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Rain returns as region recovers from arid March, but UW team shines bright in forecasting contest

Tim Durkan
Tim Durkan Photography
A friday night sunset as seen from Seattle in January, 2019

Stay indoors or get out the Gore-Tex this weekend if you’re going outside in Western Washington. KNKX weather expert Cliff Mass says a triple whammy of weather systems will douse the region, providing some relief from our record-dry March and only a few dry periods over the next few days.

“We’re going to have three rain events over the next 72 hours,” Mass said Friday morning. “The drought of March is going to be over.”


The wet weather started with a frontal system hitting the coast early Friday. It was set to arrive in the South Sound region before noon says Mass, who is a professor of atmospheric sciences at the University of Washington.

He said that system will move into the entire region in the course of the day, wetting things down quite a bit. People should expect to get several tenths of an inch of rain in most places.

“It’ll be a rainy day,” Mass said. “The system will also bring some wind. It’ll get gusty — winds gusting to 10 to 20 miles per hour.”

But he says that first rain event will probably be done by dinnertime. And there should be a break overnight.


The next system will be a bit stronger and will arrive early Saturday.

“It’ll be pretty much a rainy day on Saturday — maybe a half an inch of rain. The wind will pick up maybe to 20 or 30 miles per hour for gusts,” Mass said. Again, a break comes in after the system moves through, sometime in the later afternoon.

But then the strongest system comes in on Saturday night into Sunday morning. Mass says this one will bring half an inch in many places, but even more in the mountains.


“There could be several inches,” he said of rain hitting the mountains. “And that’s going to be driven by an atmospheric river – one of these plumes of moisture coming out of the sub-tropics. So, expect lots of rain Saturday night-Sunday morning.”

Mass says that third system should move through sometime in the midday on Sunday, so most folks in the region can expect a break from the rain on Sunday afternoon.

“The only exception will be our old friend the Puget Sound Convergence Zone, which will develop somewhere between Seattle and Everett,” Mass said. “There’ll be a band of precipitation there — showers there.”

The convergence zone happens when large scale air flow coming from the west hits the Olympic Mountains and splits, then converges on the other side, producing rain.

Mass says there could also again be more rain in the mountains late Sunday.

“So, we have three systems to get through,” he said. “Then as we get into Monday — Tuesday, we should have a break. A ridge of high pressure builds in, we should dry out.”

But it looks like more wet weather will come in again, later in the week.

“So, March was the second-driest March in history," Mass said. "I don’t think that’s going to be true of April. I think we’re going to be at least normal by the time all this is over."


Mass teaches Atmospheric Sciences 101 at UW, and just finished with his latest group of students last quarter. An exercise he does every year illustrates what he calls “the wisdom of groups.”

Mass challenges his students to enter a forecasting contest in which everyone individually tries their hand with the skills they’ve learned, by predicting the weather at Seattle-Tacoma International Airport.

Keep in mind that these students are all essentially amateurs.

“The amazing thing is, at the end of the quarter, when we look at the scores, we find that a consensus forecast — which is an average of all these untrained students — does extremely well,” Mass said. “In fact, their average forecast beats the National Weather Service.”

Mass says the reason this group of 50 to 100 students almost always beats the experience and expertise of the professionals is the power of crowdsourced knowledge. The average of their predictions captures a wide variety of opinions and sources of knowledge, but also smooths out extreme calculations — in which a professional forecaster might go out on a limb.

“If you average all of those together, it’s really hard to beat,” Mass said. Though, he added, predictions of unusual or extreme weather likely will be more accurate coming from seasoned professionals.

“But on average weather and looking at this for a few months, the forecasts by the students are the best. It’s really amazing.”


A team of UW students also proved their forecasting skill this week, winning a national competition in which universities compete to deliver the most accurate daily forecast for cities all around the country. It’s called the WxChallenge. Mass said the UW department ranking at the top of 36 teams is a huge achievement.

“But this achievement is not only based on the skill of the forecasters, it’s also based on the technology that some of our students have developed,” Mass said.


Doctoral student Jonathan Weyn claimed the top individual prize in the competition. He developed a tool called MOS-X that uses machine learning, an advanced form of artificial intelligence, to aggregate statistics from weather models to get the most skillful forecasts. Mass expects machine learning to be a big part of weather forecasting in the future.

“We spend a lot of time getting good observations and many observations, from satellites and other things. We also have very good models that we’ve developed," Mass said. "But there’s another stage in forecasting that many people don’t know about. It’s called post processing."

That’s the process of taking all the forecasts and observations and combining them in an optimal way to make the best predictions.

“And it turns out that although humans are pretty good at this, machine learning or artificial intelligence…in fact is probably better.”     

The UW team advanced to the tournament round of the WxChallenge, which started April 1 and continues through April 26.

To hear the full conversation, you can click on the "play" icon at the top of this post.

Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX 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 podcasts of Weather with Cliff Mass shows, via iTunes or Google Play.

Bellamy Pailthorp covers the environment beat for KNKX, where she has worked since 1999. From 2000-2012, she covered the business and labor beat. Bellamy has a deep interest in Indigenous affairs and the Salish Sea. She has a masters in journalism from Columbia University.