Generally, I would guess that Bellingham sees its first snow sometime in November, but it all depends.
Snow is most likely to occur though......between November and late February-early March.
MOST of the time, whatever snow occurs.....is generally, light in accumulation with locally higher amounts with elevation change to the east of town. Sometimes it snows and then turns to rain soon after.
Other times, enough cold air comes down the Fraser River Valley in lower BC, Canada and floods on into northern and central Whatcom county. It CAN get brutally cold when THIS meteorological event sets up and if enough moisture comes in off of the Pacific....into this cold airmass.....WATCH OUT!

It CAN DUMP a LOT of snow.....and all the way down to sea level!! When this occurs.....just plan on the roads being a MESS for a while, be grateful if you don't lose power and hope that a rapid warmup is coming soon. Sadly though, if any warmup is TOO rapid and with a "Pineapple Express" jet stream coming all the way up from Hawaii....it'll be a much warmer and much wetter airmass and after a big snow.....this scenario often spells real trouble from river flooding all over western WA. The Nooksack River in Whatcom County.....IS one river that does flood in parts of the county......around Ferndale (the Silver Reef Casino area) and around Lynden, especially. Near Deming too.
Also....when THIS amount of snow or ice grips the region......it can be VERY difficult to traverse ANY hilly areas, including the entire Sudden Valley area which has a LOT of homes on hilly streets with MANY steep driveways. Just something to think about.