An atmospheric river is going to impact the region for midweek. This is a stout area of moisture streaming in off the Pacific.
Previous atmospheric rivers have brought warmer air and heavy rain (even in the mountains), but this one will have cool enough temperatures to keep the moisture in the mountains mainly in the form of snow.
Additionally, a low-pressure system will skirt the northwestern sections of the area later in the day on Wednesday, inducing some strong southwesterly winds to the area, eventually turning westerly.
LOWLAND WIND AND RAIN
For the lowlands, expect rain to increase through the day on Wednesday and become heavy in spots Wednesday afternoon and evening. The Friday evening commute is likely to be quite messy with standing water and gusty winds.
Lowland wind gusts in the 30-40mph range are expected mainly after 2 p.m. on Wednesday through midnight Thursday morning. Isolated wind gusts to 50 mph are possible.
A Wind Advisory has been issued for all lowland locations for this threat late Wednesday into Wednesday night. Sporadic power outages are possible.
MOUNTAIN BLIZZARD
It will be windy in the mountains, too. A Blizzard Warning is out for these impacts in the Cascades and Olympics, with the worst of the conditions from Wednesday afternoon through early Thursday morning. A blizzard is defined as wind gusts or sustained winds of 35 mph or stronger with visibility in falling or blowing snow of one-quarter mile or less, with conditions lasting at least three consecutive hours.
The storm in the mountains late Wednesday and Wednesday night will likely fit that definition!
Two to four feet of snow will fall from early Wednesday through Thursday in the mountains, with isolated higher amounts on higher peaks. The passes will be difficult to impossible to traverse during this period, and avalanche danger will be very high. Winds in the mountains will also gust to 45 mph or stronger, creating whiteout conditions and blowing and drifting snow.
While this snowfall is extreme, we would need (given location) anywhere from 40-70+ inches of snow to get the snowpack back to “normal” for this time of year. We’re not likely to get back to average with this storm, but it will put us much closer! Right now, we’re at our worst snowpack conditions since 2015 or 2005, depending on location.
Avalanche danger will be very high through the end of the week, and skiers and boarders should always travel with a buddy and stay out of backcountry areas when the danger is very high.
Some snow will continue in the mountains later Thursday and Friday as well, with lowland rainfall. The snow in the mountains could be heavy at times, but blizzard conditions aren’t expected. However, pass travel will still be very difficult, especially on Friday
FLOOD THREAT LATE IN THE WEEK
Later in the week, the Skokomish River in Mason County will likely reach flood stage and other rivers will be running high, with the Skookumchuck and Chehalis Rivers in flood stage by late Friday or Saturday.
The weekend could hold some drier times though some rain chances remain. It looks markedly warmer next week with the potential for rainfall again, not only in the lowlands but in the mountains too, which could continue river flood potential.
The long-range forecast problem is the anticipated setup of another atmospheric river late week into early next week, with eventually milder temperatures.
The trend in forecast models has been to direct the main plume of moisture up into British Columbia, but this isn’t certain. If the heavy rain is focused farther south across our area, we could be looking at some additional river flood impacts.
We’ll watch that as we get closer.