| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 53°F | 44°F | 6.0" |
| February | 40°F | 56°F | 49°F | 6.4" |
| March | 41°F | 57°F | 50°F | 6.8" |
| April | 40°F | 56°F | 49°F | 5.8" |
| May | 45°F | 59°F | 53°F | 3.6" |
| June | 47°F | 61°F | 55°F | 3.9" |
| July | 52°F | 65°F | 58°F | 1.0" |
| August | 50°F | 63°F | 56°F | 0.3" |
| September | 46°F | 63°F | 54°F | 0.4" |
| October | 44°F | 61°F | 53°F | 5.6" |
| November | 40°F | 58°F | 49°F | 4.0" |
| December | 39°F | 54°F | 47°F | 11.4" |
| Index | Fortuna | California | National |
| Air quality index | 27 | 55 | 42 |
| Pollution index | 5,642,310 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 353 |
| Days with moderate air quality | 10 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.080% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.050% |
| Mercury | 0.050% |
| City | Population | Air Quality Index | National Avg. |
| Hydesville, CA | 1,051 | 27 | 46.0% |
| Rio Dell, CA | 3,388 | 27 | 46.0% |
| Ferndale, CA | 1,387 | 27 | 46.0% |
| Bayview CDP (Contra Costa County), CA | 1,753 | 27 | 46.0% |
| Myrtletown, CA | 5,143 | 27 | 46.0% |
| Fortuna, CA | 12,135 | 27 | 46.0% |
| City | Population | Air Quality Index | National Avg. |
| Baraboo, WI | 12,133 | 35 | 30.0% |
| Sylacauga, AL | 12,132 | 38 | 24.0% |
| Cascades, VA | 12,132 | 47 | 6.0% |
| Somerville, NJ | 12,139 | 41 | 18.0% |
| Lake Tapps, WA | 12,129 | 45 | 10.0% |
| Fortuna, CA | 12,135 | 27 | 46.0% |
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