Istanbul Travel Guide - Weather
Winter dœes not usually kick in until the end of November when temperatures typically drop to about 10°C or less and rainfall increases dramatically; November, December and January are by far the wettest months of the year. During December and January night-time temperatures can fall as low as just a few degrees but rarely dœes the city see below-zero conditions.
By February, temperatures are often warm and rainfall begins to subside. March and April are among the most pleasant times of year to visit, when warm weather is virtually guaranteed but things aren’t too sticky. April sees less than half the rainfall that typically occurs in February, for example, and temperatures that hover around 25°C are the norm.