Early autumn in Prague is very beautiful. While late autumn can be a bit gray and foggy. This season is best choice to avoid the heat of the summer and take advantage of the changing leaves and open gardens and parks.
This is lovely time to visit when the days are still bright with sunshine. At this time Prague becomes a fairy tale town as beautifully coloured trees with their changing colours often offer spectacular views. The streets are also much less crowded and thus make the autumn a really nice time to visit. November can be a bit grumpy though. Winter can start early in November and the days can be gray seemingly without end. Usually from the beginning of December (sometimes even November) snow is bound to fall and temperatures can be around 0°C.
Consider bringing a jacket, and definitely warm jacket and gloves for November, hat, warm socks, sturdy walking shoes. Don’t expect to wear shorts. You’ll be very lucky to get an Indian summer day!