Summer is hot.The other seasons are cool or cold,but often warmer and sunny in the middle of the day.We have four seasons all very different.I am farther north than Zhejiang but we still have probably very similar climate pattern:four totally distinct seasons / conditions.Our winter is frozen cold.But then the other seasons are similar to yours,in a general way.Summer here is mid June to early September.Or,if unlucky,late June to late August.Humid all the time.Lots of rain.25°C+ to 35°C+,and humidity 70%+,80%+ At night it cools off,except when it's a "heat wave" then it's 30°C+ at night.Many people need air-conditioning or else suffer slowness,irritability; can't sleep well,etc.Dangerous storms late summer,but short duration.Still,people like the summer here because it is so much heat after all the cold:it is almost like a vacation.No school for six weeks.
Fall is dryer and cooler.Everybody is happy again; the hot season is over.In early Fall sometimes it warms up again.Fall is long.At first sunny,then clouds,then overcast all day and rainy.Freezes in December.Huge amounts of sun in January February,reflected on snow ground.Very bright.All frozen.The ground doesn't freeze deep where it's snow-covered; snow is like styrofoam insulation keeping ground at a "warm" cold,so plant roots remain in good condition.But cold enough,so we don't have dangerous snakes,scorpions,insects,etc.Winter stops things cold.
Late winter every day big variations:e.g.8°C mid-day,-12°C overnight (air temperature,not in the ground).Spring conditions swing back and forth,like late winter.Big daily/weekly variations,since the sun is so strong and yet there is still so much remaining cold (and cold air far north that comes back every few days).E.g.15°C mid-day,-5°C overnight.
Now with no snow cover,the limiting factor for plant life is start-stop temperatures; many plants die in late Spring after beginning to grow.It's the opposite in Europe and the Mediterranean where every day is almost the same as the previous day,and seasons are not strongly differentiated.European immigrants get depressed in late Spring since they expect to see green things growing "regularly" but everything gets delayed as temperature starts + stops many times.They are often upset in June because the weather in March April and May was not what they have been conditioned to expect.This happens all the time.They love three of the four seasons.In Spring,they just don't "get it".Weather in most of North America is land-based,not maritime-influenced; probably the same as in China.Here,every few days there can be massive changes,as new air moves in from the continent,either from the north or from the south.So,statistical averages are often meaningless.Average temperature may be low,so we build insulated buildings,but daytime conditions are often warm:you can go outside without wearing a big overcoat in the middle of the day,except mid-Winter.
Often (3-4-5 days) the air mass changes.In North America (as in China) the big water mass is on the east side,big land mass on the west.Pacific mountains and Rocky mountains prevent Pacific air from coming into the interior,so the movement of air westward brings new air in from two different sources:far south (Texas) or far north (Yukon).Switching from hot to cold source.