| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 43°F | 66°F | 54°F | 11.6" |
| February | 47°F | 67°F | 56°F | 9.6" |
| March | 48°F | 74°F | 60°F | 2.1" |
| April | 50°F | 76°F | 61°F | 4.1" |
| May | 55°F | 81°F | 66°F | 4.8" |
| June | 58°F | 86°F | 70°F | 0.1" |
| July | 65°F | 94°F | 78°F | 0.2" |
| August | 65°F | 95°F | 78°F | 2.3" |
| September | 60°F | 88°F | 72°F | 2.1" |
| October | 57°F | 82°F | 67°F | 4.3" |
| November | 50°F | 77°F | 62°F | 7.7" |
| December | 43°F | 67°F | 55°F | 3.3" |
| Index | Rialto | 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. |
| Fontana, CA | 212,704 | 89 | 78.0% |
| San Bernardino, CA | 216,784 | 89 | 78.0% |
| Grand Terrace, CA | 12,559 | 89 | 78.0% |
| Moreno Valley, CA | 208,751 | 89 | 78.0% |
| Norco, CA | 27,021 | 89 | 78.0% |
| Rialto, CA | 103,549 | 89 | 78.0% |
| City | Population | Air Quality Index | National Avg. |
| San Mateo, CA | 103,619 | 43 | 14.0% |
| Burbank, CA | 103,411 | 72 | 44.0% |
| El Cajon, CA | 103,249 | 64 | 28.0% |
| Allen, TX | 104,040 | 51 | 2.0% |
| Las Cruces, NM | 102,950 | 51 | 2.0% |
| Rialto, CA | 103,549 | 89 | 78.0% |
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