| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 38°F | 29°F | 4.4" |
| February | 21°F | 40°F | 30°F | 3.5" |
| March | 30°F | 52°F | 40°F | 5.0" |
| April | 40°F | 64°F | 51°F | 4.5" |
| May | 49°F | 72°F | 60°F | 6.0" |
| June | 57°F | 79°F | 68°F | 8.6" |
| July | 61°F | 82°F | 71°F | 9.8" |
| August | 59°F | 81°F | 69°F | 6.1" |
| September | 53°F | 76°F | 63°F | 6.0" |
| October | 42°F | 64°F | 52°F | 4.2" |
| November | 32°F | 54°F | 42°F | 3.7" |
| December | 26°F | 43°F | 34°F | 4.5" |
| Index | Washington | Pennsylvania | National |
| Air quality index | 56 | 45 | 42 |
| Pollution index | 2,548,030 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 129 |
| Days with moderate air quality | 220 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 4 |
| Pollutant | Total |
| Arsenic | 0.220% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.050% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Deemston, PA | 702 | 36 | 28.0% |
| Fredericktown, PA | 200 | 36 | 28.0% |
| Marianna, PA | 531 | 36 | 28.0% |
| Clarksville, PA | 199 | 36 | 28.0% |
| Millsboro, PA | 503 | 36 | 28.0% |
| Washington, PA | 13,404 | 56 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Moss Point, MS | 13,396 | 32 | 36.0% |
| Beaufort, SC | 13,417 | 29 | 42.0% |
| Dardenne Prairie, MO | 13,385 | 54 | 8.0% |
| Brainerd, MN | 13,423 | 29 | 42.0% |
| New Providence, NJ | 13,382 | 51 | 2.0% |
| Washington, PA | 13,404 | 56 | 12.0% |
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