| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 57°F | 47°F | 10.1" |
| February | 41°F | 62°F | 51°F | 8.0" |
| March | 44°F | 67°F | 55°F | 8.4" |
| April | 46°F | 74°F | 59°F | 4.6" |
| May | 53°F | 83°F | 68°F | 2.6" |
| June | 58°F | 91°F | 75°F | 2.6" |
| July | 62°F | 96°F | 79°F | 0.2" |
| August | 60°F | 95°F | 77°F | 0.4" |
| September | 57°F | 90°F | 73°F | 1.3" |
| October | 50°F | 79°F | 63°F | 4.8" |
| November | 43°F | 65°F | 53°F | 7.5" |
| December | 37°F | 56°F | 46°F | 9.8" |
| Index | Newcastle | California | National |
| Air quality index | 52 | 55 | 42 |
| Pollution index | 4,289,310 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 171 |
| Days with moderate air quality | 173 |
| Days w/ poor A.Q. for sensitive groups | 21 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.050% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.060% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Meadow Vista, CA | 3,508 | 44 | 12.0% |
| Sheridan, CA | 1,120 | 44 | 12.0% |
| Lake of the Pines, CA | 4,350 | 44 | 12.0% |
| Citrus Heights, CA | 87,665 | 52 | 4.0% |
| Granite Bay, CA | 22,818 | 52 | 4.0% |
| Newcastle, CA | 1,360 | 52 | 4.0% |
| City | Population | Air Quality Index | National Avg. |
| Hays, NC | 1,360 | 26 | 48.0% |
| Gillam, MB | 1,360 | n/a | |
| Garberville, CA | 1,361 | 27 | 46.0% |
| Sanborn, IA | 1,359 | 36 | 28.0% |
| Dayton, IN | 1,359 | 42 | 16.0% |
| Newcastle, CA | 1,360 | 52 | 4.0% |
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