Boise
Idaho, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Boise, ID

The golden fall season in Boise, Idaho, with the tall city buildings
The golden fall season in Boise, Idaho, with the tall city buildings
September, the first month of the autumn, in Boise, is still a warm month, with average temperature varying between 78.8°F (26°C) and 51.1°F (10.6°C).

Temperature

In September, the average high-temperature decreases, from a tropical 89.8°F (32.1°C) in August, to a warm 78.8°F (26°C). The average low-temperature, in September, is 51.1°F (10.6°C).

Humidity

The average relative humidity in Boise is 45.1%.

Rainfall

In Boise, in September, during 3.7 rainfall days, 0.6" (14.7mm) of precipitation is typically accumulated. Throughout the year, in Boise, there are 87.6 rainfall days, and 11.7" (297.9mm) of precipitation is accumulated.

Snowfall

In Boise, it doesn't snow. In October, it regularly snows. Throughout the year, 19.2" (487.5mm) of snow is accumulated.

Daylight

The average length of the day in Boise is 12.5h.

Sunshine

The average sunshine in Boise, Idaho, is 10.1h.

UV index

The average daily maximum UV index in Boise is 6. A UV Index reading of 6 to 7 represents a high threat to health from unsafe exposure to the UV radiation for the average person.
Note: The daily maximum UV index of 6 in September interpret into the following advice:
Take precautions against overexposure. Fair-skinned people may get burned in less than 20 minutes. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. A wide-brim hat offers excellent sun protection for eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun.

What is the temperature in September in Boise?

In Boise, in September, the average high-temperature is 78.8°F (26°C), and the average low-temperature is 51.1°F (10.6°C).

What is the average humidity in September in Boise?

In Boise, Idaho, the average relative humidity in September is 45.1%.

How many days does it rain in September in Boise?

In Boise, in September, it is raining for 3.7 days, with typically 0.6" (14.7mm) of accumulated precipitation.

Does it snow in Boise in September?

In Boise, Idaho, in September, it doesn't snow. In October, it regularly snows.

What is the average length of the day in September in Boise?

The average length of the day in September in Boise is 12.5h.

How long on average sun shines in September in Boise?

The average sunshine in September in Boise, Idaho, is 10.1h.

What is the UV index intensity in September in Boise?

The average daily maximum UV index in September is 6. A UV Index reading of 6 to 7 represents a high health threat from the exposure to the Sun's UV radiation.
Average temperature in September - Boise, ID
  • Average high temperature in September: 26°C

The warmest month (with the highest average high temperature) is July (32.9°C).
The month with the lowest average high temperature is December (3.1°C).

  • Average low temperature in September: 10.6°C

The month with the highest average low temperature is July (15.8°C).
The coldest month (with the lowest average low temperature) is December (-4.4°C).

Average humidity in September - Boise, ID
  • Average humidity in September: 45.1%

The month with the highest relative humidity is January (75%).
The month with the lowest relative humidity is July (36.1%).

Average rainfall in September - Boise, ID
  • Average rainfall in September: 14.7mm

The wettest month (with the highest rainfall) is December (39.4mm).
The driest month (with the lowest rainfall) is August (6.1mm).

Average rainfall days in September - Boise, ID
  • Average rainfall days in September: 3.7 days

The month with the highest number of rainy days is December (11.8 days).
The month with the lowest number of rainy days is August (2.4 days).

Average snowfall in September - Boise, ID
  • Average snowfall in September: 0mm

The month with the highest snowfall is December (177.8mm).
Months with the lowest snowfall are May, June, July, August and September (0mm).

Average snowfall days in September - Boise, ID
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is December (6 days).
Months with the lowest number of snowfall days are May, June, July, August and September (0 days).

Average daylight in September / Average sunshine in September - Boise, ID
  • Average daylight in September: 12.5h

The month with the longest days is June (Average daylight: 15.4h).
The month with shortest days is December (Average daylight: 9h).

  • Average sunshine in September: 10.1h

The month with most sunshine is July (Average sunshine: 12.9h).
The month with least sunshine is December (Average sunshine: 3.4h).

Average UV index in September - Boise, ID
  • Average UV index in September: 6

Months with the highest UV index are June and July (UV index 9).
Months with the lowest UV index are January and December (UV index 1).