The most common traditional definition uses the position of the Earth relative to the Sun. Autumn begins with the autumnal equinox (around September 22–23) and ends with the winter solstice (around December 21–22). Under this system:

The question β€œWhat month is autumn in the USA?” appears straightforward; however, the answer varies significantly depending on whether one uses astronomical, meteorological, or cultural definitions. While laypersons often point to September, October, and November, different scientific and practical systems offer contrasting boundaries. This paper clarifies the three primary methods used to define autumn in the United States.

Because the USA is a massive country spanning multiple climate zones, the "autumn feel" varies greatly by region. Here is what happens during the core autumn months:

To answer the question directly:

Defined by the Earth's orbit, it officially begins on the autumnal equinox (usually September 22 or 23) and ends on the winter solstice (usually December 21 or 22). Seasonal Highlights When does Autumn/Fall start for you? : r/AskAnAmerican

Defined by temperature cycles and the Gregorian calendar, this season runs from September 1 to November 30 .

Here is a breakdown of what months constitute autumn in the USA and what you can expect during each one.

It is important to remember that the USA covers a vast area.

If you are planning a trip to the United States or simply trying to understand the seasonal calendar, you may be wondering: