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

September in Yellowstone National Park brings a decrease in the average high-temperature, falling from August's pleasant 71.4°F (21.9°C) to an enjoyable 61.5°F (16.4°C). Yellowstone National Park anticipates a considerable drop in temperature at night in September, with an average low 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

January through June, September through December are months with snowfall. September is the first month it typically snows. 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 in Yellowstone National Park is 12h and 30min.
On the first day of the month, sunrise is at 6:46 am and sunset at 7:58 pm. On the last day of September, sunrise is at 7:19 am and sunset at 7:04 pm MDT.

Sunshine

In September, the average sunshine is 8h.

UV index

In Yellowstone National Park, the average daily maximum UV index in September is 6. A UV Index estimate of 6 to 7 represents a high health risk from unprotected exposure to Sun's UV rays for average individuals.
Note: In September, a regular UV index of 6 translates into these guidelines:
Persist with precautions and heed sun safety advice. Prevention of sunburn is compulsory. The Sun emits the most powerful UV radiation between 10 a.m. and 4 p.m. Try to avoid direct sunlight during this period. Counter UV radiation's ill effects with clothing designed for sun safety and UV-resistant eyewear. Take heed! The reflection of snow can intensify the Sun's UV radiation nearly double.