| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 46°F | 39°F | 3.0" |
| February | 34°F | 50°F | 41°F | 1.7" |
| March | 37°F | 54°F | 45°F | 3.4" |
| April | 40°F | 59°F | 48°F | 2.0" |
| May | 45°F | 65°F | 54°F | 2.4" |
| June | 49°F | 70°F | 59°F | 1.9" |
| July | 52°F | 77°F | 63°F | 1.3" |
| August | 52°F | 78°F | 63°F | 1.4" |
| September | 49°F | 71°F | 58°F | 2.4" |
| October | 43°F | 60°F | 50°F | 3.4" |
| November | 37°F | 52°F | 44°F | 4.0" |
| December | 32°F | 44°F | 38°F | 3.1" |
| Index | Oso | Washington | National |
| Air quality index | 24 | 36 | 42 |
| Pollution index | 15,778,900 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 361 |
| Days with moderate air quality | 4 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.270% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.160% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Canyon Creek, WA | 3,218 | 24 | 52.0% |
| Arlington, WA | 19,947 | 24 | 52.0% |
| Big Lake, WA | 2,251 | 24 | 52.0% |
| Swede Heaven, WA | 1,181 | 24 | 52.0% |
| Granite Falls, WA | 3,961 | 24 | 52.0% |
| Oso, WA | 241 | 24 | 52.0% |
| City | Population | Air Quality Index | National Avg. |
| Homewood Canyon, CA | 241 | 15 | 70.0% |
| Lanare, CA | 241 | 56 | 12.0% |
| La Motte, IA | 241 | 29 | 42.0% |
| Rose Hill, IA | 241 | 35 | 30.0% |
| Anchor, IL | 241 | 44 | 12.0% |
| Oso, WA | 241 | 24 | 52.0% |
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