| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 29°F | 20°F | 0.8" |
| February | 14°F | 32°F | 23°F | 1.0" |
| March | 28°F | 48°F | 37°F | 2.1" |
| April | 39°F | 63°F | 50°F | 4.6" |
| May | 50°F | 73°F | 61°F | 3.9" |
| June | 60°F | 81°F | 70°F | 7.0" |
| July | 63°F | 84°F | 73°F | 4.8" |
| August | 61°F | 82°F | 71°F | 4.7" |
| September | 53°F | 76°F | 64°F | 4.0" |
| October | 42°F | 63°F | 52°F | 3.1" |
| November | 29°F | 49°F | 38°F | 2.1" |
| December | 17°F | 33°F | 25°F | 1.9" |
| Index | Williamsburg | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 684,464 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 278 |
| Days with moderate air quality | 86 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| North English, IA | 957 | 35 | 30.0% |
| Parnell, IA | 210 | 35 | 30.0% |
| Oxford, IA | 707 | 35 | 30.0% |
| Keswick, IA | 295 | 35 | 30.0% |
| Wellman, IA | 1,428 | 35 | 30.0% |
| Williamsburg, IA | 3,152 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Mountain Home AFB, ID | 3,151 | 36 | 28.0% |
| Ocean Grove, NJ | 3,151 | 51 | 2.0% |
| Rankin Inlet, NU | 3,151 | n/a | |
| New Baden, IL | 3,150 | 54 | 8.0% |
| Stonybrook, PA | 3,150 | 41 | 18.0% |
| Williamsburg, IA | 3,152 | 35 | 30.0% |
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