| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 48°F | 67°F | 56°F | 1.8" |
| February | 49°F | 66°F | 56°F | 2.0" |
| March | 51°F | 67°F | 58°F | 1.1" |
| April | 54°F | 68°F | 60°F | 0.7" |
| May | 58°F | 69°F | 63°F | 0.4" |
| June | 61°F | 71°F | 65°F | 0.0" |
| July | 65°F | 75°F | 69°F | 0.1" |
| August | 66°F | 76°F | 70°F | 0.1" |
| September | 64°F | 77°F | 70°F | 0.1" |
| October | 59°F | 75°F | 67°F | 0.5" |
| November | 53°F | 71°F | 61°F | 1.0" |
| December | 48°F | 66°F | 56°F | 2.7" |
| Index | Lake San Marcos | California | National |
| Air quality index | 64 | 55 | 42 |
| Pollution index | 45,820,500 | 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 | 1.130% |
| Benzene | 0.410% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.600% |
| Mercury | 0.080% |
| City | Population | Air Quality Index | National Avg. |
| Poway, CA | 49,780 | 64 | 28.0% |
| Hidden Meadows, CA | 3,675 | 64 | 28.0% |
| Encinitas, CA | 62,967 | 64 | 28.0% |
| Rancho Santa Fe, CA | 2,657 | 64 | 28.0% |
| Bonsall, CA | 4,194 | 64 | 28.0% |
| Lake San Marcos, CA | 3,957 | 64 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Southgate, KY | 3,957 | 54 | 8.0% |
| Level Green, PA | 3,957 | 56 | 12.0% |
| Grand Mound, WA | 3,957 | 20 | 60.0% |
| Ashland, MO | 3,956 | 38 | 24.0% |
| Weaverville, NC | 3,956 | 44 | 12.0% |
| Lake San Marcos, CA | 3,957 | 64 | 28.0% |
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