| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 36°F | 28°F | 2.0" |
| February | 25°F | 41°F | 33°F | 1.4" |
| March | 31°F | 50°F | 40°F | 2.6" |
| April | 35°F | 59°F | 47°F | 1.1" |
| May | 43°F | 70°F | 56°F | 1.4" |
| June | 50°F | 76°F | 63°F | 1.5" |
| July | 57°F | 88°F | 73°F | 0.4" |
| August | 56°F | 87°F | 71°F | 0.4" |
| September | 48°F | 76°F | 61°F | 0.6" |
| October | 38°F | 60°F | 48°F | 1.6" |
| November | 29°F | 45°F | 36°F | 2.2" |
| December | 21°F | 34°F | 28°F | 2.9" |
| Index | Malden | Washington | National |
| Air quality index | 43 | 36 | 42 |
| Pollution index | 2,233,350 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 252 |
| Days with moderate air quality | 111 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.003% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Oakesdale, WA | 420 | 18 | 64.0% |
| St. John, WA | 635 | 18 | 64.0% |
| Latah, WA | 203 | 43 | 14.0% |
| Fairfield, WA | 495 | 43 | 14.0% |
| Spangle, WA | 238 | 43 | 14.0% |
| Malden, WA | 223 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Old Harbor, AK | 223 | 31 | 38.0% |
| Bombay Beach, CA | 223 | 58 | 16.0% |
| West Point, IL | 223 | 41 | 18.0% |
| Flensburg, MN | 223 | 29 | 42.0% |
| Climax Springs, MO | 223 | 39 | 22.0% |
| Malden, WA | 223 | 43 | 14.0% |