Keep your parkas handy or maybe an umbrella if you’re trick-or-treating this weekend. The forecast is full of rain — very heavy rain in places, says KPLU weather expert Cliff Mass.
“It’s going to be really wet,” he said. “It’s pretty scary if you’re going to go hiking or go up into the mountains,” so you might want to rethink such plans.
Mass says a series of “very wet systems” is coming in off the Pacific Ocean, and there’s “a tremendous amount of moisture behind it.”
Three Waves Of Wet Stuff
The wind and wet weather that swept through Seattle early Friday was the first wave to come through. Mass says the next will arrive Friday evening and continue through Saturday morning. Then there may be a break sometime during the day, but another is due to arrive on Halloween evening or night.
“And as we get later into the weekend, an upper level trough is going to sink down through us,” Mass said. That will cause temperatures to drop, “and we’re not only going to get some moisture, but we could get some snow in the higher elevations,” Mass said.
A Long Time Coming
Mass says the weather patterns coming in are the kind that cause excitement for meteorologists.
“This event is going to be the most significant that we have had for a very long time,” Mass said. “Before the weekend’s over, some places in the mountains will have 4 to 8 inches of rain - and in fact, I wouldn’t be surprised if some had a foot - particularly in the higher elevations,” he said.
As for snow, Mass says the North Cascades could get 6 inches to 1 foot and there are places in British Columbia such as the Rockies that could get even more than that.
“So, we’re seeing first really wet system coming in,” Mass said.
Flood Risks
That also means a substantial risk of flooding on many rivers.
“When you’re hit by this much rain, this fast, the rivers are going to rise substantially,” he said. “And a number of the major rivers in western Washington, draining off of the Cascades, could hit flood stage — we’re talking about the Snoqualmie, the Skykomish and others.”
“So people really have to watch that,” he warned. “If you’re near the rivers, you have to be ready for them rising very rapidly this weekend.”
Replenishing Water Supplies
Mass says though the timing may be inconvenient for some folks, the precipitation is badly needed after a long period of drier than normal weather.
“This event will go a long way to stopping the decline and start refilling some of the reservoirs, like the reservoirs that support the city of Seattle, the Yakima River basin — they’re all going to get significant water from this,” Mass said.
In this week’s podcast, Mass describes the past summer’s weather as a "global warming stress test” that can show us how ready we are for climate change in the Pacific Northwest. You can hear the whole conversation by clicking on the “play” icon at the top of this post.
The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU Environment Reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.
