This route crosses from the humid Basque coast through Álava to the drier plateau toward Burgos, so conditions shift noticeably with elevation and exposure. April, May, and September align with milder temperatures and longer days between lingering spring showers and the hotter, drier inland summer, particularly across Castile and León. Expect regular rainfall near the coast year‑round, variable skies in transitional months, hotter afternoons inland in midsummer, and colder, occasionally wintry spells in midwinter, including freezing rain or snowfall at times.