Summertime in the northwest can provide a remarkably mellow atmosphere, with lots of clouds, temperatures that hover around 70 degrees and the kind of sprinkles that evaporate on your skin almost as soon as they land. Low clouds often filter the light and you can enjoy the soft focus all around.
That’s the kind of weather people in most of western Washington can look forward to for the next several days.
A SOFT-FOCUS WEEKEND
“It looks like a cloudy weekend, maybe a little bit of sun. An occasional sprinkle in the mountains, but not much more. And temperatures will be a little bit below normal,” said KNKX weather expert Cliff Mass.
This weekend, he says a weak trough of low pressure is coming in.
“That’s going to provide lift. I think there’s going to be a lot of low clouds – so, cloudy conditions. Maybe a few breaks in the afternoon. There might be a sprinkle or two, particularly in the morning and particularly on the western side of the mountains,” Mass said.
He says the temps will remain around 70 degrees, which is a bit below normal for this time of year.
“If you want warmth, go to eastern Washington,” Mass says. “It’ll be 80s over there.”
'PERFECT' CONDITIONS FOR STP CYCLISTS
Mass says this weather will be ‘perfect’ for the popular Seattle To Portland bike ride this weekend; the event’s thousands of participants (one of whom emailed us asking for Cliff’s take on the forecast for the ride) couldn’t ask for better conditions.
“I couldn’t imagine anything better. There could be a little sprinkle or two, but nothing serious at all,” Mass says.
He says it will be cool while they ride (mid 60s) with pleasant cloud cover, very little wind and only a few sprinkles, if any.
“So, all in all, I can’t imagine a better situation for STP,” said Mass (who is himself an enthusiastic bike commuter.)
WETTER FROM WEDNESDAY NIGHT
Mass does expect a shift starting Wednesday evening that will continue through Friday of next week, bringing real rain back to the region: another trough, this one much larger.
“Certainly in the mountains—and some light rain down in the lowlands,” Mass says. “So, things are going to go downhill later in the week, temperatures only getting into the mid- to upper 60s – so a real drop down.”
This weather will come as a relief to some folks who noticed an unusual amount of moisture in the air Wednesday and Thursday. Mass says many folks complained to him that they were breaking out in sweat after minimal exertion. The air was sticky – even with temperatures mild, in the 60s and 70s.
HUMIDITY OVER… FOR NOW
Mass confirms that the humidity rose to unusual levels. It’s measured by the so-called ‘dew point,’ which tells us at what temperature the air becomes saturated when it’s cooled down. The higher it is, the more moisture there is in the air.
"The dew points on Wednesday and Thursday got up to the mid-60s – even got to 70 at McChord,” Mass says. “That’s very high. Normally during the summer, our dew points are in the upper 40s and 50s. That’s why we’re nice and cool and comfortable around here.”
Mass says dew points in the upper 60s and 70s are more like what people routinely experience in summer in the eastern United States.
The source of our humidity was a combination of factors: a surge of air came in from the southwest, bringing water vapor with it off of the Pacific Ocean. That combined with drizzle. And the ocean was a couple of degrees hotter than normal.
“So, all of these things came together to give us relatively unusual conditions, with very high dew points,” he said.
Mass says as of Friday morning, conditions had improved; the dew points dropped down into the mid-50s, a much more comfortable situation. But he said this scenario from earlier in the week could happen again soon.
“I don’t think it could get that bad too quickly, but I’ll be watching Thursday and Friday of next week – we could see it again.”
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.