December in Sammamish averages a daily high of 8.1°C with nights around 2.9°C. Expect roughly 19.9 wet days totalling 147.1mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Sammamish is July–August.
Based on SEATTLE SAND POINT WEATHER FORECAST OFFICE, WA US (14km), 1995–2024. 30 years of December data.