| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 60°F | 47°F | 5.0" |
| February | 39°F | 64°F | 51°F | 4.6" |
| March | 42°F | 68°F | 54°F | 4.3" |
| April | 45°F | 74°F | 59°F | 2.5" |
| May | 53°F | 84°F | 69°F | 1.4" |
| June | 61°F | 94°F | 77°F | 1.0" |
| July | 66°F | 102°F | 84°F | 0.1" |
| August | 63°F | 100°F | 82°F | 0.0" |
| September | 57°F | 94°F | 75°F | 0.5" |
| October | 49°F | 80°F | 64°F | 2.2" |
| November | 40°F | 67°F | 52°F | 3.5" |
| December | 36°F | 58°F | 46°F | 6.1" |
| Index | Lewiston | California | National |
| Air quality index | 42 | 55 | 42 |
| Pollution index | 5,642,310 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 311 |
| Days with moderate air quality | 53 |
| 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. |
| Junction City, CA | 754 | 42 | 16.0% |
| Weaverville, CA | 3,308 | 42 | 16.0% |
| Douglas City, CA | 678 | 42 | 16.0% |
| French Gulch, CA | 441 | 42 | 16.0% |
| Lewiston, CA | 1,481 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| St. David, AZ | 1,481 | 45 | 10.0% |
| Greenfield, IL | 1,481 | 40 | 20.0% |
| Markle, IN | 1,481 | 31 | 38.0% |
| Beattyville, KY | 1,481 | 33 | 34.0% |
| Tarkio, MO | 1,481 | 43 | 14.0% |
| Lewiston, CA | 1,481 | 42 | 16.0% |
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