Seasons, temperature, what to wear in Hokkaido

Situated at the northernmost point of Japan, Hokkaido's colorful seasons are very distinct from each other. March to May is spring; June to August is summer; September to November is autumn; December to February is winter. Using the central city of Sapporo as a reference, the average temperature is 12.4℃ in spring (May), 22.3℃ in summer (August), 4.9℃ in autumn (November) and 3.4℃ below 0 in winter (February). There is thus a lot of variation in temperature. There are days in spring and summer when a T-shirt is fine, but the temperature drops in the evening and morning so you should have something with long sleeves handy. Don't forget to prepare for the cold in autumn and winter. For the deep snow and cold of winter, you will need not only pullovers and jackets but scarves and gloves and warm shoes. The weather also depends on which city you visit, so make sure you check the weather information beforehand and choose appropriate clothes.
Average temperature in major cities of Hokkaido and all over Japan

Season   Seasonal topics Average maximum temperature (Sapporo) Average minimum temperature (Sapporo) Clothing
Spring (March - May) March March still has its fair share of cold northwesterly winds and chilly temperatures, an excellent season to enjoy seafood from the northern seas, like horsehair crab and scallops. 3.5 -3.5 There is a big temperature difference between the morning and evening. Nights can still be wintry, so it's best to have a jacket, gloves and scarf ready just in case.
April April, there is a breath of spring in the air as the land comes to life. The winds are still chilly, but the latter half of the month will see cherryblossom buds begin to appear. 11.1 2.7 Still chilly despite it being spring, so a light jacket is required. Scarves and stoles to keep your neckline warm are also recommended.
May With comfortable temperatures during the day, this is also the best season to see cherryblossoms and azaleas. 17 7.8 You will still experience cold winds on many days, so have a warm top handy, like a blouson.
Summer (June - August) June It is the rainy season in other parts of the country, but since Hokkaido does not have a rainy season, there are more and more sunny days. There are also plenty of events to welcome the early summer. 21.1 12.4 There are some days which you can spend in a T-shirt, but there are still periods which can be cold depending on the weather, so do have a light top like a cardigan or parka ready.
July There are not many rainy days in July, just enjoyment of the refreshing summer weather. The best season for travel with lots of summer festivals and other events. 25 17.1 Enjoy the towns in short sleeves, but have a light parka etc. with you when you travel to the mountains or lakes.
August Mid-summer is great for sports in the great outdoors, taking in the mountains and forests. The best season to see summer flowers like sunflowers is early in the month. 26.1 18.5 Short sleeves are enough in the middle of summer. There can be cold days in late August in Hokkaido, so have a light top ready, like a parka.
Autumn (September - November) September Rainiest part of the year, with some hints of autumn. Prime season for beautiful sunsets. 22 13.6 There are sunny, warm days, but it can get cold very quickly. Dress in short sleeves, but have a light jacket handy.
October October sees the beautiful reddening of the leaves and a sharp drop in temperature. Various gourmet events are held around the prefecture. 15.8 6.9 The mornings and evenings get chillier in October, so make sure you have a light jacket. Dress in long-sleeves, and have something to wear over the top.
November The cold deepens in November as more and more days take a wintry turn. And with the cold comes the migration of wild birds. 8.1 0.9 A coat is a must in November as the first snows arrive. Late November can see days where a heavy coat is appropriate.
Winter (December - February) December It begins to snow properly, and the wintry town of Sapporo is lit with beautiful seasonal illumination. 2.1 -4.4 As the snows create a wintry cityscape, a heavy coat is essential by late December. Gloves and slip resistant winter boots are also required.
January The maximum temperature drops below 0 in January, and the snow is deepest. In the Okhotsk Sea to the east, a seasonal highlight is the arrival of ice floes. -0.9 -7.7 Have mid-winter clothing like down jackets ready for January, and don't let the cold seep in. Have hooded down jackets, wooly hats and scarves ready for snowy days.
February The average temperature is still below zero in February. There are plenty of events to enjoy the winter cold, like the popular Sapporo Snow Festival. -0.3 -7.2 Very cold days continue in February, so you should be just as prepared as you were for January. Warm inner wear and heating pads help deal with the cold.