Bogotá has an oceanic climate (Köppen ''Cfb'') bordering on a warm-summer Mediterranean climate (''Csb''). The average temperature is , varying from  on sunny days to  on rainy days. Dry and rainy seasons alternate throughout the year. The driest months are December, January, July and August. The warmest month is March, bringing a maximum of . The coolest nights occur in January, with an average of  in the city; fog is very usual in early morning, 220 days per year, whilst clear sky sunny full days are quite unusual.