| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 43°F | 34°F | 1.8" |
| February | 30°F | 47°F | 38°F | 1.0" |
| March | 34°F | 54°F | 42°F | 1.4" |
| April | 36°F | 59°F | 46°F | 1.7" |
| May | 42°F | 68°F | 54°F | 2.7" |
| June | 49°F | 77°F | 62°F | 2.4" |
| July | 56°F | 90°F | 73°F | 2.0" |
| August | 55°F | 88°F | 71°F | 2.1" |
| September | 48°F | 80°F | 63°F | 1.7" |
| October | 41°F | 64°F | 51°F | 2.1" |
| November | 33°F | 50°F | 40°F | 1.4" |
| December | 26°F | 40°F | 32°F | 1.2" |
| Index | John Day | Oregon | National |
| Air quality index | 20 | 32 | 42 |
| Pollution index | 3,459,540 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 344 |
| Days with moderate air quality | 21 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.004% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Canyon City, OR | 807 | 20 | 60.0% |
| Mount Vernon, OR | 786 | 20 | 60.0% |
| Prairie City, OR | 757 | 20 | 60.0% |
| John Day, OR | 1,740 | 20 | 60.0% |
| City | Population | Air Quality Index | National Avg. |
| Blackwater, AZ | 1,740 | 74 | 48.0% |
| Boronda, CA | 1,740 | 37 | 26.0% |
| Fern Acres, HI | 1,740 | 16 | 68.0% |
| Wilder, ID | 1,740 | 36 | 28.0% |
| Charlotte Hall, MD | 1,740 | 47 | 6.0% |
| John Day, OR | 1,740 | 20 | 60.0% |
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