September weather forecast
Yellowstone National Park, WY

As the onset of autumn begins in Yellowstone National Park, September sees a noteworthy dip in temperature, though it climbs to a still mild 61.6°F (16.4°C). This cooler period facilitates the return of snowfall, albeit only a paltry 1.3" (33mm). The change in weather invokes a rich shift in the park's color palette with reds, oranges, and yellows adorning the landscape. This golden month provides a picturesque setting for photographers and nature enthusiasts alike.

Temperature

The beginning of September marks a decrease in the average high-temperature, transitioning from an agreeable 71.4°F (21.9°C) in August to an enjoyable 61.5°F (16.4°C). The September nights bear witness to a significant drop from the daytime highs, settling at an average temperature of 31.8°F (-0.1°C).

Rainfall

In Yellowstone National Park, in September, it is raining for 9.7 days, with typically 1.46" (37mm) of accumulated precipitation. In Yellowstone National Park, during the entire year, the rain falls for 151 days and collects up to 20.91" (531mm) of precipitation.

Snowfall

Months with snowfall are January through June, September through December. September is the first month it typically snows in Yellowstone National Park. Throughout September, in the average 1.1 snowfall days, it receives 1.3" (33mm) of snow. In Yellowstone National Park, during the entire year, snow falls for 91.4 days and aggregates up to 193.7" (4920mm) of snow.

Daylight

In September, the average length of the day is 12h and 30min.
On the first day of September, sunrise is at 6:46 am and sunset at 7:58 pm. On the last day of the month, sunrise is at 7:19 am and sunset at 7:04 pm MDT.

Sunshine

In Yellowstone National Park, the average sunshine in September is 8h.

UV index

In September, the average daily maximum UV index is 6. A UV Index value of 6 to 7 symbolizes a high health vulnerability from unsafe exposure to UV radiation for the average person.
Note: A typical high UV index of 6 in September suggests the following recommendations:
Deter overexposure. Protecting against the sun's effects is essential. The Sun's UV radiation is most intense from 10 a.m. to 4 p.m. Try to avoid direct sun exposure during these hours. Wearing sunglasses with both UVA and UVB protection effectively reduces sun-induced eye damage. Note this! The Sun's UV radiation can nearly be doubled by the reflection off snow.