| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 41°F | 66°F | 52°F | 10.0" |
| February | 44°F | 68°F | 54°F | 5.7" |
| March | 46°F | 75°F | 58°F | 2.7" |
| April | 47°F | 78°F | 60°F | 1.7" |
| May | 53°F | 83°F | 66°F | 2.2" |
| June | 55°F | 88°F | 70°F | 1.2" |
| July | 63°F | 96°F | 78°F | 0.0" |
| August | 63°F | 96°F | 78°F | 0.1" |
| September | 56°F | 88°F | 70°F | 1.0" |
| October | 51°F | 83°F | 64°F | 3.9" |
| November | 46°F | 78°F | 59°F | 19.8" |
| December | 39°F | 66°F | 51°F | 4.9" |
| Index | Highland | California | National |
| Air quality index | 89 | 55 | 42 |
| Pollution index | 31,575,300 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 42 |
| Days with moderate air quality | 178 |
| Days w/ poor A.Q. for sensitive groups | 79 |
| Days with unhealthy air quality | 58 |
| Pollutant | Total |
| Arsenic | 0.110% |
| Benzene | 0.260% |
| Carbon Tetrachloride | 0.020% |
| Lead | 0.350% |
| Mercury | 0.280% |
| City | Population | Air Quality Index | National Avg. |
| Bloomington, CA | 21,907 | 89 | 78.0% |
| Grand Terrace, CA | 12,559 | 89 | 78.0% |
| Mentone, CA | 10,141 | 89 | 78.0% |
| Riverside, CA | 327,569 | 89 | 78.0% |
| Muscoy, CA | 11,546 | 89 | 78.0% |
| Highland, CA | 55,339 | 89 | 78.0% |
| City | Population | Air Quality Index | National Avg. |
| Hacienda Heights, CA | 55,386 | 72 | 44.0% |
| Kettering, OH | 55,271 | 47 | 6.0% |
| Blue Springs, MO | 55,415 | 47 | 6.0% |
| Oak Lawn, IL | 55,432 | 55 | 10.0% |
| Carson City, NV | 55,244 | 41 | 18.0% |
| Highland, CA | 55,339 | 89 | 78.0% |
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