| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 44°F | 63°F | 53°F | 11.1" |
| February | 47°F | 66°F | 55°F | 4.3" |
| March | 53°F | 73°F | 62°F | 6.1" |
| April | 60°F | 79°F | 69°F | 7.2" |
| May | 66°F | 85°F | 75°F | 20.3" |
| June | 73°F | 90°F | 81°F | 8.9" |
| July | 75°F | 91°F | 82°F | 10.1" |
| August | 76°F | 92°F | 83°F | 3.4" |
| September | 71°F | 89°F | 79°F | 17.1" |
| October | 60°F | 81°F | 69°F | 4.7" |
| November | 51°F | 72°F | 61°F | 5.6" |
| December | 47°F | 65°F | 54°F | 6.6" |
| Index | Welsh | Louisiana | National |
| Air quality index | 45 | 106 | 42 |
| Pollution index | 907,803 | 2,526,475 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 239 |
| Days with moderate air quality | 126 |
| 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 | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Mermentau, LA | 616 | 41 | 18.0% |
| Jennings, LA | 9,874 | 45 | 10.0% |
| Roanoke, LA | 550 | 45 | 10.0% |
| Lacassine, LA | 57 | 45 | 10.0% |
| Fenton, LA | 264 | 45 | 10.0% |
| Welsh, LA | 3,209 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Iowa, LA | 3,209 | 45 | 10.0% |
| Warrensburg, NY | 3,209 | 36 | 28.0% |
| McGovern, PA | 3,209 | 56 | 12.0% |
| Buzzards Bay, MA | 3,208 | 36 | 28.0% |
| Jackson, MN | 3,208 | 32 | 36.0% |
| Welsh, LA | 3,209 | 45 | 10.0% |
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