| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 47°F | 40°F | 8.3" |
| February | 36°F | 52°F | 42°F | 5.4" |
| March | 40°F | 56°F | 46°F | 6.0" |
| April | 41°F | 62°F | 50°F | 4.8" |
| May | 47°F | 69°F | 56°F | 5.7" |
| June | 52°F | 73°F | 60°F | 3.6" |
| July | 55°F | 80°F | 65°F | 2.1" |
| August | 55°F | 81°F | 66°F | 2.8" |
| September | 51°F | 75°F | 61°F | 5.1" |
| October | 46°F | 63°F | 53°F | 6.4" |
| November | 40°F | 52°F | 45°F | 8.2" |
| December | 35°F | 45°F | 39°F | 8.9" |
| Index | Winlock | Washington | National |
| Air quality index | 20 | 36 | 42 |
| Pollution index | 4,215,410 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 343 |
| Days with moderate air quality | 22 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.005% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.250% |
| City | Population | Air Quality Index | National Avg. |
| Vader, WA | 696 | 18 | 64.0% |
| Ryderwood, WA | 401 | 18 | 64.0% |
| Onalaska, WA | 431 | 20 | 60.0% |
| Toledo, WA | 532 | 20 | 60.0% |
| Chehalis, WA | 7,607 | 20 | 60.0% |
| Winlock, WA | 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% |
| Winlock, WA | 1,740 | 20 | 60.0% |
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