Being in the subtropical zone, Shanghai weather varies strongly over the course of the year.
Summers tends to be very hot, with the back ground noise of cicadas (see post Singing trees and Shanghai heat), the damp atmosphere feeling more like tropical Saigon. On the opposite, winters are cold and damp (See post freezing Shanghai). While snow is rare (see post snow in Shanghai), the humidity makes living in the city really miserable for a few days. Mid-season between those Scylla and Charybdis are really nice, and best to visit Shanghai either in spring, or in Autumn.
Shanghai sub tropical sun light is very strong and a few sunny hours tend the change the city mood really fast. This is why most houses face South, as light coming directly inside the home will brightens up the dampest winter day. In the rare days of winter sunshine, lanes fill up with hanging clothes and bedding, the sun light being most effective to chase away bugs and humidity of the old houses.
Best days for me are also those blue sky days in winter, even better late winter or early spring. Winter time is a particularly great time to look at old architecture in the former concessions. While plane trees leafs provide a nice shadow in the summer, they tend to cover up low rise buildings from the 1920s and 30s. Winter see the leafs disappear and the buildings appearing clearly. It’s a great time to walk around, look at the buildings and take photographs. With the spring a few days away, buds will soon open before becoming leafs. They will recreate the charming green vault overlooking the streets, but will also cover Old Shanghai low rise buildings. With a few days to enjoy it, every day of blue sky is an opportunity to discover more about Old Shanghai, so just go out and look around before it’s too late… for this year.