| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 41°F | 31°F | 1.1" |
| February | 25°F | 50°F | 37°F | 0.8" |
| March | 30°F | 59°F | 44°F | 0.8" |
| April | 34°F | 67°F | 51°F | 0.5" |
| May | 42°F | 77°F | 60°F | 1.0" |
| June | 48°F | 83°F | 67°F | 0.4" |
| July | 55°F | 93°F | 76°F | 0.1" |
| August | 53°F | 92°F | 73°F | 0.2" |
| September | 44°F | 82°F | 63°F | 0.4" |
| October | 36°F | 67°F | 50°F | 0.8" |
| November | 27°F | 52°F | 39°F | 0.9" |
| December | 20°F | 40°F | 29°F | 1.5" |
| Index | Zillah | Washington | National |
| Air quality index | 38 | 36 | 42 |
| Pollution index | 697,942 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 227 |
| Days with moderate air quality | 128 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.004% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Donald, WA | 0 | 38 | 24.0% |
| Sunnyside, WA | 16,703 | 38 | 24.0% |
| Terrace Heights, WA | 8,917 | 38 | 24.0% |
| Yakima, WA | 93,829 | 38 | 24.0% |
| Granger, WA | 3,806 | 38 | 24.0% |
| Zillah, WA | 3,137 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Knoxville, IL | 3,137 | 41 | 18.0% |
| Blanchard, LA | 3,137 | 39 | 22.0% |
| Mamou, LA | 3,137 | 41 | 18.0% |
| Elgin, OK | 3,137 | 43 | 14.0% |
| Milbank, SD | 3,137 | 25 | 50.0% |
| Zillah, WA | 3,137 | 38 | 24.0% |
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