Boissy-l'Aillerie has an oceanic climate (Köppen climate classificationCfb). The average annual temperature in Boissy-l'Aillerie is 11.2 °C (52.2 °F). The average annual rainfall is 635.8 mm (25.03 in) with December as the wettest month. The temperatures are highest on average in July, at around 18.9 °C (66.0 °F), and lowest in January, at around 4.3 °C (39.7 °F). The highest temperature ever recorded in Boissy-l'Aillerie was 41.6 °C (106.9 °F) on 25 July 2019; the coldest temperature ever recorded was −17.8 °C (0.0 °F) on 17 January 1985.
Climate data for Boissy-l'Aillerie (Pontoise - Aero, altitude 87m, 1991–2020 normals, extremes 1946–present)