| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 62°F | 49°F | 2.2" |
| February | 34°F | 64°F | 49°F | 2.2" |
| March | 36°F | 68°F | 51°F | 1.3" |
| April | 38°F | 72°F | 54°F | 0.7" |
| May | 42°F | 77°F | 59°F | 0.4" |
| June | 46°F | 88°F | 68°F | 0.1" |
| July | 55°F | 92°F | 74°F | 0.2" |
| August | 55°F | 93°F | 74°F | 0.2" |
| September | 52°F | 89°F | 70°F | 0.5" |
| October | 44°F | 79°F | 61°F | 0.6" |
| November | 39°F | 70°F | 54°F | 0.8" |
| December | 35°F | 62°F | 48°F | 2.8" |
| Index | Descanso | California | National |
| Air quality index | 64 | 55 | 42 |
| Pollution index | 162,740 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 87 |
| Days with moderate air quality | 253 |
| Days w/ poor A.Q. for sensitive groups | 23 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.003% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Mount Laguna, CA | 102 | 64 | 28.0% |
| Harbison Canyon, CA | 4,355 | 64 | 28.0% |
| Pine Valley, CA | 1,611 | 64 | 28.0% |
| Ramona, CA | 21,493 | 64 | 28.0% |
| Jamul, CA | 5,776 | 64 | 28.0% |
| Descanso, CA | 1,398 | 64 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Payson, IL | 1,398 | 41 | 18.0% |
| Philo, IL | 1,398 | 42 | 16.0% |
| Brookston, IN | 1,398 | 42 | 16.0% |
| Okarche, OK | 1,398 | 48 | 4.0% |
| Aptos Hills-Larkin Valley, CA | 1,397 | 35 | 30.0% |
| Descanso, CA | 1,398 | 64 | 28.0% |
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