30-year climate normals
Washington County Climate and Weather Averages
Hottest month — August
82.2°average daily high. The coldest month is January, averaging a low of 32.6°F.
Washington County gets 46.72" of precipitation a year and 2.7" of snow, and 50% of it falls in Nov, Dec, Jan.
Temperature through the year
Each bar spans the average daily low to the average daily high for that month.
| Month | Avg high | Avg low | Precip | Snow |
|---|---|---|---|---|
| January | 45.0° | 32.6° | 7.19" | 0.6" |
| February | 49.4° | 33.1° | 5.76" | 0.6" |
| March | 54.6° | 35.9° | 5.03" | 0.0" |
| April | 60.1° | 39.2° | 3.33" | 0.0" |
| May | 68.1° | 45.3° | 2.19" | 0.0" |
| June | 73.1° | 49.7° | 1.40" | 0.0" |
| July | 81.4° | 53.8° | 0.32" | 0.0" |
| August | 82.2° | 53.5° | 0.51" | 0.0" |
| September | 76.1° | 48.7° | 1.34" | 0.0" |
| October | 63.3° | 41.6° | 3.70" | 0.2" |
| November | 50.9° | 36.3° | 7.23" | 0.0" |
| December | 44.0° | 32.8° | 8.72" | 1.3" |
Rainfall by month
Washington County has a distinct wet season. 50% of the year's precipitation arrives in Nov, Dec, Jan.
What this climate costs you
Degree days measure how hard a building has to work to stay comfortable. They are the reason two identical houses have very different power bills, and they are the link between the weather here and what you pay every month.
These are rough planning figures from degree days and the state electricity price, not a bill estimate. House size, insulation and fuel type move them a lot. See the full cost of owning a home in Washington County, where electricity is one line of eight.
Common questions
What is the weather like in Washington County?
Washington County averages a high of 82.2°F in August and a low of 32.6°F in January. Annual precipitation is 46.72 inches, including 2.7 inches of snow.
When is the rainy season in Washington County?
The wettest stretch is Nov, Dec, Jan, which accounts for 50% of the year's precipitation. That is a pronounced wet season rather than rain spread evenly through the year.
How hot does it get in Washington County?
The average daily high in August, the hottest month, is 82.2°F. That drives 347 cooling degree days a year, which is what your air conditioning has to work against.
Does it snow in Washington County?
Yes. Washington County averages 2.7 inches of snow a year.
Sources
- Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station FOREST GROVE, OR US (USC00352997), 2 miles from the county centroid.
- Heating and cooling degree days — NOAA, same station and period.
- Electricity price — US Energy Information Administration, Electric Power Monthly Table 5.6.A, Oregon residential average.
- Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.