Last updated: June 24, 2025
In September, the average temperature in Grand Coulee, United States hovers around 17°C (62°F). Expect a minimum of 2°C (36°F) and a maximum of 35°C (95°F), giving you a taste of the season's variety. Precipitation is modest, with an average of 24 mm (1.0 in) over 3 days, and the air carries a comfortable 60% humidity. Whether you're enjoying the warmth or braving the chill, there's a unique charm to the weather this month!
In September in Grand Coulee, the average temperature is 17°C (62°F). Maximums can reach 35°C (95°F) and minimums can be as low as 2°C (36°F). This variation in temperature makes Grand Coulee a destination that requires layered clothing and preparations for both warm and cooler periods during your trip.
In Grand Coulee in September, the total precipitation amount is 24 mm (1.0 in) accumulated over a period of 3 days.
In Grand Coulee in September humidity is 60%. With an average temperature of 17°C (62°F), this humidity feels like a refreshing embrace, making travel both comfortable and invigorating as you explore the sights without feeling overly sticky or uncomfortable.
In Grand Coulee in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Grand Coulee.
UV Risk Categories
Weather in Grand Coulee varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Grand Coulee, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -2°C (28°F) | 67 mm (2.6 inches) | 85% | low |
| February Weather | -2°C (28°F) | 47 mm (1.9 inches) | 86% | moderate |
| March Weather | 4°C (39°F) | 46 mm (1.8 inches) | 86% | moderate |
| April Weather | 9°C (48°F) | 39 mm (1.6 inches) | 82% | high |
| May Weather | 15°C (59°F) | 37 mm (1.4 inches) | 77% | very high |
| June Weather | 20°C (68°F) | 13 mm (0.5 inches) | 79% | very high |
| July Weather | 24°C (75°F) | 4 mm (0.1 inches) | 77% | very high |
| August Weather | 23°C (74°F) | 8 mm (0.3 inches) | 62% | very high |
| September Weather | 17°C (62°F) | 24 mm (1.0 inches) | 60% | high |
| October Weather | 8°C (48°F) | 42 mm (1.7 inches) | 80% | moderate |
| November Weather | 3°C (37°F) | 51 mm (2.0 inches) | 87% | moderate |
| December Weather | -2°C (29°F) | 57 mm (2.2 inches) | 86% | low |