‘June-uary’ becoming just June? Why Western WA is losing its marine clouds

I recently posted an article addressing a listener’s question about what is the marine layer. A reader responded with the following:

Is it just my imagination, or does the Puget Sound region have fewer days with marine clouds than we had years ago? My childhood memories are of waking up to heavy marine clouds many days in June. Quite often it didn’t burn off until 2 p.m.”

Good point! I do not have any specific statistics regarding the trend in the number of Puget Sound region days with marine clouds, but I do have some information to share.

First, an oceanographer reviewed global temperatures from the 1950s to 2010. He found that on a worldwide scale, summers are now about three weeks longer, starting earlier and finishing later. The other three seasons have become shorter.

More on local heat waves: When will 2021’s ‘Heat Dome’ return to summer in Seattle?

The 2010s were also the warmest decade on record, continuing that longer summer trend. The 2020s is on pace to break that record after more warmer-than-ever months have been recorded globally.

Second, in the latter half of the 20th century, Seattle averaged around three days in the 90s. So far this century, the number of 90-plus degree days climbed to five days. In 2022, there were 13 of these “hot” days, the most recorded in one year.

On June 28, 2021, Seattle-Tacoma International Airport (SEA) soared to 108 degrees, crushing the previous all-time high temperature record that occurred on July 29, 2009 of 103 degrees.

Third, why is this warming trend occurring? Why are we witnessing more excessive heat events not just in this region, but around the world?

One major reason is the rising amount of the significant greenhouse gas — carbon dioxide (CO2) — a bi-product from burning fossil fuels. The National Oceanic and Atmospheric Administration (NOAA) released an annual report earlier this month on the average amount of CO2 measured at their weather station on Hawaii’s big island, Mauna Loa, a site in the middle of the Pacific Ocean, isolated from any industrial or auto emission sources.

NOAA reported the average amount of CO2 at Mauna Loa for the entire month of May was just under 427 parts per million (ppm) – a new record. Each year, a new record has been set and has been steadily rising since the 1960s. The Mauna Loa weather station has been in place since the 1950s.

At the beginning of the industrial age in the late 19th century, ice core measurements revealed about 280 ppm of CO2. So the amount of this greenhouse gas has risen dramatically over the past 130-plus years and is helping to produce the warming including longer and warmer summers.

Mount St. Helens: Seismic activity brewing with more than 350 earthquakes since February

All this information leads to why there are fewer days with marine clouds in the Puget Sound region. An overall warmer air mass reduces the presence of marine clouds. That decrease may seem subtle, yet it has been noticed by long-time residents.

Western Washington is fortunate to have a cooling source nearby, the Pacific Ocean. That resource helps moderate temperatures from becoming excessively hot during our longer summers while many other parts of the nation are not so fortunate. Yet, when the low-level flow turns offshore and those cooling breezes are reversed, it can and does get hot.

Thank you for your question related to the recent marine layer story. If you have a Western Washington weather question, send it along to feedback@mynorthwest.com and your question may be in a future story.

Ted Buehner is the KIRO Newsradio meteorologist. You can read more of Ted’s stories here and follow him on X, formerly known as Twitter.