Sana'a sits at 2,200 metres, and the altitude moderates the climate dramatically: days are warm and dry year-round, nights are cool, and the city escapes the brutal heat that flattens the Yemeni lowlands in summer. The result is one of the most agreeable climates in the Arab world.
October to March is the dry and clear season — sunny days, cool nights (occasionally down to near freezing in January), and the best light for photographing the old city. April and May bring brief afternoon thunderstorms; July and August are warmer and rainier, with the short summer monsoon that turns the surrounding hills green.
Note: travel to Yemen is currently not safe and has been since 2015. This guidance applies for when conditions allow visits again.