Weather history and climate summary information is available for the following locations:
- Bellingham
- Grant County Airport
- Seattle
- Spokane
- Tacoma
- Walla Walla
- Yakima
Warmest September Days
The warmest September days in Washington are:
| Grant County Airport, Washington | 1988 | 109°F |
| Walla Walla, Washington | 1987 | 102.9°F |
| Grant County Airport, Washington | 1987 | 102.9°F |
| Walla Walla, Washington | 1998 | 102.2°F |
| Walla Walla, Washington | 1950 | 102°F |
Coldest September Days
The coldest September days in Washington were:
| Spokane, Washington | 2000 | 21.9°F |
| Spokane, Washington | 1983 | 24.1°F |
| Spokane, Washington | 1985 | 24.1°F |
| Yakima, Washington | 1985 | 24.1°F |
| Yakima, Washington | 2000 | 25°F |
Wettest September Days
The wettest single days in September occurred:
| Seattle, Washington | 1978 | 12.1 inches |
| Seattle, Washington | 1953 | 1.9 inches |
| Seattle, Washington | 2010 | 1.8 inches |
| Walla Walla, Washington | 2003 | 1.7 inches |
| Seattle, Washington | 1953 | 1.7 inches |