Contents
- Weather in September
- Frequently asked questions
- Average temperature in September
- Average pressure in September
- Average wind speed in September
- Average humidity in September
- Average rainfall in September
- Average rainfall days in September
- Average snowfall in September
- Average snowfall days in September
- Average daylight in September
- Average sunshine in September
- Average sunshine days in September
- Average UV index in September
- Average cloud cover in September
- Average visibility in September
Weather in September
Temperature
A change in temperatures is noted as August gives way to September, with average highs reducing from a tropical 88.3°F (31.3°C) to a warm 76.1°F (24.5°C). During the nights in September, the temperature averages to a fresh 54.7°F (12.6°C).Humidity
In September, the average relative humidity is 45%.Rainfall
In Mattawa, in September, during 4.1 rainfall days, 0.31" (8mm) of precipitation is typically accumulated. Throughout the year, there are 86.4 rainfall days, and 6.38" (162mm) of precipitation is accumulated.Snowfall
Months with snowfall are January through April, September, November and December. September is the first month it typically snows. Throughout September, in the average 0.1 snowfall days, it receives 0.04" (1mm) of snow. Throughout the year, there are 22.3 snowfall days, and 10" (254mm) of snow is accumulated.Daylight
The average length of the day in September is 12h and 32min.On the first day of September, sunrise is at 6:20 am and sunset at 7:38 pm. On the last day of the month, sunrise is at 6:58 am and sunset at 6:40 pm PDT.
Sunshine
In September, the average sunshine is 10.8h.UV index
The average daily maximum UV index in September is 4. A UV Index value of 3 to 5 symbolizes a moderate health risk from exposure to the Sun's UV rays for ordinary individuals.Note: In September, the maximum UV index of 4 translates into these guidelines:
Take heed. Individuals of lighter complexion can be burned in less than half an hour. Direct exposure to the Sun's intense radiation around midday should be avoided for health reasons. Arm yourself against UV rays' harm with protective apparel and UV-filtering shades. Heed this! Snow reflection can almost augment the UV radiation of the sun by double.
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Data Sources | Weather Forecasting & Climate
Frequently asked questions
What are September temperatures?
What is the average humidity in September?
How many days does it rain in September?
When does it start to snow?
How many hours of daylight does Mattawa have in September?
When is the sunrise / sunset in September?
How many hours of sunshine does Mattawa have in September?
What is the UV index intensity in September?
Average temperature in September
Mattawa, WA
- Average high temperature in September: 76.1°F
The warmest months (with the highest average high temperature) are July and August (88.3°F).
The month with the lowest average high temperature is December (34.5°F).
- Average low temperature in September: 54.7°F
The month with the highest average low temperature is August (61.5°F).
The coldest month (with the lowest average low temperature) is December (24.3°F).
Average pressure in September
Mattawa, WA
- Average pressure in September: 29.96"Hg
The month with the highest atmospheric pressure is January (30.17"Hg).
The month with the lowest atmospheric pressure is August (29.91"Hg).
Average wind speed in September
Mattawa, WA
- Average wind speed in September: 6.3mph
The windiest month (with the highest average wind speed) is April (7.6mph).
The calmest month (with the lowest average wind speed) is December (4.7mph).
Average humidity in September
Mattawa, WA
- Average humidity in September: 45%
The month with the highest relative humidity is January (83%).
The month with the lowest relative humidity is July (37%).
Average rainfall in September
Mattawa, WA
- Average rainfall in September: 0.31"
The wettest months (with the highest rainfall) are January and December (0.87").
The driest month (with the least rainfall) is August (0.2").
Average rainfall days in September
Mattawa, WA
- Average rainfall days in September: 4.1 days
The month with the highest number of rainy days is March (10.6 days).
The month with the least rainy days is August (3.5 days).
Average snowfall in September
Mattawa, WA
- Average snowfall in September: 0.04"
The month with the highest snowfall is December (3.43").
The months with the least snowfall are May, June, July, August and October (0").
Average snowfall days in September
Mattawa, WA
- Average snowfall days in September: 0.1 days
The month with the highest number of snowfall days is December (6.5 days).
The months with the least snowfall days are May, June, July and August (0 days).
Average daylight in September /
Average sunshine in September
Mattawa, WA
- Average daylight in September: 12h and 3min
The month with the longest days is June (Average daylight: 15h and 48min).
The month with the shortest days is December (Average daylight: 8h and 36min).
- Average sunshine in September: 10h and 5min
The months with the most sunshine are July and August (Average sunshine: 12h and 0min).
The month with the least sunshine is January (Average sunshine: 4h and 54min).
Average sunshine days in September
Mattawa, WA
- Average sunshine days in September: 24.3 days
The months with the most sunshine days are July and August (25.8 days).
The month with the least sunshine days is February (16 days).
Average UV index in September
Mattawa, WA
- Average UV index in September: 4
The month with the highest UV index is July (UV index 7).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Mattawa, WA
- Average cloud cover in September: 16
The month with the most cloud cover is January (Cloud cover 47).
The months with the least cloud cover are July and August (Cloud cover 10).
Average visibility in September
Mattawa, WA
- Average visibility in September: 6mi
The months with the highest visibility are February, March, April, May, June, July, August, September, October and November (6mi).
The months with the lowest visibility are January and December (5mi).
Mattawa, Washington, USA
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