This morning National Weather Service (NWS) Seattle office forecasters issued a Winter Storm Watch for northern Puget Sound lowlands including the northern slopes of the Olympics and western Whatcom County. The statement said to expect snow and powerful northeast winds from Friday morning through Saturday afternoon.
In light of the certainty of a snow event over much of western Washington, there have been plenty of warnings to prepare (stock up on groceries, fill gas tanks, etc.) and attempts at forecasting how much snow to expect. Unfortunately for us in Whatcom County, much of this information comes from Seattle-centric sources and what is expected to happen in Seattle gets applied to all of western Washington.
According to the latest computer weather forecast models, the upcoming snow event appears to hit the Tacoma-Seattle-Everett area with much more snow than it will north of Skagit County. While NWS forecasters say some western Washington regions can expect upwards of a foot or more of snow, western Whatcom County is not likely to get more than 6 inches. More likely, 2 to 3 inches is expected, if that.
The graph below is a representation of several different runs of the US Global Forecast System (GFS) computer weather model’s forecast for snow on Friday and Saturday using Bellingham as the location. Each run incorporates slightly different scenarios in order to determine the most likely forecast based on available data.
According to this graph, the primary run (the blue line) says to expect a total of 0 inches of snow. The highest run says to expect 4 inches and the mean (the black line) is at 1.3 inches.
Looking at the same graph for using Seattle as the location reveals an entirely different scenario.
According to the Seattle area graph, the primary run says to expect a total of 6.5 inches of snow and is also highest run. The mean is at 3.6 inches, more than twice what was forecast for Bellingham.
The GFS forecast model is considered reliable for lowland forecasts (not so much for mountain forecasts) and is one of the commonly used computer forecast modeling systems. Combining its current results with highly regarded European Center for Medium-Range Weather Forecasts (ECMWF) model, the current 3-day snowfall estimates in inches for the Ferndale area and the Seattle area are as follows.
NWS forecasters said this morning that western Whatcom County area is currently expected to receive a total accumulation of 2 to 4 inches of snow Friday and Saturday while the Tacoma-Seattle-Everett area can expect twice that amount.
What western Whatcom County can expect that other areas to the south cannot is high winds due to the Fraser Valley outflow. Outflow winds are cold and dry and can result in lower precipitation (e.g. snow) as a result.
This morning’s Winter Weather Watch statement said to expect northeast wind gusts to 60mph. The winds are expected to pick up late Friday afternoon and continue through Saturday night according to recent computer forecast models runs. These winds are expected to be as strong or stronger as the high winds that caused thousands to lose power for hours during the snow and wind weather event earlier this week.