| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 44°F | 35°F | 6.3" |
| February | 28°F | 46°F | 36°F | 4.5" |
| March | 35°F | 55°F | 44°F | 6.6" |
| April | 45°F | 66°F | 55°F | 6.3" |
| May | 55°F | 75°F | 64°F | 5.8" |
| June | 64°F | 83°F | 73°F | 8.1" |
| July | 69°F | 87°F | 78°F | 10.2" |
| August | 67°F | 85°F | 76°F | 9.2" |
| September | 61°F | 79°F | 69°F | 9.7" |
| October | 50°F | 69°F | 59°F | 9.2" |
| November | 39°F | 58°F | 48°F | 5.9" |
| December | 33°F | 50°F | 41°F | 7.5" |
| Index | Hartly | Delaware | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 3,193,180 | 7,274,307 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 293 |
| Days with moderate air quality | 72 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Camden, DE | 3,529 | 42 | 16.0% |
| Smyrna, DE | 11,694 | 42 | 16.0% |
| Wyoming, DE | 1,596 | 42 | 16.0% |
| Goldsboro, MD | 215 | 42 | 16.0% |
| Millington, MD | 610 | 42 | 16.0% |
| Hartly, DE | 167 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Lidderdale, IA | 167 | 37 | 26.0% |
| Sims, IL | 167 | 43 | 14.0% |
| Salvisa, KY | 167 | 42 | 16.0% |
| Burkittsville, MD | 167 | 40 | 20.0% |
| Marietta, MN | 167 | 25 | 50.0% |
| Hartly, DE | 167 | 42 | 16.0% |
Here are the best places to live in Delaware
Check out the 10 most dangerous cities in Delaware
Check out the 10 safest cities in Delaware
Most Dangerous States In The US