20-year lightning storm unlikely to repeat, but more heavy rain is coming to the Northwest | KNKX

20-year lightning storm unlikely to repeat, but more heavy rain is coming to the Northwest

Sep 13, 2019

Lightning lit up skies around the Puget Sound on Thursday night, and another big rainstorm is on its way to Western Washington. But KNKX weather expert Cliff Mass says none of the incoming weather systems are likely to outshine the extraordinary display of lightning that hit the region last Saturday night.

“It was the greatest lightning display we’ve had in 20 years,” Mass said. “We have to go back to 1999 to have anything that’s even comparable.”

There were thousands of lightning strikes all over Western Washington. Mass calls it a “perfect storm — of lightning,” adding that a number of factors had to line up to make it happen.

WHY ALL THAT LIGHTNING?

“The setup was just perfect,” Mass said.

There were two main ingredients that combined to make it happen, he says: extremely unstable air (bubbling up into cumulous and cumulonimbus clouds – the harbingers of thunder and lightning storms) and an incoming weather system from the southeast that tilted at just the right angle to push mountain thunderstorms down into Western Washington and over the ocean offshore.

And on top of that, Mass says, the ocean’s surface is currently warmer than normal because of a persistent marine heat wave that NOAA warned people about last week (Mass calls it "Blob Jr."). He says that gave extra power to the storms and made them produce more lightning.

“We had water that was about 5 degrees above normal offshore," Mass said. "That supercharged the lower atmosphere with lots of moisture, which enabled these thunderstorms to be even stronger."

As of Friday morning, he added, Blob Jr. appeared to be weakening and the water cooling down.

“And I expect it to weaken as the normal storminess re-establishes itself over the Pacific Ocean,” Mass said. He expects more of that to come in over the weekend, especially on Saturday night or early Sunday morning.

CLIFF’S WEEKEND FORECAST

Friday: Highs around 70 and partly cloudy. Maybe a few sprinkles in the mountains, “not too bad,” he says.

Then, the weekend gets progressively wetter with "one system after another" coming in.

Saturday: “generally OK.” Cloudy to partly cloudy, highs in the upper 60s, dry most of the day except in northwest Washington, where some morning showers may come through.

Saturday evening–Sunday morning: The real action comes in. “An extremely powerful, extremely wet front is going to move through,” Mass said. It will bring very heavy rain to the region.

“It’s going to be a drencher – some places will get a half an inch or more,” he said. “And maybe a little bit of wind with that, so a pretty intense system that will move through sometime around lunchtime on Sunday.

Sunday: wet and showery morning, yielding to possible afternoon sun, but temperatures only in the lower-mid 60s. “A real change,” Mass said.

Monday–Tuesday: Showers and partly cloudy, followed by another storm front maybe coming through later on Tuesday.

The good news, even for people who don’t love the rain? Wildfire season is effectively over. “The whole area is going to be drenched,” Mass said.

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.