Bilbao, 16m above sea level on the Costa Verde Atlantic coast with what is described as a humid maritime climate. The warming effect of the sea and predominant westerly to north westerly winds result in winter temperatures significantly higher than central spain but not as high as the mediteranean coast. Winter winds from the southeast, south or southwest can bring colder air from the mountains (Pyrenees 200Km to the south east and the Picos de Europea 150Km to the south west)or central spain.
Summer temperatures are also likely to be around 5 deg C below Mediterranean coastal temperatures with a higher chance of rain. Temperatures at this time of year are tempered by the predominant winds from the sea, although southerly or south westerly winds can bring warmer air from central spain.
Daily average temperatures for Bilbao
Source: World Climate