| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 45°F | 69°F | 56°F | 7.4" |
| February | 47°F | 68°F | 57°F | 5.5" |
| March | 50°F | 71°F | 60°F | 2.6" |
| April | 52°F | 73°F | 62°F | 1.3" |
| May | 57°F | 74°F | 64°F | 2.3" |
| June | 60°F | 77°F | 67°F | 0.1" |
| July | 64°F | 81°F | 71°F | 0.5" |
| August | 64°F | 83°F | 72°F | 0.2" |
| September | 62°F | 84°F | 71°F | 5.2" |
| October | 57°F | 80°F | 67°F | 1.7" |
| November | 50°F | 74°F | 61°F | 2.9" |
| December | 44°F | 67°F | 55°F | 7.6" |
| Index | Westminster | California | National |
| Air quality index | 72 | 55 | 50 |
| Pollution index | 858,652 | 18,106,726 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 66 |
| Days with moderate air quality | 208 |
| Days w/ poor A.Q. for sensitive groups | 62 |
| Days with unhealthy air quality | 28 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.020% |
| Mercury | 0.001% |
| City, State | Population | Air Quality Index | National Avg. |
| Cudahy, CA | 24,106 | 72 | 44% |
| Paramount, CA | 54,941 | 72 | 44% |
| Willowbrook, CA | 22,035 | 72 | 44% |
| Cypress, CA | 48,978 | 72 | 44% |
| La Habra, CA | 61,660 | 72 | 44% |
| Westminster, CA | 91,635 | 72 | 44% |
| City, State | Population | Air Quality Index | National Avg. |
| Boca Raton, FL | 91,702 | 41 | 18% |
| Miami Beach, FL | 91,784 | 41 | 18% |
| San Marcos, CA | 91,479 | 64 | 28% |
| Redding, CA | 91,320 | 42 | 16% |
| Lynn, MA | 92,074 | 43 | 14% |
| Westminster, CA | 91,635 | 72 | 44% |
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