| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 40°F | 32°F | 1.2" |
| February | 25°F | 51°F | 37°F | 1.4" |
| March | 34°F | 63°F | 48°F | 1.2" |
| April | 38°F | 67°F | 52°F | 1.9" |
| May | 46°F | 78°F | 62°F | 1.6" |
| June | 51°F | 82°F | 67°F | 2.9" |
| July | 59°F | 95°F | 77°F | 1.1" |
| August | 55°F | 92°F | 73°F | 0.4" |
| September | 45°F | 80°F | 62°F | 0.9" |
| October | 40°F | 66°F | 52°F | 1.9" |
| November | 31°F | 49°F | 40°F | 2.4" |
| December | 26°F | 40°F | 33°F | 2.5" |
| Index | Umatilla | Oregon | National |
| Air quality index | 37 | 32 | 42 |
| Pollution index | 4,405,170 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 303 |
| Days with moderate air quality | 62 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.130% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Irrigon, OR | 1,904 | 37 | 26.0% |
| Echo, OR | 577 | 38 | 24.0% |
| Hermiston, OR | 17,512 | 38 | 24.0% |
| Stanfield, OR | 2,521 | 38 | 24.0% |
| Umatilla, OR | 7,215 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Dunellen, NJ | 7,215 | 51 | 2.0% |
| Neptune Beach, FL | 7,214 | 43 | 14.0% |
| Riverdale Park, MD | 7,216 | 47 | 6.0% |
| Lago Vista, TX | 7,212 | 44 | 12.0% |
| Seward, NE | 7,210 | 31 | 38.0% |
| Umatilla, OR | 7,215 | 37 | 26.0% |
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