| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 43°F | 34°F | 1.3" |
| February | 29°F | 49°F | 38°F | 1.0" |
| March | 33°F | 58°F | 45°F | 1.6" |
| April | 36°F | 64°F | 50°F | 1.2" |
| May | 43°F | 74°F | 58°F | 1.4" |
| June | 49°F | 81°F | 65°F | 1.3" |
| July | 56°F | 92°F | 75°F | 0.2" |
| August | 55°F | 91°F | 73°F | 0.3" |
| September | 48°F | 80°F | 63°F | 0.5" |
| October | 39°F | 66°F | 51°F | 1.1" |
| November | 31°F | 52°F | 41°F | 1.4" |
| December | 25°F | 41°F | 32°F | 1.9" |
| Index | Pendleton | Oregon | National |
| Air quality index | 38 | 32 | 42 |
| Pollution index | 4,405,170 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 286 |
| Days with moderate air quality | 72 |
| Days w/ poor A.Q. for sensitive groups | 6 |
| Days with unhealthy air quality |
| 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. |
| Kirkpatrick, OR | 223 | 38 | 24.0% |
| Pilot Rock, OR | 1,293 | 38 | 24.0% |
| Mission, OR | 888 | 38 | 24.0% |
| Cayuse, OR | 61 | 38 | 24.0% |
| Gopher Flats, OR | 327 | 38 | 24.0% |
| Pendleton, OR | 16,685 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Mount Vernon, OH | 16,684 | 41 | 18.0% |
| Tahlequah, OK | 16,684 | 36 | 28.0% |
| North Myrtle Beach, SC | 16,684 | 14 | 72.0% |
| Opelousas, LA | 16,687 | 41 | 18.0% |
| Sylvan Lake, AB | 16,694 | n/a | |
| Pendleton, OR | 16,685 | 38 | 24.0% |
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