The proximity to the Bay of Biscay gives Bilbao an oceanic climate (Cfb), with precipitation occurring throughout the year, without a well-defined dry summer season. This precipitation is abundant, and given the latitude and atmospheric dynamics, rainy days represent 45% and cloudy days 40% of the annual total. The rainiest season is between October and April, November being the wettest. Snow is not frequent in the city, while it is possible to see snow on the top of the surrounding mountains. Sleet is more frequent, about 10 days per year, mainly in the winter months.
Said proximity to the ocean also makes that the two most defined seasons (summer and winter) remain mild, with low intensity thermal oscillations. Average maximum temperatures varies between 25 °C(77.0 °F) and 26 °C (78.8 °F) in the summer months, while the average minimum in winter is between 6 °C (42.8 °F) and 7 °C(44.6 °F).
Extreme record observations in Bilbao are 42.2 °C (108.0 °F) maximum (on 13 August 2003) and −8.6 °C (16.5 °F) minimum (on 3 February 1963). The maximum precipitation in a day was 225.6 mm (9 in) in 26 August 1983 when severe flooding was originated by the Nervión river
