| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 37°F | 26°F | 0.8" |
| February | 18°F | 40°F | 28°F | 1.1" |
| March | 27°F | 52°F | 39°F | 0.8" |
| April | 33°F | 60°F | 46°F | 2.6" |
| May | 38°F | 64°F | 51°F | 3.6" |
| June | 50°F | 78°F | 65°F | 4.5" |
| July | 55°F | 86°F | 71°F | 4.0" |
| August | 53°F | 84°F | 69°F | 1.6" |
| September | 46°F | 73°F | 60°F | 3.4" |
| October | 37°F | 62°F | 49°F | 3.5" |
| November | 24°F | 47°F | 35°F | 1.6" |
| December | 14°F | 34°F | 24°F | 1.1" |
| Index | Hays | Montana | National |
| Air quality index | 21 | 34 | 42 |
| Pollution index | 232,374 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 350 |
| Days with moderate air quality | 12 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| 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. |
| Zortman, MT | 33 | 21 | 58.0% |
| Lodge Pole, MT | 344 | 21 | 58.0% |
| Hays, MT | 947 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| Susan Moore, AL | 947 | 43 | 14.0% |
| Otisville, MI | 947 | 38 | 24.0% |
| Grantwood Village, MO | 947 | 54 | 8.0% |
| Waverly, MO | 947 | 47 | 6.0% |
| Newark Valley, NY | 947 | 34 | 32.0% |
| Hays, MT | 947 | 21 | 58.0% |
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