December in Tri-Cities averages a daily high of 4.9°C with nights around -2.6°C. Expect roughly 10.5 wet days totalling 26.3mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Tri-Cities is April–May.
Based on PASCO TRI CITIES AIRPORT, WA US (6.6km), 1995–2024. 27 years of December data.