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Get Ready For ‘May Gray’ and ‘June Gloom’

Tim Durkan
Tim Durkan Photography
Moody skies over Seattle on February 25, 2018.

Here are some upsides to cloudy weather: Cloud cover creates a soft light that's great for photographers. It’s harder to get a sun burn. And clouds can be really fun to look at.

Many of us may need a few reminders that clouds aren't so bad as we enter what could become an extended period in which low clouds and cooler temps dominate in the greater Puget Sound area.

“May Gray leads to June Gloom,” explains KNKX weather expert Cliff Mass. And he says Friday will be gray and cooler than earlier in the week.

“It’s going to be pretty cloudy.  Last night (Thursday), we had a very active onshore push of marine air. You may have noticed, late in the day, the southerly winds started picking up. And the clouds started surging in over the region,” Mass said.

“And so, those clouds that were offshore, they moved in to the Puget Sound and western Washington region – so we’re cloudy today, temperatures will only get into the lower 60s,  So, a much, much cooler day after that onshore push.”

Partly Sunny Saturday

Mass says Saturday will be only partly cloudy, and it will be the best day of the weekend.

“Temperatures will go up into the mid- to upper 60s,” he said. “And it’s going to be dry, there’s no rain going on here.”

Sunday, Mass says there will be another onshore push, bringing more marine air in, but just a minor one.

Warmer Sunday

“An upper level trough is coming through, particularly later in the day,” Mass said. “So there might be a little bit of sun in the morning, the clouds will come in later on Sunday.”

But he says the air will be much warmer. And temperatures should get up to 70 degrees.

“Even lower 70s on Sunday,” Mass said.

Improving As the Week Begins – But Expect Rain Wednesday

“Now, after that, actually we should have an improving trend. High pressure builds in again. Clouds will retreat. And temperatures should get into the lower 70s on Monday and Tuesday.

On Wednesday, though, Mass says another trough comes in and rain will be in the forecast.

This back and forth of the weather is tied to the influence of pressure in the atmosphere, Mass explains. That’s the heart of the systems that can cause lengthy periods of low clouds, often referred to as ‘May Gray' and ‘June Gloom.’

Mass says this is typical spring weather in Western Washington.

“What happens is, the low pressure areas that dominated over the eastern Pacific get replaced by high pressure. So high pressure – subtropical high pressure – builds northward into the eastern Pacific’” he says.”

Mass says this is what produces vast areas of low clouds, such as those visible on satellite pictures late Thursday or early Friday.

“A tremendous sheet of low clouds over the eastern Pacific…Thousands of miles in extent. And that’s because of the high pressure,” he explains.

Mass says during April and into May, this gigantic bank of low clouds forms offshore. It tends to get pushed into the lowlands , where people live.

“And that produces May Gray during this month and June Gloom During next month,” Mass says.

“So, we have a lot of low clouds during this late Spring/early summer period. And that’s ironically due to the high pressure offshore.”

To hear the full conversation, including Cliff’s explanation of how and why the summers in western Washington tend to be mostly sunny, 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.

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