WASHINGTON — By Thursday morning, most of the rain will be gone, although a few isolated showers could linger during the day.
The best chance for those will be near the Olympic Peninsula and coast, as well as around a possible convergence zone in Snohomish County.
Otherwise, Thursday should offer us a bit of a breather, with some sunbreaks possible and highs climbing into the mid to upper 50s.
But don’t get too used to the break.
Another weather system associated with a weakening atmospheric river will move into the region Thursday night into Friday. The heaviest rain with this system looks to be aimed farther north toward Vancouver Island, but we’ll still get another round of rain across Western Washington along with some blustery winds, especially along the coast and across our northern areas.
Rain chances will linger through Friday, and with leaves continuing to come down, drivers should be on the lookout for areas of standing water. It doesn’t necessarily take an extreme amount of rain to create problems this time of year. Leaves can quickly clog storm drains, allowing water to pool on roads during heavier downpours.
Rain chances should exit by Saturday morning, giving us a brief dry break to start the weekend. And it will actually be a pretty balmy November day, with highs climbing into the 60s in some spots.
Unfortunately, the break won’t last long.
A more potent system is expected to arrive Saturday evening and Saturday night, bringing another round of heavier rain and, more notably, stronger winds.
At this point, this does not look like a serious windstorm, but gusts could top 45 mph along the coast, with gusts over 30 mph possible across parts of the interior of Western Washington. Since many of our trees still have some leaves on them, they’ll catch more of the wind than they would later in the season. That means this system bears watching, particularly if the forecast trends any stronger. The details on the wind threat should come into better focus over the next day or so.
Fortunately, the main system looks like it will move through by Sunday, leaving behind blustery showers and cooler air. Highs Sunday will settle back into the low to mid 50s.
We’ll then get another brief dry break Monday.
One thing we won’t have to worry much about with this stretch of storms is significant mountain-pass snow. Snow levels should generally remain at or above 5,000 feet through the rainy stretch tonight into the weekend, meaning we’re expecting rain rather than snow for the major passes.
After Monday, things could get even more interesting.
The overall weather pattern looks quite active across the Pacific Northwest next week, with the potential for additional potent storm systems and atmospheric rivers coming off the Pacific. There is still considerable uncertainty over exactly where those systems will track and, perhaps more importantly, where the atmospheric-river moisture plumes will be aimed.
Some forecast model solutions would essentially brush Western Washington with these systems while directing the heaviest rain and strongest storm activity into British Columbia. Others put our region much more squarely in the crosshairs.
Those differences are significant so we’ll be watching how the forecast evolves over the next several days.
Either way, November is starting to act like November. We’re entering the time of year when active, rainy and windy stretches become much more common around Western Washington, and there appears to be plenty more stormy weather headed our way.
So, what exactly is an atmospheric river?
We’re going to be talking about atmospheric rivers quite a bit over the next week or so because most of the weather systems headed our way will have some connection to one.
An atmospheric river, or AR, is essentially a long, relatively narrow corridor of concentrated moisture in the atmosphere. Think of it as a plume of moisture being transported from the Pacific toward the West Coast. When that moisture runs into Western Washington and is forced upward by the Olympics and Cascades, it cools and condenses, helping wring out sometimes significant amounts of rain.
Not all atmospheric rivers are created equal, though. Some are relatively weak and simply give us a good soaking, while stronger or slower-moving ARs can produce prolonged heavy rain, river flooding and an increased risk of landslides. Where that plume of moisture is aimed also makes a huge difference. A shift of even a couple hundred miles north or south can determine whether Western Washington gets the brunt of the rain or whether the biggest impacts end up over Vancouver Island and British Columbia.
That’s going to be an important part of the forecast over the next week.