Plomodiern has an oceanic climate (Köppen climate classificationCfb). The average annual temperature in Plomodiern is 11.9 °C (53.4 °F). The average annual rainfall is 1,117.8 mm (44.01 in) with December as the wettest month. The temperatures are highest on average in July, at around 17.8 °C (64.0 °F), and lowest in February, at around 6.9 °C (44.4 °F). The highest temperature ever recorded in Plomodiern was 36.6 °C (97.9 °F) on 9 August 2003; the coldest temperature ever recorded was −10.3 °C (13.5 °F) on 13 January 1987.
Climate data for Plomodiern (1981–2010 averages, extremes 1982−present)