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Rare thunderstorms rolling in, followed by sun and heat; and a D-Day weather lesson

"Sky theater" provided by mother nature Wednesday, June 5, in Seattle.
Tim Durkan
Tim Durkan Photography
"Sky theater" provided by mother nature Wednesday, June 5, in Seattle.

Many people woke up to big patches of blue sky in the Puget Sound region Friday, especially in the South Sound. But KNKX weather expert Cliff Mass says the sun breaks will yield to cloudier weather as low pressure moves into the region. And a rare batch of thunderstorms is expected to douse and excite parts of the state.


Mass said most of the rain is expected Friday, likely concentrated in the South Sound and Southwest Washington, which will get a “quarter to a half an inch.”

“It’s going to be exciting for some people,” he said. “An area of very unstable air is moving in off the Pacific. And so, I am expecting some very serious showers — including some thunderstorms to form somewhere between Seattle and down to the Oregon-Washington border.”

Mass says to expect lightning and thunder: “Somebody’s going to get it.” It will be good for the state’s drought situation, he added.


Saturday will transition to warmer weather, with temperatures reaching the mid-60s. But by the end of the day, it should be sunny and even warmer. Sunday, Mass says temperatures will reach about 70 degrees, beneath partly cloudy skies.

Next week, he expects a big shift to major warmth as a large ridge of high pressure will build over the northeast Pacific, causing temperatures to spike.

“By the time we get to Wednesday, we could be in the mid-80s, even the upper 80s away from the water, so really warm temperatures,” Mass said. That will be followed by marine air Thursday, dropping temperatures back to the lower 70s.

“It’s going to be a ride up and down this week,” he said.


The strength of the sun also is a major force behind the thunderstorms expected Friday, Mass said.

“Thunderstorms are relatively rare here,” he said. “On the West Coast, we get less than 10 a year, in contrast to the eastern United States.”

But, he says, when we do get them they come from instability in the atmosphere — which is associated with big differences between temperatures at ground level and up higher in the sky. Those conditions often happen in late spring.

“This time of the year, the sun is quite strong,” Mass said, causing the surface to warm. “When we do that and cool air comes in aloft, which is happening right now, that produces a large change of temperature in the vertical. And that produces convection — when the atmosphere starts bubbling up.”

Picture the bubbles forming in a pot of simmering oatmeal to get the idea, Mass says.

The other ingredient needed, Mass says, is something to give “a little bit of lift to get these thunderstorms and this convection going. And we’re going to get that, too.”

Mass says an upper level trough will move in Friday, providing the uplift that can help get thunderstorms going.

“There’s no guarantee at any particular location that you’ll get a thunderstorm,” he said, “but I will almost guarantee that somebody will somewhere in Southwest Washington.”


This week 75 years ago, the threat of stormy weather around the beaches of Normandy — and the skill of forecasters predicting and analyzing it — played a key role in defeating German troops.

“It was very important,” Mass said. “June 6, 1944, was a marginal day for the invasion, but it was just good enough. And the German forecasters thought it would be too stormy.”

In fact, Mass said, the man leading German troops — Field Marshal Erwin Rommel — even returned to Germany because he thought the weather wasn’t going to be ideal for an invasion. But allied weather forecasters knew otherwise.

“And one of the reasons that they had it right and the Germans didn’t,” Mass said, “was that the Allies had all the weather observations over England and over the Pacific.”

The storm was coming in off the Atlantic and the Germans lacked sufficient observations upstream, Mass say; the key advantage was the Allies’ additional information — data reported from all over England, from weather ships and from ship traffic over the Atlantic.

“I think that was the ingredient that gave us the edge,” Mass said.

To hear the full conversation, 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, anda popular weather blogger. You can also subscribe to podcasts of Weather with Cliff Mass shows, viaiTunes or Google Play.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to