| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 56°F | 47°F | 6.0" |
| February | 39°F | 56°F | 48°F | 5.3" |
| March | 40°F | 56°F | 48°F | 6.9" |
| April | 40°F | 57°F | 49°F | 3.6" |
| May | 44°F | 59°F | 52°F | 1.2" |
| June | 47°F | 62°F | 55°F | 0.7" |
| July | 50°F | 63°F | 56°F | 0.2" |
| August | 50°F | 64°F | 57°F | 0.2" |
| September | 47°F | 65°F | 56°F | 0.5" |
| October | 45°F | 64°F | 54°F | 3.4" |
| November | 42°F | 59°F | 51°F | 5.2" |
| December | 37°F | 55°F | 47°F | 7.3" |
| Index | Arcata | 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. |
| Bayview CDP (Contra Costa County), CA | 1,753 | 27 | 46.0% |
| Fieldbrook, CA | 793 | 27 | 46.0% |
| Myrtletown, CA | 5,143 | 27 | 46.0% |
| Bayview, CA | 2,787 | 27 | 46.0% |
| Samoa, CA | 211 | 27 | 46.0% |
| Arcata, CA | 18,266 | 27 | 46.0% |
| City | Population | Air Quality Index | National Avg. |
| Hyattsville, MD | 18,267 | 47 | 6.0% |
| Bensenville, IL | 18,273 | 55 | 10.0% |
| San Carlos Park, FL | 18,256 | 36 | 28.0% |
| Schofield Barracks, HI | 18,276 | 30 | 40.0% |
| Menasha, WI | 18,280 | 37 | 26.0% |
| Arcata, CA | 18,266 | 27 | 46.0% |
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