| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 37°F | 60°F | 47°F | 5.6" |
| February | 41°F | 64°F | 52°F | 4.8" |
| March | 45°F | 69°F | 56°F | 4.6" |
| April | 47°F | 74°F | 60°F | 2.5" |
| May | 52°F | 82°F | 67°F | 0.7" |
| June | 57°F | 91°F | 74°F | 0.3" |
| July | 60°F | 96°F | 77°F | 0.0" |
| August | 59°F | 95°F | 75°F | 0.0" |
| September | 56°F | 92°F | 73°F | 0.1" |
| October | 50°F | 81°F | 64°F | 1.9" |
| November | 43°F | 68°F | 54°F | 2.3" |
| December | 37°F | 59°F | 47°F | 4.6" |
| Index | Hartley | California | National |
| Air quality index | 35 | 55 | 42 |
| Pollution index | 2,457,150 | 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 | 0.010% |
| Benzene | 0.080% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Allendale, CA | 1,429 | 35 | 30.0% |
| Lemon Hill, CA | 15,104 | 35 | 30.0% |
| Winters, CA | 7,285 | 35 | 30.0% |
| Fairfield, CA | 116,544 | 35 | 30.0% |
| Moskowite Corner, CA | 69 | 35 | 30.0% |
| Hartley, CA | 2,655 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Casey, IL | 2,655 | 40 | 20.0% |
| Wabasha, MN | 2,655 | 15 | 70.0% |
| Woodstock, NY | 2,655 | 36 | 28.0% |
| Shadybrook, TX | 2,655 | 36 | 28.0% |
| Berwick, NS | 2,655 | n/a | |
| Hartley, CA | 2,655 | 35 | 30.0% |
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