Climate Montagnieu has an
oceanic climate (
Köppen climate classification Cfb). The average annual temperature in Montagnieu is . The average annual rainfall is with November as the wettest month. The temperatures are highest on average in August, at around , and lowest in January, at around . The highest temperature ever recorded in Montagnieu was on 13 August 2003; the coldest temperature ever recorded was on 7 February 2012. {{Weather box ==Population==