September weather forecast
North Cascades National Park, WA

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The lovely Picture Lake reflecting the trees on the shores and the distant Mount Shuksan in the North Cascades National Park, Washington, USA
The lovely Picture Lake reflecting the trees on the shores and the distant Mount Shuksan in the North Cascades National Park, Washington, USA

Weather in September

In September, the weather starts to cool down from the highs of the previous two months in North Cascades National Park. The reduction in temperature signals the approaching autumn season. Despite the cooler air, there’s still plenty of daylight and sunshine hours permitting a multitude of outdoor activities. It is still possible to enjoy hiking and camping, given the decent weather and the scenic fall colors beginning to show. However, rainfall starts to increase after the summer lull, marking the beginning of the wet season.

Temperature

During the transition into September, North Cascades National Park observes a decrease in the average high-temperature, falling from a pleasant 69.8°F (21°C) in August to a comfortable 60.8°F (16°C). During September, North Cascades National Park reports a marked contrast from daily peak temperatures, with an average nighttime reading of 39.2°F (4°C).

Rainfall

In North Cascades National Park, in September, during 11 rainfall days, 2.52" (64mm) of precipitation is typically accumulated. Throughout the year, in North Cascades National Park, there are 157 rainfall days, and 51.02" (1296mm) of precipitation is accumulated.

Daylight

The average length of the day in September is 12h and 34min.
On the first day of the month, sunrise is at 6:23 am and sunset at 7:46 pm. On the last day of September, in North Cascades National Park, sunrise is at 7:04 am and sunset at 6:45 pm PDT.

Sunshine

In North Cascades National Park, the average sunshine in September is 6h.

UV index

In North Cascades National Park, Washington, the average daily maximum UV index in September is 5. A UV Index value of 3 to 5 symbolizes a moderate health risk from exposure to the Sun's UV rays for the average person.
Note: The UV index of 5 during September translates into the following guidance:
Take necessary precautions - Suggestions to elude sunburn are provided. The Sun's harshest UV rays are around midday; it's wise to seek shade and limit time outdoors. For a sun-safe wardrobe, go for clothes that are tightly woven and generously sized.
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Frequently asked questions

What is the usual temperature for North Cascades National Park in September?

The high-temperature, in September, in North Cascades National Park, records 60.8°F (16°C), while the low-temperature is 39.2°F (4°C).

How many days does it rain in September in North Cascades National Park?

In September, in North Cascades National Park, Washington, the rain falls for 11 days. Throughout September, 2.52" (64mm) of precipitation is accumulated.

How many hours of daylight does North Cascades National Park have in September?

The average day length in September is 12h and 34min.

What time are sunrise and sunset in September in North Cascades National Park?

On the first day of September in North Cascades National Park, sunrise is at 6:23 am and sunset at 7:46 pm. On the last day of the month, sunrise is at 7:04 am and sunset at 6:45 pm PDT.

How many hours of sunshine does North Cascades National Park have in September?

In September, the average sunshine duration in North Cascades National Park is 6h.

What is the UV index reading in September in North Cascades National Park?

The average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a moderate health threat from unsafe exposure to Sun's UV rays.
Average low temperature
Average rainfall days
Average daylight
Average sunshine
Average UV index

Average temperature in September
North Cascades National Park, WA

Average temperature in September - North Cascades National Park, WA
  • Average high temperature in September: 61°F

The warmest months (with the highest average high temperature) are July and August (70°F).
The months with the lowest average high temperature are January and December (30°F).

  • Average low temperature in September: 39°F

The months with the highest average low temperature are July and August (45°F).
The coldest months (with the lowest average low temperature) are January and December (18°F).

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Average rainfall in September
North Cascades National Park, WA

Average rainfall in September - North Cascades National Park, WA
  • Average rainfall in September: 2.5"

The wettest month (with the highest rainfall) is December (7.8").
The driest months (with the least rainfall) are July and August (1.7").

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Average rainfall days in September
North Cascades National Park, WA

Average rainfall days in September - North Cascades National Park, WA
  • Average rainfall days in September: 11 days

The month with the highest number of rainy days is December (18 days).
The month with the least rainy days is July (8 days).

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Average daylight in September /
Average sunshine in September
North Cascades National Park, WA

Average daylight in September / Average sunshine in September - North Cascades National Park, WA
  • Average daylight in September: 12h and 4min

The month with the longest days is June (Average daylight: 16h and 6min).
The month with the shortest days is December (Average daylight: 8h and 18min).

  • Average sunshine in September: 6h

The month with the most sunshine is July (Average sunshine: 9h).
The months with the least sunshine are January, November and December (Average sunshine: 2h).

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Average UV index in September
North Cascades National Park, WA

Average UV index in September - North Cascades National Park, WA
  • Average UV index in September: 5

The months with the highest UV index are June, July and August (UV index 7).
The months with the lowest UV index are January, November and December (UV index 1).

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North Cascades National Park, Washington, USA

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