| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 34°F | 65°F | 49°F | 10.5" |
| February | 39°F | 65°F | 51°F | 8.0" |
| March | 41°F | 70°F | 54°F | 3.0" |
| April | 41°F | 72°F | 55°F | 2.9" |
| May | 48°F | 77°F | 61°F | 0.9" |
| June | 49°F | 83°F | 65°F | 0.2" |
| July | 56°F | 91°F | 72°F | 1.5" |
| August | 58°F | 92°F | 73°F | 0.5" |
| September | 50°F | 86°F | 67°F | 0.4" |
| October | 47°F | 79°F | 62°F | 2.1" |
| November | 42°F | 75°F | 57°F | 3.5" |
| December | 34°F | 67°F | 50°F | 2.5" |
| Index | Julian | 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. |
| Descanso, CA | 1,398 | 64 | 28.0% |
| Mount Laguna, CA | 102 | 64 | 28.0% |
| San Diego Country Estates, CA | 9,752 | 64 | 28.0% |
| Borrego Springs, CA | 1,864 | 64 | 28.0% |
| Julian, CA | 1,318 | 64 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| La Harpe, IL | 1,318 | 29 | 42.0% |
| Mulberry, IN | 1,319 | 42 | 16.0% |
| Coal Run Village, KY | 1,319 | 42 | 16.0% |
| Red Lake Falls, MN | 1,319 | 33 | 34.0% |
| Winthrop, MN | 1,317 | 46 | 8.0% |
| Julian, CA | 1,318 | 64 | 28.0% |
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