| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 7°F | 26°F | 15°F | 0.8" |
| February | 10°F | 27°F | 17°F | 1.4" |
| March | 24°F | 44°F | 32°F | 2.6" |
| April | 35°F | 58°F | 45°F | 6.4" |
| May | 49°F | 71°F | 58°F | 6.6" |
| June | 60°F | 80°F | 69°F | 8.9" |
| July | 62°F | 85°F | 73°F | 5.8" |
| August | 58°F | 82°F | 68°F | 7.5" |
| September | 53°F | 78°F | 63°F | 5.3" |
| October | 40°F | 63°F | 50°F | 6.0" |
| November | 26°F | 46°F | 34°F | 2.2" |
| December | 11°F | 26°F | 18°F | 1.2" |
| Index | Ortley | South Dakota | National |
| Air quality index | 25 | 36 | 42 |
| Pollution index | 267,939 | 345,623 | 2,726,193 |
| Measurement | Total |
| Days measured | 361 |
| Days with good air quality | 325 |
| Days with moderate air quality | 36 |
| 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 | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Marvin, SD | 18 | 25 | 50.0% |
| Peever, SD | 186 | 25 | 50.0% |
| Roslyn, SD | 221 | 25 | 50.0% |
| Grenville, SD | 71 | 25 | 50.0% |
| Summit, SD | 339 | 25 | 50.0% |
| Ortley, SD | 58 | 25 | 50.0% |
| City | Population | Air Quality Index | National Avg. |
| Ventana, AZ | 58 | 74 | 48.0% |
| Carrick, CA | 58 | 42 | 16.0% |
| Jeisyville, IL | 58 | 40 | 20.0% |
| Bethany, IN | 58 | 54 | 8.0% |
| Soldier, KS | 58 | 41 | 18.0% |
| Ortley, SD | 58 | 25 | 50.0% |
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