| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 32°F | 47°F | 38°F | 4.1" |
| February | 33°F | 53°F | 42°F | 3.0" |
| March | 38°F | 60°F | 48°F | 4.8" |
| April | 39°F | 61°F | 50°F | 2.9" |
| May | 45°F | 70°F | 57°F | 4.8" |
| June | 48°F | 72°F | 59°F | 2.1" |
| July | 53°F | 83°F | 68°F | 1.3" |
| August | 51°F | 84°F | 67°F | 1.2" |
| September | 44°F | 75°F | 59°F | 2.8" |
| October | 42°F | 61°F | 50°F | 3.8" |
| November | 33°F | 52°F | 42°F | 7.5" |
| December | 33°F | 45°F | 39°F | 11.3" |
| Index | Tigard | Oregon | National |
| Air quality index | 38 | 32 | 42 |
| Pollution index | 11,541,100 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 285 |
| Days with moderate air quality | 77 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.020% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| St. Paul, OR | 396 | 32 | 36.0% |
| Dayton, OR | 2,726 | 32 | 36.0% |
| Donald, OR | 1,465 | 32 | 36.0% |
| Dundee, OR | 3,296 | 32 | 36.0% |
| Cornelius, OR | 12,767 | 38 | 24.0% |
| Tigard, OR | 54,149 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Grapevine, TX | 54,151 | 51 | 2.0% |
| Mount Prospect, IL | 54,165 | 55 | 10.0% |
| Colton, CA | 54,215 | 89 | 78.0% |
| North Bay, ON | 53,968 | n/a | |
| Rocky Mount, NC | 54,330 | 36 | 28.0% |
| Tigard, OR | 54,149 | 38 | 24.0% |
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