| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 46°F | 29°F | 6.9" |
| February | 20°F | 52°F | 35°F | 9.4" |
| March | 24°F | 58°F | 40°F | 3.0" |
| April | 26°F | 60°F | 43°F | 3.9" |
| May | 31°F | 68°F | 49°F | 3.6" |
| June | 38°F | 80°F | 60°F | 1.4" |
| July | 43°F | 85°F | 65°F | 2.1" |
| August | 40°F | 83°F | 63°F | 2.0" |
| September | 35°F | 77°F | 56°F | 2.2" |
| October | 28°F | 67°F | 46°F | 4.3" |
| November | 19°F | 55°F | 35°F | 2.6" |
| December | 15°F | 47°F | 29°F | 5.7" |
| Index | Arnold | California | National |
| Air quality index | 39 | 55 | 42 |
| Pollution index | 1,641,280 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 331 |
| Days with moderate air quality | 33 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.090% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Pioneer, CA | 1,224 | 39 | 22.0% |
| Long Barn, CA | 88 | 39 | 22.0% |
| Avery, CA | 444 | 39 | 22.0% |
| Mountain Ranch, CA | 318 | 39 | 22.0% |
| Rail Road Flat, CA | 97 | 39 | 22.0% |
| Arnold, CA | 2,099 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Gurdon, AR | 2,099 | 32 | 36.0% |
| Oakland, MD | 2,099 | 36 | 28.0% |
| Hoyt Lakes, MN | 2,099 | 35 | 30.0% |
| Choctaw Lake, OH | 2,099 | 45 | 10.0% |
| Winnsboro Mills, SC | 2,099 | 43 | 14.0% |
| Arnold, CA | 2,099 | 39 | 22.0% |
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