Gray skies, rain showers and possible thunderstorms are in the forecast again. It’s a pretty typical for this time of year in the Pacific Northwest, where most people rattle off phrases such as "June Gloom" and "June-uary" to describe this kind of weather.
The exception here is thunder and lightning. Intense storms that are common in other parts of the country are rare here.
The storms predicted for this weekend will be tame compared to the incredible displays last Saturday, which one researcher noted was the darkest day of late May in 20 years. Incredibly tall, dark clouds produced continuous thunderstorms for nearly two hours.
“Lots of lightning — hundreds of lightning strikes,” says KNKX weather expert Cliff Mass. He noted the strength and duration of the storms was one aspect of what made the day so remarkable. Even more striking, Mass says, was the height of the clouds, as they appeared on the radar.
“There were a few echo tops of these thunderstorms — the top of the precipitation of the thunderstorms — that got up to 49,000 feet,” he says. “I have never seen that around here before. That’s the tallest thunderstorm I’ve seen hitting Western Washington.”
In Eastern Washington, the storms hit a little later in the afternoon, but reached even higher into the sky and showed up with so much intensity that the weather service classified them as “severe thunderstorms,” with very strong winds, including some that started rotating. They also produced large hail — some as large as golf-balls — that pummeled Eastern Washington and extended into Eastern Oregon.
“There was outflow winds from these thunderstorms that in some places got to 60-75 mph,” Mass says, “so these were really intense storms.”
Mass says the main reason we don’t normally get these storms is our proximity to the Pacific Ocean, which cools the air and prevents it from retaining moisture. The main ingredient in big thunderstorms is lots of instability in the atmosphere, which is normally associated with warm, moist air at the surface.
Last Saturday, all the elements needed to generate major thunderstorms came together in an unusual way, with a trough of upper level pressure moving through, drawing in warm, moist air from the south, which is rare.
“And so we had all these ingredients together," he says. "And that produced these intense thunderstorms."
You can listen above to hear the full discussion.
NOTE: Cliff Mass will give an online talk on the "Mathematics of Weather Prediction" Sunday, June 7 at 1 p.m. It’s geared toward middle- and high-school students, but anyone can join. Click here to register. Registration closes at 9 p.m. on Saturday, June 6.
The weekly KNKX feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and repeats twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX’s Environment reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences and a renowned Seattle weather prognosticator. You can also subscribe to a podcast of “Weather with Cliff Mass” shows on Apple, Spotify and Google