Map from Google - Asturias

In the autonomous community of Asturias, in the north of Spain, the climate is cool and damp, because of the influence of the Atlantic Ocean. Winters are relatively mild and rainy, while summers are cool and fairly sunny. Atlantic frontal systems can pass all year round, although they grant a relative lull in summer, when, hoewever, thunderstorms can break out in the afternoon or in the evening.
The wind blows frequently, so there are several beaches frequented by surfers.
Also fog is common: it can show up all year round, when there is no wind, and even on summer nights, especially along the coast and in the valleys.
In winter, cold air masses from the northern Atlantic Ocean and continental Europe can lead to cold and windy periods, but on the coast very cold days are rare (the cold records are a few degrees below freezing). However, even on mild days the wind can increase the feeling of cold. Snow, very rare on the coast, becomes a bit more frequent in inland hilly areas, for example in Oviedo, which is located 340 metres above sea level. In the mountains instead, snowfalls may be abundant.

Oviedo under the Snow

The rains are quite abundant, given that they hover around 1,000 millimetres per year on the coast and hilly areas, and are frequent, especially from October to May, while in summer their frequency diminishes a bit. Because of the abundance and frequency of rain, the landscape is green.
In the interior we find hills, and in the southern part of a mountain range, the Cantabrian Mountains, which separates this cool and moist part of Spain from the arid central plateau (meseta); in particular in the southeast stand the Picos de Europa ("Peaks of Europe"), whose highest peak is Torrecerredo, 2,648 metres high; these mountains receive heavy snowfalls in winter. There are also skilifts. Around a thousand metres of altitude we find the lakes Enol and Ercina (also called Lakes of Covadonga).
In mountainous areas there are parks, such as Parque Natural de las Ubiñas - La Mesa, Parque Natural de Somiedo, and Parque Natural de Redes.
The wind that comes down from the mountains may cause rapid increases in temperature, due to the föhn effect, so that along the coast the temperature may exceed 20 °C in winter, and 30 °C in autumn and spring, while in summer this hot wind is very rare.
On the coast of Asturias, or Green Coast, rugged and characterized by coves and natural caves, there are several beaches and resorts such as Cabo de Peñas, Luarca, Luanco, Aviles, Gijón, Cudillero, Llanes and Ribadesella.
Here are the average temperatures of Gijon, the largest city, located on the coast.
Average temperatures - Gijón
GijónJanFebMarAprMayJunJulAugSepOctNovDec
GijónJFMAMJJASOND
Min (°C)567911141617151286
Max (°C)141415161820232322191614

In Gijón, 955 mm of rain per year fall, with a maximum in autumn and a relative minimum in summer, when however there is no lack of rainy days.
Here is the average precipitation.
Average precipitation - Gijón
GijónJanFebMarAprMayJunJulAugSepOctNovDecYear
GijónJFMAMJJASONDY
Prec. (mm)858075907055456070105125105955
Days12111112117688111313124

In the capital, Oviedo, which as mentioned is located 340 metres above sea level, temperatures are similar to those of Gijón, although they are a bit lower at night and in winter.
Here are the average temperatures.
Average temperatures - Oviedo
OviedoJanFebMarAprMayJunJulAugSepOctNovDec
OviedoJFMAMJJASOND
Min (°C)556710121515131075
Max (°C)121315161821232322191512

In Oviedo 1,005 mm of rain per year fall; summer is the least rainy season, but it rains 8/9 days per month also from June to August (or September, when the weather is somewhat similar).
Here is the average precipitation.
Average precipitation - Oviedo
OviedoJanFebMarAprMayJunJulAugSepOctNovDecYear
OviedoJFMAMJJASONDY
Prec. (mm)85856010585604560701051201051005
Days11111113139888121312128

The amount of sunshine in Asturias is never very good: in July and August there are 5.5/6 hours of sunshine per day in cities like Avilés, Oviedo and Gijón; in other seasons, and especially in late autumn and winter, it is even worse, and the sky is often cloudy.

Torimbia beach, Llanes

The sea along the coast of Asturias is a bit cold even in summer, since it reaches 19 degrees in July and 20 °C in August, as you can see in the following table, on the sea temperature at Gijon.
Sea temperature - Gijón
GijónJanFebMarAprMayJunJulAugSepOctNovDec
GijónJFMAMJJASOND
Sea (°C)131313131417192019181614

When to go

The best period to visit Asturias is the summer, from June to August or the first half of September, being the driest and sunniest. July and August are the warmest and least rainy months. Even in midsummer, we must take into account some rain, and some nights a little cool on the coast, and a bit cold in inland areas.
In summer, in good weather you can take a break at the sea and sunbathe, with an air temperature often pleasant and a cool breeze from the ocean, although as I said the sea is cold for swimming.