| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 8°F | 25°F | 16°F | 0.4" |
| February | 11°F | 29°F | 19°F | 0.7" |
| March | 24°F | 42°F | 32°F | 1.7" |
| April | 35°F | 57°F | 45°F | 2.7" |
| May | 46°F | 70°F | 57°F | 4.4" |
| June | 57°F | 79°F | 67°F | 6.6" |
| July | 62°F | 84°F | 73°F | 6.9" |
| August | 59°F | 80°F | 69°F | 7.0" |
| September | 50°F | 73°F | 61°F | 8.2" |
| October | 38°F | 59°F | 47°F | 5.0" |
| November | 25°F | 46°F | 34°F | 1.5" |
| December | 11°F | 28°F | 18°F | 1.6" |
| Index | Sinai | South Dakota | National |
| Air quality index | 42 | 36 | 42 |
| Pollution index | 1,169,770 | 345,623 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 284 |
| Days with moderate air quality | 76 |
| Days w/ poor A.Q. for sensitive groups | 5 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Bruce, SD | 259 | 42 | 16.0% |
| Oldham, SD | 131 | 42 | 16.0% |
| Brookings, SD | 24,479 | 42 | 16.0% |
| Nunda, SD | 50 | 42 | 16.0% |
| Arlington, SD | 1,007 | 42 | 16.0% |
| Sinai, SD | 166 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Movico, AL | 166 | 42 | 16.0% |
| Sierraville, CA | 166 | 44 | 12.0% |
| Wawona, CA | 166 | 50 | = 100 |
| Bethune, CO | 166 | 45 | 10.0% |
| Crook, CO | 166 | 19 | 62.0% |
| Sinai, SD | 166 | 42 | 16.0% |
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