| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 29°F | 20°F | 0.6" |
| February | 13°F | 32°F | 22°F | 0.8" |
| March | 28°F | 48°F | 37°F | 1.7" |
| April | 39°F | 62°F | 49°F | 4.8" |
| May | 50°F | 73°F | 61°F | 5.8" |
| June | 60°F | 82°F | 71°F | 5.1" |
| July | 63°F | 84°F | 74°F | 4.0" |
| August | 61°F | 82°F | 71°F | 4.9" |
| September | 52°F | 77°F | 64°F | 3.9" |
| October | 41°F | 63°F | 51°F | 2.9" |
| November | 29°F | 49°F | 38°F | 1.5" |
| December | 16°F | 33°F | 24°F | 1.4" |
| Index | Garwin | Iowa | National |
| Air quality index | 39 | 39 | 50 |
| Pollution index | 416,114 | 1,643,836 | 5,066,862 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 286 |
| Days with moderate air quality | 77 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.004% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City, State | Population | Air Quality Index | National Avg. |
| Gilman, IA | 598 | 37 | 26% |
| Laurel, IA | 358 | 37 | 26% |
| Ferguson, IA | 137 | 37 | 26% |
| Haverhill, IA | 169 | 37 | 26% |
| Marshalltown, IA | 27,637 | 37 | 26% |
| Garwin, IA | 503 | 39 | 22% |
| City, State | Population | Air Quality Index | National Avg. |
| Malone, WA | 503 | 30 | 40% |
| Jacksonboro, SC | 503 | 29 | 42% |
| Fillmore, NY | 503 | 39 | 22% |
| Toksook Bay, AK | 503 | 31 | 38% |
| Mooresboro, NC | 503 | 36 | 28% |
| Garwin, IA | 503 | 39 | 22% |
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