Scott Sistek 
Did this summer seem more humid than usual around Seattle? It was a frequent comment/question I received throughout the summer.
Well, now I have an answer, and it’s: Yes.
Ben Noll, the excellent meteorologist who works as a Weather Reporter for the Washington Post, recently posted a research article (linked in comments below) on how America in general is becoming more humid as the climate warms.
His focus, rightfully so, was on highlighting places east of the Rockies where dew points can reach extreme and dangerous levels of 70 or 75+ degrees. (The dew point is the temperature at which air becomes saturated and is a factor in humidity. Higher dew points usually mean higher humidity levels and more uncomfortable weather.)
But Seattle and the Pacific Northwest don’t get those dew points thanks to A) the cool Pacific Ocean nearby and B )No access to the warm Gulf moisture that fuels the humidity across the central and eastern U.S. Seattle’s record high dew point is 66.
So we didn’t make the cut for his article, but I asked if he could share his humidity data for out here since so many people remarked it was such a humid summer.
SO WERE WE LITERALLY CAUGHT IN A STICKY SITUATION?
Noll says King County’s average dew point this summer (June 1-August 31) was 51.2 degrees — sounds low, but as an overall average, its the 3rd-highest since these records began in 1981.
Snohomish and Kitsap County were even worse, ranking 2nd-most humid. Whatcom, Skagit and Pierce Counties were all top 5 out of past 45 years.
If you look up and down the chart (image below) you’ll see plenty of counties in Western Washington were in the top 20th percentile for a humid summer, if not top 10%.
(You TL;DR folks can probably stop here and scroll over to the latest crazy trends on IG, like me earlier looking up what in the world does “6-7” mean. Thanks for reading! 🙂 For those with more time… let’s dive further!)
WHY SO HUMID? ⛈️
I suspect the culprit was mostly due to August when we had several days of anomalous monsoon moisture feeding our way from the Desert Southwest.
It is very difficult to get high dew points here because the two large-scale weather patterns that typically take up the vast majority of our summer days ironically both work to suppress high dew points.
Most of the time, the flow is off the Pacific Ocean — sure, that brings moisture, but it also brings cooler weather (our “natural air conditioning”) because those water temperatures are in the 50s. We don’t notice higher humidity levels when the temperatures are lower because we’re not overheating and trying to sweat. Foggy days in the 50s and 60s could have 100% humidity but not “sweaty” heat + humidity.
On days we get hot, it’s usually the east wind that pushes back the cool, ocean air. But that air is coming from arid Eastern Washington, so that air is dry to start. And then it dries further when it comes over and sinks down the Cascades. So our hot summer days are usually also very DRY summer days like a California heat, not a soupy Louisiana heat.
The monsoon is our one humidity achilles heel. When there’s plenty of monsoon moisture in the Desert Southwest, a large low pressure area centered just so can bring a south/southeasterly flow into our area, dodging both the cooling powers of the ocean and the drying powers of the Cascades, so we get warm AND humid.
And that pattern got stuck for weeks earlier this summer. Remember all those days with those thunderstorm chances and the lightning in the Cascades and Olympics? Monsoon mayhem.
(I also suspect a minor contributing factor is the water off our coast is a bit warmer than average right now so that can even give us a little warm boost on even our west wind days.)
HANDY DEW POINT GUIDE (WITH FLAMINGOS?)
Years ago I made a handy summer dew point temperature guide for Seattle:
< 46 degrees: Hot and dusty
46-53: typical and comfortable
54-56: slight hint of mugginess but not bad.
57-58: Noticeably muggy
59-63: Yuck
>63: Break out the plastic flamingos.
(P.S. Still kinda lost on the whole 6-7 thing )