Rome and its metropolitan area has a Mediterranean climate (Köppen climate classification: Csa),^[1] with mild winters and warm to hot summers. According to Troll-Paffen climate classification, Rome has a warm-temperate subtropical climate (Warmgemäßigt-subtropisches Zonenklima).^[2] According to Siegmund/Frankenberg climate classification, Rome has a subtropical climate.^[3]

Rome is more southerly than most cities in Europe, and the duration of daylight throughout the year is more similar to Chicago or New York City (all three at approximately 40°N) than Berlin (~52°N) or Paris (48°N). Days in winter are not as short as in northern Europe, and the average duration of daylight in December, January and February is 10 hours^[4] (for comparison: London^[5] or Moscow^[6] or Warsaw^[7] – about 8 hours).

Sunshine duration is about 2,500-2,700 hours per year, from 147 – average 4.7 hours of sunshine per day in December to 338 – average 10.9 hours of sunshine per day in July.^[8] With the exception of Madrid,^[9] Lisbon^[10] and Athens,^[11] Rome has the highest UV index between European capitals (only in the continent) and values close to that of Chicago at 41.9 °N as ultraviolet radiation is less interfered with by other geographic variables, but with a moderate annual average with index equal to 5, which allows direct exposure to the sun at some times of the year. Values range from 1 (December) to 9 (July).^[12]

• Climate of Ancient Rome