December weather in Mercer Island, WA
The average temperature in Mercer Island in December is 42.0°F (36.2°F–47.8°F). Average precipitation: 5.49 inches.
December is a winter month in Mercer Island, and is cooler than the annual average of 53.8°F. Daily temperatures swing about 11.6°F between overnight low and afternoon high. Expect about 18 days with precipitation. Daylight averages about 8h 15m. For travel, December is a wet month.
Avg High
47.8°F
Avg Low
36.2°F
Precipitation
5.49 in
Daylight
8h 15m
December records in Mercer Island
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| December 1 | 59.0°F (1958) | 25.2°F (2014) | 0.90 in (2001) |
| December 2 | 60.1°F (1958) | 24.3°F (2022) | 1.55 in (2007) |
| December 3 | 60.1°F (2007) | 28.2°F (2009) | 3.96 in (2007) |
| December 4 | 57.0°F (1949) | 26.1°F (2005) | 0.68 in (2023) |
| December 5 | 63.0°F (2015) | 22.1°F (2013) | 1.23 in (2023) |
| December 6 | 59.0°F (2015) | 19.9°F (1956) | 0.59 in (1950) |
| December 7 | 57.9°F (1962) | 18.1°F (2013) | 1.07 in (2015) |
| December 8 | 63.0°F (2015) | 17.2°F (2013) | 1.51 in (2015) |
| December 9 | 63.0°F (2014) | 16.2°F (2009) | 1.36 in (1956) |
| December 10 | 69.1°F (2014) | 14.2°F (2009) | 0.64 in (1958) |
| December 11 | 60.1°F (2014) | 18.1°F (2009) | 1.48 in (2010) |
| December 12 | 61.0°F (1952) | 20.1°F (2009) | 2.21 in (2010) |
| December 13 | 62.1°F (1952) | 28.9°F (1955) | 1.62 in (2001) |
| December 14 | 61.0°F (2002) | 20.1°F (2008) | 1.92 in (2006) |
| December 15 | 59.0°F (2025) | 21.9°F (1964) | 1.28 in (1959) |
| December 16 | 57.0°F (2025) | 10.9°F (1964) | 1.23 in (1961) |
| December 17 | 55.9°F (2024) | 12.0°F (1964) | 0.82 in (2015) |
| December 18 | 57.0°F (1959) | 21.0°F (1964) | 0.89 in (1951) |
| December 19 | 57.0°F (1950) | 1.2°F (2012) | 1.14 in (2017) |
| December 20 | 59.0°F (2014) | 1.2°F (2012) | 1.60 in (1955) |
| December 21 | 57.9°F (2014) | 18.0°F (1998) | 1.78 in (2020) |
| December 22 | 57.0°F (1950) | 15.1°F (1998) | 1.17 in (1964) |
| December 23 | 61.0°F (1950) | 18.0°F (1998) | 1.27 in (1949) |
| December 24 | 60.1°F (2005) | 18.0°F (1948) | 1.00 in (2022) |
| December 25 | 57.9°F (2005) | 24.1°F (1962) | 0.91 in (1957) |
| December 26 | 55.9°F (2022) | 22.1°F (2021) | 1.44 in (2006) |
| December 27 | 55.0°F (2022) | 17.2°F (2021) | 0.91 in (1949) |
| December 28 | 55.0°F (2023) | 23.2°F (2021) | 0.61 in (1952) |
| December 29 | 62.1°F (2023) | 23.2°F (2021) | 1.37 in (2017) |
| December 30 | 60.1°F (1958) | 24.1°F (2003) | 0.82 in (1962) |
| December 31 | 59.0°F (1963) | 17.1°F (1951) | 0.82 in (1963) |