| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 32°F | 24°F | 1.5" |
| February | 19°F | 38°F | 28°F | 1.0" |
| March | 26°F | 48°F | 36°F | 1.3" |
| April | 31°F | 57°F | 43°F | 1.4" |
| May | 38°F | 68°F | 52°F | 1.7" |
| June | 44°F | 74°F | 59°F | 3.1" |
| July | 48°F | 86°F | 68°F | 1.0" |
| August | 46°F | 84°F | 65°F | 0.8" |
| September | 39°F | 73°F | 55°F | 1.2" |
| October | 31°F | 57°F | 43°F | 1.5" |
| November | 25°F | 42°F | 33°F | 1.4" |
| December | 16°F | 30°F | 23°F | 1.9" |
| Index | Eureka | Montana | National |
| Air quality index | 37 | 34 | 42 |
| Pollution index | 968,253 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 302 |
| Days with moderate air quality | 62 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Midvale, MT | 440 | 37 | 26.0% |
| West Kootenai, MT | 84 | 37 | 26.0% |
| Rexford, MT | 58 | 37 | 26.0% |
| Fortine, MT | 435 | 37 | 26.0% |
| Stryker, MT | 22 | 37 | 26.0% |
| Eureka, MT | 1,517 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Cypress Quarters, FL | 1,517 | 36 | 28.0% |
| Oronoco, MN | 1,517 | 36 | 28.0% |
| Hayden, AL | 1,516 | 53 | 6.0% |
| Del Rey Oaks, CA | 1,518 | 37 | 26.0% |
| Osborne, KS | 1,518 | 19 | 62.0% |
| Eureka, MT | 1,517 | 37 | 26.0% |
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