| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | -1°F | 18°F | 7°F | 1.0" |
| February | 2°F | 19°F | 10°F | 0.4" |
| March | 18°F | 37°F | 26°F | 1.8" |
| April | 33°F | 58°F | 44°F | 2.3" |
| May | 47°F | 68°F | 57°F | 8.9" |
| June | 59°F | 77°F | 68°F | 7.4" |
| July | 61°F | 82°F | 72°F | 3.8" |
| August | 57°F | 79°F | 68°F | 6.4" |
| September | 48°F | 73°F | 60°F | 2.5" |
| October | 38°F | 57°F | 47°F | 6.6" |
| November | 23°F | 39°F | 30°F | 2.3" |
| December | 6°F | 21°F | 14°F | 1.2" |
| Index | Portland | North Dakota | National |
| Air quality index | 33 | 35 | 42 |
| Pollution index | 151,183 | 1,038,665 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 327 |
| Days with moderate air quality | 34 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.002% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Clifford, ND | 37 | 33 | 34.0% |
| Hatton, ND | 783 | 33 | 34.0% |
| Hillsboro, ND | 1,627 | 33 | 34.0% |
| Mayville, ND | 1,892 | 33 | 34.0% |
| Buxton, ND | 431 | 33 | 34.0% |
| Portland, ND | 666 | 33 | 34.0% |
| City | Population | Air Quality Index | National Avg. |
| Western Grove, AR | 666 | 36 | 28.0% |
| Sky Valley, GA | 666 | 41 | 18.0% |
| Pilot Grove, MO | 666 | 38 | 24.0% |
| Mount Victory, OH | 666 | 39 | 22.0% |
| Boykins, VA | 666 | 36 | 28.0% |
| Portland, ND | 666 | 33 | 34.0% |
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