September in Denver is usually a sunny and very pleasant month.
In fact, the highest monthly percentage of sunshine of the year can be found during September. The weather pattern also begins to change this month, with both daytime and nighttime temperatures becoming much cooler by the end of the month.
Although autumn begins Sept. 23, summery weather and even winterlike weather are not completely uncommon.
High temperatures above 90 degrees can still occur, even into late September. In 2010, record high temperatures above 90 degrees occurred four times, all of which happened over the past two weeks of the month. In total, there were 25 days last September in which the high temperature was at least 80 degrees, including eight days in which the high was at least 90.
Snowfall in Denver during September is fairly rare but not unheard of. The last time measurable snowfall fell in September was in 2000, when 0.2 inches fell. The earliest snowfall on record in Denver occurred Sept. 4, 1961, when 4 inches fell. Also of note, 9 inches of snow fell Sept. 29, 1985; this was accompanied by a daytime high of only 29 degrees.
