September weather forecast
Sisters, OR

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Weather in September

As Sisters, Oregon slides into September, summer gently hands over the baton to autumn. A cooler breeze commences, registering a high of 69.8°F (21°C), a marked dip from August's high. September harbors a modestly raised rainfall index, often featuring scattered showers. Humidity levels, however, take a turn upwards. Despite the shortening of daylight hours, cloud cover concentrates, and a shift is noticed dancing amidst the season change.

Temperature

September is marked by a subtle drop in average high-temperatures, transitioning from a moderately hot 78.4°F (25.8°C) in August to a pleasant 69.8°F (21°C). Sisters documents a substantial shift from daytime warmth, recording an average nighttime temperature of 45.1°F (7.3°C) in September.

Humidity

The average relative humidity in September is 61%.

Rainfall

In Sisters, Oregon, during September, the rain falls for 8.1 days and regularly aggregates up to 1.02" (26mm) of precipitation. Throughout the year, there are 142.1 rainfall days, and 22.87" (581mm) of precipitation is accumulated.

Snowfall

Months with snowfall are January through May, September through December. September is the first month it typically snows. Throughout September, in the average 0.3 snowfall days, it receives 0.87" (22mm) of snow. In Sisters, during the entire year, snow falls for 70.7 days and aggregates up to 60.04" (1525mm) of snow.

Daylight

The average length of the day in September is 12h and 29min.
On the first day of September, sunrise is at 6:30 am and sunset at 7:41 pm. On the last day of the month, sunrise is at 7:03 am and sunset at 6:48 pm PDT.

Sunshine

The average sunshine in September in Sisters is 10.6h.

UV index

In September, the average daily maximum UV index is 3. A UV Index estimate of 3 to 5 represents a moderate threat to health from unprotected exposure to Sun's UV rays for ordinary individuals.
Note: The average daily UV index of 3 in September transforms into the following instructions:
Exercise prevention - Precautions against solar damage are endorsed. Limiting exposure to the direct Sun during midday hours can help prevent harmful UV radiation effects. Your best bet for sun defense on the face, eyes, and neck is a hat with a wide brim. Be informed! The Sun's UV radiation can be nearly doubled due to the reflection from snow.

Frequently asked questions

What are the temperatures in September?

Sisters in September has an average high-temperature of 69.8°F (21°C) and an average low-temperature of 45.1°F (7.3°C).

What is the average humidity in September?

The average relative humidity in September in Sisters is 61%.

How many days does it rain in September?

In Sisters, during September, the rain falls for 8.1 days and regularly aggregates up to 1.02" (26mm) of precipitation.

When does it start to snow?

September is the first month it typically snows. Throughout September, in the average 0.3 snowfall days, it receives 0.87" (22mm) of snow.

How many hours of daylight does Sisters have in September?

In September, the average day length is 12h and 29min.

When is the sunrise / sunset in September?

In September, on the first day of the month, sunrise is at 6:30 am and sunset at 7:41 pm. On the last day of the month, sunrise is at 7:03 am and sunset at 6:48 pm PDT.

How many hours of sunshine does Sisters have in September?

The average sunshine duration in September is 10.6h.

What is the UV index reading in September?

In Sisters, the average daily maximum UV index in September is 3. A UV Index of 3 to 5 symbolizes a moderate health threat from unprotected exposure to UV radiation.
Average humidity
Average rainfall days
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Sisters, OR

Average temperature in September - Sisters, OR
  • Average high temperature in September: 69.8°F

The warmest month (with the highest average high temperature) is July (78.8°F).
The month with the lowest average high temperature is December (36.5°F).

  • Average low temperature in September: 45.1°F

The month with the highest average low temperature is August (50.7°F).
The coldest month (with the lowest average low temperature) is December (24.8°F).

Average pressure in September
Sisters, OR

Average pressure in September - Sisters, OR
  • Average pressure in September: 30"Hg

The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is August (29.98"Hg).

Average wind speed in September
Sisters, OR

Average wind speed in September - Sisters, OR
  • Average wind speed in September: 4.8mph

The windiest month (with the highest average wind speed) is February (6.1mph).
The calmest months (with the lowest average wind speed) are August and September (4.8mph).

Average humidity in September
Sisters, OR

Average humidity in September - Sisters, OR
  • Average humidity in September: 61%

The month with the highest relative humidity is December (84%).
The months with the lowest relative humidity are July and August (53%).

Average rainfall in September
Sisters, OR

Average rainfall in September - Sisters, OR
  • Average rainfall in September: 1.02"

The wettest month (with the highest rainfall) is January (3.31").
The driest month (with the least rainfall) is July (0.35").

Average rainfall days in September
Sisters, OR

Average rainfall days in September - Sisters, OR
  • Average rainfall days in September: 8.1 days

The month with the highest number of rainy days is March (16.9 days).
The month with the least rainy days is July (5 days).

Average snowfall in September
Sisters, OR

Average snowfall in September - Sisters, OR
  • Average snowfall in September: 0.87"

The month with the highest snowfall is February (13.74").
The months with the least snowfall are June, July and August (0").

Average snowfall days in September
Sisters, OR

Average snowfall days in September - Sisters, OR
  • Average snowfall days in September: 0.3 days

The month with the highest number of snowfall days is December (14.7 days).
The months with the least snowfall days are June, July and August (0 days).

Average daylight in September /
Average sunshine in September
Sisters, OR

Average daylight in September / Average sunshine in September - Sisters, OR
  • Average daylight in September: 12h and 3min

The month with the longest days is June (Average daylight: 15h and 30min).
The month with the shortest days is December (Average daylight: 8h and 54min).

  • Average sunshine in September: 10h and 4min

The month with the most sunshine is July (Average sunshine: 12h and 0min).
The month with the least sunshine is December (Average sunshine: 5h and 6min).

Average sunshine days in September
Sisters, OR

Average sunshine days in September - Sisters, OR
  • Average sunshine days in September: 18.9 days

The month with the most sunshine days is July (23.3 days).
The month with the least sunshine days is March (8.1 days).

Average UV index in September
Sisters, OR

Average UV index in September - Sisters, OR
  • Average UV index in September: 3

The month with the highest UV index is July (UV index 6).
The month with the lowest UV index is February (UV index 1).

Average cloud cover in September
Sisters, OR

Average cloud cover in September - Sisters, OR
  • Average cloud cover in September: 21

The months with the most cloud cover are January, February, March and December (Cloud cover 49).
The month with the least cloud cover is July (Cloud cover 11).

Average visibility in September
Sisters, OR

Average visibility in September - Sisters, OR
  • Average visibility in September: 6mi

The months with the highest visibility are April, May, June, July, August, September, October and November (6mi).
The months with the lowest visibility are January, February, March and December (5mi).

Sisters, Oregon, USA

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