If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Guernsey: The hottest months are usually July and August, with an average temperature of 21°C, while the coldest months are February and January, with an average of -1°C. The snowiest months in Guernsey are January, November, February and December, with each month seeing an average of 13 cm of snowfall.