| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 58°F | 47°F | 2.4" |
| February | 42°F | 64°F | 52°F | 1.9" |
| March | 46°F | 70°F | 57°F | 1.7" |
| April | 49°F | 76°F | 61°F | 1.3" |
| May | 54°F | 85°F | 69°F | 0.4" |
| June | 60°F | 93°F | 76°F | 0.2" |
| July | 64°F | 98°F | 80°F | 0.0" |
| August | 63°F | 96°F | 78°F | 0.0" |
| September | 59°F | 91°F | 74°F | 0.1" |
| October | 52°F | 80°F | 64°F | 0.7" |
| November | 44°F | 68°F | 54°F | 1.1" |
| December | 38°F | 58°F | 47°F | 2.3" |
| Index | Modesto | California | National |
| Air quality index | 49 | 55 | 42 |
| Pollution index | 7,774,440 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 201 |
| Days with moderate air quality | 141 |
| Days w/ poor A.Q. for sensitive groups | 22 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.090% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.050% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Lathrop, CA | 23,863 | 45 | 10.0% |
| Manteca, CA | 81,078 | 45 | 10.0% |
| Delhi, CA | 11,837 | 48 | 4.0% |
| West Modesto, CA | 5,557 | 49 | 2.0% |
| Del Rio, CA | 1,241 | 49 | 2.0% |
| Modesto, CA | 214,485 | 49 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Enterprise, NV | 214,591 | 54 | 8.0% |
| Richmond Hill, ON | 215,407 | n/a | |
| Des Moines, IA | 215,408 | 39 | 22.0% |
| Tacoma, WA | 215,766 | 18 | 64.0% |
| Fontana, CA | 212,704 | 89 | 78.0% |
| Modesto, CA | 214,485 | 49 | 2.0% |
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