| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 46°F | 34°F | 1.7" |
| February | 27°F | 53°F | 39°F | 1.5" |
| March | 31°F | 58°F | 43°F | 1.5" |
| April | 33°F | 64°F | 48°F | 1.0" |
| May | 40°F | 74°F | 57°F | 0.9" |
| June | 47°F | 83°F | 65°F | 0.8" |
| July | 55°F | 94°F | 75°F | 0.2" |
| August | 52°F | 93°F | 73°F | 0.2" |
| September | 45°F | 85°F | 64°F | 0.2" |
| October | 37°F | 70°F | 52°F | 1.3" |
| November | 30°F | 54°F | 41°F | 1.5" |
| December | 25°F | 45°F | 34°F | 2.2" |
| Index | Yreka | California | National |
| Air quality index | 36 | 55 | 42 |
| Pollution index | 13,842,600 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 295 |
| Days with moderate air quality | 63 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 4 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.210% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.030% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Gazelle, CA | 111 | 36 | 28.0% |
| Montague, CA | 1,519 | 36 | 28.0% |
| Greenview, CA | 139 | 36 | 28.0% |
| Grenada, CA | 295 | 36 | 28.0% |
| Fort Jones, CA | 578 | 36 | 28.0% |
| Yreka, CA | 7,589 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Corning, CA | 7,589 | 41 | 18.0% |
| Princeton, IL | 7,589 | 0 | 100.0% |
| Sioux Center, IA | 7,592 | 35 | 30.0% |
| Clear Lake, IA | 7,594 | 15 | 70.0% |
| Glen Ridge, NJ | 7,583 | 51 | 2.0% |
| Yreka, CA | 7,589 | 36 | 28.0% |
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