Potpourri of weather warnings for mountain snow, freezing rain and river flooding
SEATTLE -- Mother Nature's got a final one-two punch of storms to finish off its 2017, with freezing rain concerns both up north and in the passes, heavy mountain snows in the higher elevations, and then potential for minor river flooding on mountain-fed rivers.
The first storm was making its way through the region on Thursday. There is still enough lingering arctic air leaking out of the Fraser River Valley in Whatcom County that freezing rain remains a concern. A Winter Storm Warning remains in effect until 4 p.m for western Whatcom County away from the water. Bellingham and Ferndale have already scoured out the cold air and have switched to rain, but areas further inland like Sumas and Lynden may continue to get freezing rain into the early evening hours.
Up in the mountain, it's a mix-mash of freezing rain and heavy snow as warmer air intrudes on the cooler air mass hanging around. A Winter Weather Advisory is in effect for the North and Central Cascades until 6 a.m. Friday for areas above 2,000 feet, when it then upgrades to a Winter Storm Warning through 10 p.m. Friday for areas above 3,000 feet.
While the incoming storms are sweeping in some warmer air off the ocean, it's also drawing in colder air entrenched in Eastern Washington back west through the mountain pass gaps. This is a classic recipe for freezing rain as the warmer air melts the snow aloft, then the rain drops fall into a sub-freezing layer near the roadway and freezes on impact. The potential for freezing rain is there Thursday, may briefly abate Thursday night as warm air takes over enough to change to rain, but is expected to switch back to freezing rain on Friday with potentially significant ice accumulations of a half inch, making for treacherous freeway conditions.
Stevens Pass will get a mix of everything -- with at least 6 inches of snow and a period of freezing rain as the snow levels drift higher and lower with the progression of the two storms. Above 4,500-5,000 feet, it's all snow and quite a bit of it. Up to 2 feet of snow is expected at Mt. Baker. Snow levels will crash Friday night after the second storm passes and cooler air mass returns, dropping to around 1,500 feet, changing freezing rain to scattered snow showers that will decrease Friday night.
So mountain pass travel over the next two days? Dicey. Be sure to plan ahead and check with the WSDOT pass conditions.
In the lowlands, it's all rain, and plenty of it. Forecast models predict roughly 1-2 inches of rain down here, and with the snow levels rising, enough runoff will occur in the mountains for to bring potential for minor river flooding. A Flood Watch is in effect for all mountain fed rivers in Western Washington except those in Whatcom and Skagit Counties. Greatest chance of a little flooding is on the Snoqualmie, White, Newaukum and Skokomish Rivers.
Rain tapers off Friday night and it should be a tranquil weekend that is mostly dry except for perhaps a few leftover showers Saturday morning.