| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 58°F | 47°F | 3.8" |
| February | 39°F | 62°F | 50°F | 3.4" |
| March | 41°F | 66°F | 52°F | 3.0" |
| April | 42°F | 69°F | 55°F | 1.6" |
| May | 46°F | 74°F | 59°F | 0.5" |
| June | 50°F | 80°F | 64°F | 0.3" |
| July | 53°F | 81°F | 65°F | 0.0" |
| August | 53°F | 80°F | 64°F | 0.0" |
| September | 49°F | 82°F | 64°F | 0.1" |
| October | 45°F | 76°F | 59°F | 1.3" |
| November | 40°F | 66°F | 52°F | 1.8" |
| December | 36°F | 58°F | 47°F | 3.8" |
| Index | Napa | California | National |
| Air quality index | 35 | 55 | 42 |
| Pollution index | 7,123,510 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 330 |
| Days with moderate air quality | 31 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.110% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.090% |
| Mercury | 0.050% |
| City | Population | Air Quality Index | National Avg. |
| Glen Ellen, CA | 1,214 | 34 | 32.0% |
| St. Helena, CA | 6,049 | 34 | 32.0% |
| Kenwood, CA | 540 | 34 | 32.0% |
| Boyes Hot Springs, CA | 8,006 | 35 | 30.0% |
| Lemon Hill, CA | 15,104 | 35 | 30.0% |
| Napa, CA | 78,294 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Boynton Beach, FL | 78,060 | 41 | 18.0% |
| Parma, OH | 78,623 | 50 | = 100 |
| Pharr, TX | 78,689 | 42 | 16.0% |
| Lake Charles, LA | 77,832 | 45 | 10.0% |
| Flower Mound, TX | 78,854 | 51 | 2.0% |
| Napa, CA | 78,294 | 35 | 30.0% |
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