| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 40°F | 56°F | 47°F | 14.3" |
| February | 41°F | 56°F | 47°F | 10.3" |
| March | 42°F | 56°F | 48°F | 14.1" |
| April | 43°F | 59°F | 50°F | 9.9" |
| May | 47°F | 64°F | 54°F | 6.0" |
| June | 50°F | 68°F | 58°F | 8.1" |
| July | 52°F | 69°F | 59°F | 2.7" |
| August | 52°F | 69°F | 59°F | 1.5" |
| September | 52°F | 71°F | 59°F | 6.0" |
| October | 49°F | 66°F | 56°F | 11.9" |
| November | 44°F | 58°F | 50°F | 14.5" |
| December | 40°F | 54°F | 46°F | 14.1" |
| Index | O'Brien | Oregon | National |
| Air quality index | 26 | 32 | 42 |
| Pollution index | 13,842,600 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 283 |
| Days with moderate air quality | 77 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.210% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.030% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Kerby, OR | 288 | 26 | 48.0% |
| Selma, OR | 946 | 26 | 48.0% |
| Takilma, OR | 483 | 26 | 48.0% |
| Cave Junction, OR | 2,226 | 26 | 48.0% |
| O'Brien, OR | 660 | 26 | 48.0% |
| City | Population | Air Quality Index | National Avg. |
| Jacksons' Gap, AL | 660 | 38 | 24.0% |
| Inyokern, CA | 660 | 67 | 34.0% |
| Coalville, IA | 660 | 37 | 26.0% |
| Moulton, IA | 660 | 29 | 42.0% |
| Fordsville, KY | 660 | 43 | 14.0% |
| O'Brien, OR | 660 | 26 | 48.0% |