as it's a much larger body of water. Winters are long, cold and snowy up in Hokkaido and quite mild and short down in Kyushu.
The Spring and Autumn seasons are often fairly brief between the two major seasons Summer and Winter but they often have some of the best weather of the year.
Of course there's a whole lot more to it all. The other major factors that effect the climate here are two major ocean currents, the warm Kuroshio and the cold Oyashio. The paths these currents take can greatly effect the paths of major weather systems from year to year. Lots of other long term more global climate factors that affect the weather and climate here of course like El Nino, Arctic Oscillation, Pacific Decadal Oscillation, etc, etc.

Overall the climate here is pretty amazing. I'm still amazed at how hot and humid it can get in summer but by winter be snowing to sea level. Huge variations from North to South and from season to season. The climate has had a pretty big effect on Japanese culture and many of the biggest festivals throughout the year celebrate the changing of the seasons.