Typically, Philadelphia experiences a transition from summer to autumn during September. This period is characterized by gradually decreasing temperatures, lower humidity, and fewer daylight hours. Average high temperatures fall from the low 80s Fahrenheit (around 28 degrees Celsius) at the beginning of the month to the low 70s Fahrenheit (low 20s Celsius) by the end. Overnight lows follow a similar trend, moving from the mid-60s Fahrenheit (around 18 degrees Celsius) to the mid-50s Fahrenheit (around 13 degrees Celsius). Rainfall amounts remain relatively consistent with other months, averaging around 3-4 inches.
Understanding these typical conditions is valuable for planning a variety of activities, from outdoor events and tourism to gardening and home maintenance. Historically, this shift in climate signaled the end of the summer growing season and the beginning of harvest preparations. This seasonal change also influenced local commerce and social activities, with festivals and markets adapting to the cooler weather. Preparing for the shift from summer heat to autumnal coolness contributes to comfort and safety.