Climate Change Chart of St. Helier, Jersey

Overview of climate changes

Temperature changes

Averaged across calendar months, monthly mean temperature shows a difference of +1.07 °C between the reference periods; this is an unweighted comparison of monthly means, not a day-weighted annual average or a measure of daytime maximum temperatures. The largest monthly increase was in January, with a difference of +2.56 °C. By contrast, April had the largest monthly decrease, a difference of -0.04 °C.

Changes in rainfall

Mean daily rainfall, averaged across calendar months, had a difference of +0.72 mm/day; this summarizes the unweighted monthly means, rather than day-weighted annual rainfall or monthly totals. The largest monthly increase was in December, where mean daily rainfall had a difference of +1.43 mm/day. The largest monthly decrease came in April, with a difference of -0.30 mm/day.

Changes in sunshine duration

Averaged across calendar months, mean daily sunshine duration had a difference of -0.34 hours/day. This is an unweighted comparison of monthly means, not a day-weighted annual average. The largest monthly decrease was in June, with a difference of -0.90 hours/day. The largest increase was smaller in scale: in February, the difference was +0.23 hours/day.

Changes in snowfall

Mean daily snowfall averaged across calendar months had a difference of -0.10 mm/day. This unweighted comparison of monthly means does not imply the same difference in every month, and the rounded summary should not be read as evidence that snowfall was absent. Monthly differences varied in direction: the largest decrease was in January, with a difference of -1.13 mm/day, while the largest increase was in March, with a difference of +0.78 mm/day. These are mean daily amounts, not monthly snowfall totals.