| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 46°F | 39°F | 4.4" |
| February | 35°F | 50°F | 41°F | 3.0" |
| March | 38°F | 53°F | 45°F | 4.1" |
| April | 41°F | 58°F | 49°F | 2.9" |
| May | 46°F | 65°F | 55°F | 2.3" |
| June | 51°F | 69°F | 59°F | 1.6" |
| July | 54°F | 74°F | 63°F | 0.7" |
| August | 54°F | 75°F | 63°F | 0.9" |
| September | 49°F | 69°F | 58°F | 2.1" |
| October | 43°F | 60°F | 51°F | 4.0" |
| November | 38°F | 51°F | 44°F | 5.2" |
| December | 33°F | 45°F | 38°F | 4.2" |
| Index | Ferndale | Washington | National |
| Air quality index | 34 | 36 | 42 |
| Pollution index | 480,925 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 277 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.040% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Custer, WA | 298 | 34 | 32.0% |
| Sudden Valley, WA | 7,407 | 34 | 32.0% |
| Lynden, WA | 14,700 | 34 | 32.0% |
| Everson, WA | 2,773 | 34 | 32.0% |
| Sumas, WA | 1,405 | 34 | 32.0% |
| Ferndale, WA | 14,591 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Greenlawn, NY | 14,598 | 43 | 14.0% |
| Homosassa Springs, FL | 14,566 | 30 | 40.0% |
| Thibodaux, LA | 14,565 | 41 | 18.0% |
| Yankton, SD | 14,619 | 36 | 28.0% |
| Roanoke Rapids, NC | 14,562 | 36 | 28.0% |
| Ferndale, WA | 14,591 | 34 | 32.0% |
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