Bilbao Weather Guide: Climate, Seasons & Sirimiri

Bilbao sits in a lush valley along the Nervión River, flanked by the Cantabrian Mountains and the Bay of Biscay. This positioning creates a temperate oceanic climate (Köppen Cfb) that is significantly greener, wetter, and milder than the arid plains of central Spain. Known for its atmospheric "grey" days and unpredictable shifts, the weather here is a defining element of Basque identity.

The "Sirimiri" and Regional Phenomena

To understand Bilbao is to understand sirimiri—a fine, persistent, and almost mystical drizzle. Unlike heavy storm rain, sirimiri is a light mist that can last for hours, coating the city in a damp sheen without ever feeling like a downpour.

Another significant phenomenon is the Foehn effect. When warm southerly winds descend from the Cantabrian Mountains, they compress and heat up rapidly. This can cause the temperature in Bilbao to spike by 10°C (18°F) or more in a matter of hours, occasionally pushing winter afternoon temperatures into the low 20s°C (70s°F).

Seasonal Climate Breakdown

Spring (March – May)

Spring is a period of rapid awakening and high variability. March is often one of the rainiest months, but by May, the city begins to see more consistent sunshine.

• Conditions: Crisp mornings followed by mild afternoons.
• The Feel: The humidity remains high (around 70-75%), so even mild temperatures can feel slightly chilly in the shade or damp after a morning of sirimiri.

Summer (June – August)

Summertime in Bilbao is comfortable rather than scorching. Because of the Atlantic influence, the city avoids the extreme heat found in Madrid or Seville.

• Conditions: Average highs hover around 24°C to 26°C (75°F to 79°F).
• Phenomena: Summer is prone to galernas—sudden, violent coastal storms characterized by a sharp drop in temperature and strong gusts of wind from the northwest.
• The Feel: It feels "fresh." Locals cherish the evening brisa (breeze) that keeps the nights cool and breathable.

Autumn (September – November)

September is arguably the most pleasant month, often acting as a "second summer" with stable, warm days. However, as the season progresses into November, Bilbao enters its wettest period.

• Conditions: Dense morning fogs are common in the valley during October. By November, the Atlantic disturbances bring more frequent rain.
• The Feel: The transition is marked by a shift from the warm, golden light of early autumn to a deeper, moody grey as the humidity rises to near 80%.

Winter (December – February)

Winters are mild and damp. It rarely snows in the city center; when it does, it’s a major event that usually melts by midday.

• Conditions: Daytime highs average around 13°C (55°F). Frost is infrequent and generally limited to the early morning hours.
• The Feel: The "damp cold" is the most notable factor. Because of the 75-80% humidity, a 10°C (50°F) day can feel much sharper than the same temperature in a drier climate.

Microclimates and Variations

Bilbao occupies a "pocket" between the mountains and the sea. This topography creates distinct microclimates:

• The Valley (El Botxo): The city center often traps heat and humidity, making it slightly warmer than the coast.
• The Coast (Getxo/Sopela): Just 15km away at the mouth of the estuary, the wind is much stronger and the air is noticeably saltier and cooler.
• The Mountains (Artxanda/Pagasarri): These peaks frequently disappear into the clouds while the city below remains clear, a visual local signal that rain is imminent.

Local Perspective and Adaptation

Bilbainos have a pragmatic relationship with the weather. Residents often refer to their city affectionately as "Mordor" when the grey skies persist, yet they rarely let the rain stop social life. You will see locals sitting under heated cafe awnings even in mid-winter, nursing a txikito (small glass of wine). The local strategy is to "dress like an onion" (layering), as the temperature can fluctuate wildly depending on whether the wind is blowing from the sea (cool) or the mountains (warm).