| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 2°F | 21°F | 12°F | 1.0" |
| February | 4°F | 23°F | 13°F | 0.8" |
| March | 15°F | 36°F | 24°F | 1.9" |
| April | 26°F | 50°F | 37°F | 2.2" |
| May | 39°F | 67°F | 53°F | 6.2" |
| June | 50°F | 76°F | 63°F | 8.2" |
| July | 55°F | 79°F | 66°F | 3.4" |
| August | 52°F | 81°F | 65°F | 2.0" |
| September | 46°F | 72°F | 57°F | 4.5" |
| October | 32°F | 55°F | 42°F | 3.4" |
| November | 17°F | 37°F | 26°F | 1.3" |
| December | 3°F | 21°F | 12°F | 0.5" |
| Index | Portal | North Dakota | National |
| Air quality index | 34 | 35 | 42 |
| Pollution index | 173,888 | 1,038,665 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 309 |
| Days with moderate air quality | 53 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 0 |
| 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. |
| Bowbells, ND | 299 | 34 | 32.0% |
| Lignite, ND | 157 | 34 | 32.0% |
| Columbus, ND | 74 | 34 | 32.0% |
| Flaxton, ND | 112 | 34 | 32.0% |
| Larson, ND | 0 | 34 | 32.0% |
| Portal, ND | 132 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Yellow Bluff, AL | 132 | 52 | 4.0% |
| Vallecito, CA | 132 | 39 | 22.0% |
| Otter Creek, FL | 132 | 35 | 30.0% |
| Blockton, IA | 132 | 43 | 14.0% |
| Geneva, IA | 132 | 15 | 70.0% |
| Portal, ND | 132 | 34 | 32.0% |
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