| 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 | Nicasio | California | National |
| Air quality index | 40 | 55 | 42 |
| Pollution index | 7,898,290 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 290 |
| Days with moderate air quality | 74 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.260% |
| Benzene | 0.080% |
| Carbon Tetrachloride | 0.005% |
| Lead | 0.240% |
| Mercury | 0.270% |
| City | Population | Air Quality Index | National Avg. |
| Tomales, CA | 160 | 34 | 32.0% |
| Dillon Beach, CA | 309 | 34 | 32.0% |
| Petaluma, CA | 60,865 | 34 | 32.0% |
| Point Reyes Station, CA | 210 | 34 | 32.0% |
| Temelec, CA | 1,915 | 35 | 30.0% |
| Nicasio, CA | 123 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Cold Bay, AK | 123 | 31 | 38.0% |
| Blue Mountain, AR | 123 | 36 | 28.0% |
| Vincent, IA | 123 | 37 | 26.0% |
| Princeton, ID | 123 | 10 | 80.0% |
| Raritan, IL | 123 | 29 | 42.0% |
| Nicasio, CA | 123 | 40 | 20.0% |
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