Grand Coulee Weather in September
Average highs run from 82°F on September 1 to 70°F on September 30, and lows from 55°F to 46°F. Normal precipitation for the month is 0.36 in over about 4 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 77°F
- Average low
- 51°F
- Precipitation
- 0.36 in
- Record high
- 104°FSep 2, 1938
- Record low
- 30°FSep 23, 1970
- Chance of a freeze
- 1%
- Days of 90°F or more
- 2.2
- Daylight
- 13 h 23 min to 11 h 43 min
- Cloud cover
- 45%
- Humidity
- 52%
- Dew point
- 40°F
- Wind
- 6.0 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation.
| Date | Normal high | Normal low | Record high | Record low | Chance wet |
|---|---|---|---|---|---|
| Sep 1 | 82°F | 55°F | 102°F 1938 | 39°F 1951 | 11% |
| Sep 2 | 82°F | 54°F | 104°F 1938 | 40°F 1951 | 11% |
| Sep 3 | 82°F | 54°F | 103°F 1988 | 38°F 1951 | 11% |
| Sep 4 | 81°F | 54°F | 101°F 1988 | 37°F 1951 | 11% |
| Sep 5 | 81°F | 54°F | 99°F 1934 | 40°F 1951 | 12% |
| Sep 6 | 81°F | 53°F | 97°F 1944 | 38°F 1992 | 12% |
| Sep 7 | 80°F | 53°F | 96°F 1944 | 36°F 1984 | 12% |
| Sep 8 | 80°F | 53°F | 97°F 1935 | 40°F 1951 | 12% |
| Sep 9 | 80°F | 53°F | 99°F 1935 | 40°F 1951 | 12% |
| Sep 10 | 79°F | 52°F | 96°F 1935 | 42°F 1978 | 13% |
| Sep 11 | 79°F | 52°F | 99°F 1940 | 39°F 1986 | 13% |
| Sep 12 | 79°F | 52°F | 95°F 1937 | 38°F 1978 | 13% |
| Sep 13 | 78°F | 51°F | 95°F 1937 | 31°F 1970 | 13% |
| Sep 14 | 78°F | 51°F | 98°F 1938 | 36°F 1978 | 14% |
| Sep 15 | 77°F | 51°F | 99°F 1938 | 40°F 1970 | 14% |
| Sep 16 | 77°F | 51°F | 100°F 1938 | 34°F 1965 | 14% |
| Sep 17 | 77°F | 50°F | 99°F 1938 | 35°F 1965 | 14% |
| Sep 18 | 76°F | 50°F | 100°F 1938 | 34°F 2002 | 15% |
| Sep 19 | 76°F | 50°F | 94°F 1950 | 38°F 1957 | 15% |
| Sep 20 | 75°F | 49°F | 96°F 1939 | 36°F 1983 | 15% |
| Sep 21 | 75°F | 49°F | 96°F 1950 | 38°F 1970 | 15% |
| Sep 22 | 74°F | 49°F | 94°F 1938 | 35°F 1970 | 15% |
| Sep 23 | 74°F | 48°F | 91°F 1939 | 30°F 1970 | 16% |
| Sep 24 | 73°F | 48°F | 90°F 1952 | 32°F 2000 | 16% |
| Sep 25 | 73°F | 48°F | 94°F 1952 | 32°F 1972 | 16% |
| Sep 26 | 72°F | 47°F | 89°F 1950 | 37°F 1945 | 17% |
| Sep 27 | 72°F | 47°F | 88°F 1967 | 33°F 1972 | 17% |
| Sep 28 | 71°F | 47°F | 88°F 1963 | 34°F 1983 | 17% |
| Sep 29 | 71°F | 46°F | 90°F 1935 | 30°F 1982 | 18% |
| Sep 30 | 70°F | 46°F | 92°F 1935 | 30°F 1974 | 18% |
Chance of rain
- Chance of a wet day
Sunrise and sunset
Times for 2026, local time (PDT).
- September 1
- sunrise 6:14 AM, sunset 7:37 PM
- September 30
- sunrise 6:54 AM, sunset 6:37 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00451767 (Coulee Dam 1 Sw), public domain. Records: NOAA GHCN-Daily, station USC00451767, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.