| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 58°F | 46°F | 5.2" |
| February | 34°F | 59°F | 45°F | 7.8" |
| March | 42°F | 69°F | 54°F | 8.8" |
| April | 47°F | 74°F | 60°F | 6.3" |
| May | 55°F | 81°F | 67°F | 4.7" |
| June | 66°F | 87°F | 75°F | 8.0" |
| July | 70°F | 90°F | 78°F | 2.9" |
| August | 71°F | 94°F | 81°F | 4.4" |
| September | 63°F | 89°F | 75°F | 0.7" |
| October | 54°F | 78°F | 64°F | 6.1" |
| November | 40°F | 68°F | 52°F | 3.4" |
| December | 35°F | 59°F | 46°F | 8.1" |
| Index | McCormick | South Carolina | National |
| Air quality index | 47 | 37 | 42 |
| Pollution index | 1,548,730 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 219 |
| Days with moderate air quality | 144 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Willington, SC | 0 | 31 | 38.0% |
| Bradley, SC | 127 | 31 | 38.0% |
| Promised Land, SC | 555 | 31 | 38.0% |
| Troy, SC | 145 | 31 | 38.0% |
| Mount Carmel, SC | 271 | 31 | 38.0% |
| McCormick, SC | 3,043 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Bishopville, SC | 3,043 | 40 | 20.0% |
| East Gaffney, SC | 3,043 | 36 | 28.0% |
| West Brattleboro, VT | 3,042 | 34 | 32.0% |
| Longtown, OK | 3,044 | 43 | 14.0% |
| Algoma, WI | 3,044 | 36 | 28.0% |
| McCormick, SC | 3,043 | 47 | 6.0% |
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