| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 44°F | 70°F | 56°F | 1.6" |
| February | 45°F | 72°F | 57°F | 1.2" |
| March | 47°F | 75°F | 60°F | 0.7" |
| April | 50°F | 78°F | 63°F | 0.5" |
| May | 55°F | 82°F | 66°F | 0.2" |
| June | 59°F | 89°F | 72°F | 0.0" |
| July | 65°F | 94°F | 77°F | 0.2" |
| August | 65°F | 95°F | 78°F | 0.1" |
| September | 63°F | 94°F | 76°F | 0.2" |
| October | 56°F | 85°F | 69°F | 0.2" |
| November | 49°F | 77°F | 62°F | 0.5" |
| December | 44°F | 69°F | 55°F | 1.9" |
| Index | Lake Mathews | California | National |
| Air quality index | 89 | 55 | 42 |
| Pollution index | 22,790,900 | 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 | 0.060% |
| Benzene | 0.190% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.220% |
| Mercury | 0.230% |
| City | Population | Air Quality Index | National Avg. |
| Grand Terrace, CA | 12,559 | 89 | 78.0% |
| Moreno Valley, CA | 208,751 | 89 | 78.0% |
| Coronita, CA | 3,968 | 89 | 78.0% |
| Rancho Santa Margarita, CA | 48,280 | 89 | 78.0% |
| Lakeland Village, CA | 12,362 | 89 | 78.0% |
| Lake Mathews, CA | 7,389 | 89 | 78.0% |
| City | Population | Air Quality Index | National Avg. |
| Heathcote, NJ | 7,389 | 41 | 18.0% |
| Mount Ivy, NY | 7,390 | 36 | 28.0% |
| Mentor-on-the-Lake, OH | 7,391 | 50 | = 100 |
| Saint-Philippe, QC | 7,384 | n/a | |
| Hiawatha, IA | 7,395 | 39 | 22.0% |
| Lake Mathews, CA | 7,389 | 89 | 78.0% |
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