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 also a moderately hot month, with average temperature fluctuating between 51.1°F (10.6°C) and 78.8°F (26°C).

Temperature

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

Humidity

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

Rainfall

In Boise, it is raining for 3.7 days, with typically 0.6" (14.7mm) of accumulated precipitation. In Boise, during the entire year, the rain falls for 87.6 days and collects up to 11.7" (297.9mm) of precipitation.

Snowfall

In Boise snow does not fall in May through September.

Daylight

In Boise, the average length of the day is 12.5h.

Sunshine

The average sunshine in Boise is 10.1h.

UV index

The average daily maximum UV index is 6. A UV Index estimate of 6 to 7 represents a high health hazard from unprotected exposure to the Sun's UV rays for average individuals.
Note: In September, the average maximum UV index of 6 translate into the following recommendations:
Take precautions against overexposure. Protection against sun damage is needed. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.

What is the temperature in September in Boise?

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

How much does it rain in Boise in September?

In Boise, Idaho, in September, during 3.7 rainfall days, 0.6" (14.7mm) of precipitation is typically accumulated.

Does it snow in Boise in September?

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

When it does not snow in Boise?

May through September are months without snowfall.

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

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

How long on average sun shines in September in Boise?

The average sunshine in September in Boise is 10.1h.

How high is the UV index in September in Boise?

The average daily maximum UV index in September in Boise, Idaho, is 6. A UV Index reading of 6 to 7 represents a high health threat from the exposure to the Sun's UV rays.
Average temperature in September - Boise, ID
  • Average high temperature in September: 78.8°F

The warmest month (with the highest average high temperature) is July (91.2°F).
The month with the lowest average high temperature is December (37.5°F).

  • Average low temperature in September: 51°F

The month with the highest average low temperature is July (60.4°F).
The coldest month (with the lowest average low temperature) is December (24°F).

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: 0.6"

The wettest month (with the highest rainfall) is December (1.6").
The driest month (with the lowest rainfall) is August (0.2").

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: 0"

The month with the highest snowfall is December (7").
Months with the lowest snowfall are May, June, July, August and September (0").

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).