Denver features a semi-arid climate (Köppen climate classification "BSk") with very low humidity and around 3,100 hours of sunshine per year. The weather of the city and surrounding area is influenced by the proximity of the Rocky Mountains to the west. The climate, while generally mild compared to the mountains to the west and the plains further east, can be moderately unpredictable. Measurable amounts of snow have fallen in Denver as late as Memorial Day and as early as Labor Day. Most recently, Denver received an inch of snow on September 8, 2020, making this the second earliest measurable snowfall on record.