Istanbul is characterized as having a Mediterranean climate, according to the updated Köppen-Geiger classification system. However, due to its vast size, diverse topography, and maritime location, Istanbul exhibits microclimates. Northern parts of the city express characteristics of anoceanic climate because of humidity from the Black Sea and the relatively high concentration of vegetation. The climate in the populated areas of the city in the south is warmer and less affected by humidity.
Summer weather in Istanbul is warm, with high temperatures in July and August averaging 28 °C(82 °F). Extreme heat, however, is uncommon, as temperatures rise above 32 °C (90 °F) on only five days per year on average. Rainfall is also uncommon during the summer, with only four or five rainy days per month. Winters are cold, wet, and often snowy, with the temperature in January and February averaging 4 °C(39 °F). Snowfalls tend to be heavy, but snowcover and temperatures below freezing rarely last more than a few days. Spring and autumn are mild, but often wet and unpredictable; chilly winds from the northwest and warm gusts from the south—sometimes in the same day—have the tendency to cause fluctuations in temperature.
Istanbul has a persistently high humidity, which can exacerbate the summer heat. Humidity generally reaches eighty percent, particularly during the morning hours, and fog is very common although it usually dissipates by noontime. The city receives fog an average of 228 days each year, with the highest concentration of foggy days being in the winter months. Thunderstorms are uncommon, occurring just 23 days each year, but they occur somewhat frequently in the summer and early autumn months. Istanbul has an annual average of 124 days with significant precipitation, which amounts to 855 millimeters (33.7 in) per year. The highest and lowest temperatures ever recorded in the city are 40.5 °C (105 °F) and −16.1 °C (3 °F), respectively. The
