The climate is mild and dry all throughout the year. Here is a rough Guide to the weather and the best time to visit Santorini:
Summer: During the summer temperatures are never too harsh. The evenings can be chilly so do carry some jackets and scarves. Summer is the peak tourist Season in Santorini and it starts in April and ends in October. Best months to visit are between July and September when the sun shines brightly and beautifully.
Winter: From October to March is the winter. It can be very cold during winter so you are advised not to travel during this time. Most attractions will be deserted and museums closed.