September Weather in Northwest, United States

Last updated: June 24, 2025

In September, the average temperature in Northwest, United States is a comfortable 24°C (76°F). During this month, you can expect minimum temperatures to dip to around 10°C (50°F), while the maximum can soar to 34°C (94°F). The region experiences an average precipitation of 193 mm (7.6 in) over approximately 13 days, accompanied by a high average humidity of 79%. Stay prepared for a mix of warmth and humidity!

September Temperature in Northwest

In September in Northwest, the average temperature is 24°C (76°F). Maximums can reach 34°C (94°F), and minimums can be as low as 10°C (50°F). This pleasant climate makes Northwest an ideal destination for those looking to enjoy a variety of outdoor activities during this month.

September Weather in Northwest: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Northwest, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Northwest, September typically has an average temperature of 24°C (76°F), with highs reaching up to 34°C (94°F) and lows dropping to around 10°C (50°F).

Data source: Temperature data for Northwest generated using information from the Copernicus Climate Change Service.

September Precipitation in Northwest

In Northwest in September, the precipitation amount is 193 mm (7.6 in) recorded over a span of 13 days.

September Precipitation Trends in Northwest

The chart displays monthly precipitation patterns in Northwest, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Northwest, September typically receives around 193 mm (7.6 inches) of precipitation spread over approximately 13 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Northwest

In Northwest in September, humidity is 79%. With an average temperature of 24°C (76°F), this humidity feels like a thick blanket wrapped around you, making traveling somewhat uncomfortable and sticky, as you navigate through the warmth while constantly seeking shade and hydration.

September Average Humidity in Northwest

This chart illustrates the average monthly humidity levels in Northwest, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Northwest is approximately 79%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Northwest

In Northwest in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Northwest.

Maximum UV Index Levels in Northwest for September

The chart shows the monthly maximum UV Index (UVI) for Northwest in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Northwest typically reaches 9, which falls under the very high exposure category.

Data source: Northwest September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How September Weather in Northwest Compares to Other Months

Weather in Northwest varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Northwest, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Northwest, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	9°C (48°F)	70 mm (2.8 inches)	85%	moderate
February Weather	12°C (53°F)	93 mm (3.7 inches)	82%	high
March Weather	13°C (56°F)	70 mm (2.8 inches)	81%	very high
April Weather	18°C (64°F)	94 mm (3.7 inches)	80%	very high
May Weather	22°C (72°F)	120 mm (4.7 inches)	81%	extreme
June Weather	25°C (77°F)	160 mm (6.3 inches)	81%	extreme
July Weather	27°C (80°F)	171 mm (6.7 inches)	81%	extreme
August Weather	26°C (80°F)	205 mm (8.1 inches)	80%	very high
September Weather	24°C (76°F)	193 mm (7.6 inches)	79%	very high
October Weather	20°C (69°F)	64 mm (2.5 inches)	80%	very high
November Weather	13°C (55°F)	110 mm (4.3 inches)	85%	high
December Weather	10°C (51°F)	124 mm (4.9 inches)	86%	moderate