No Sea-Tac Record For Rain-Free July, But Still Up For Dry Day Streak

Jul 28, 2017

A small storm of drizzle spoiled Seattle’s chances to break what KNKX weather expert Cliff Mass viewed as a significant record.

Thursday morning’s precipitation was just enough to be considered a "trace" of rain and cancel the chance for a rain-free July. But there is still a chance to continue a dry-day streak.

“This is this month we came close to beating an important record,” said Mass. That would be a full calendar month with no rain – which has never happened, in any season.

Trace Vs. Measurable

The specific location meteorologists are focused on is the measuring station at Sea-tac International Airport. And they distinguish between a "measurable" amount and a "trace" of the wet stuff.

Mass explains “measurable”precipitation by National Weather Service standards is a hundredth of an inch of precipitation.

“You can get a subjective feel for that, because when you get a hundredth of an inch, the concrete just gets this uniform wetness to it,” he said.

That wetness is close to what we had on Thursday, but didn't quite live up to "measurable".

“If you had less than a hundredth of an inch, but still rain, we call that a trace,” Mass says.

The measuring station at Sea-Tac has never gone a full calendar month without even a "trace" of rainfall.

Still In Line To Break 51-Day Record

He says despite the drizzle that ruined the stats for a record rain-free month, we’re still in the running for another big one.

“And that is number of consecutive days without measurable rain,” Mass said.

That record is 51 days.  Right now we’re at 41 days.

“And I think we have a shot at it,” Mass said.  “There’s no certainty but if we can go through into early August, with no measurable rain, we potentially could hit that 51-day record, and that would be pretty exciting,” he said.  

No Rain In The Weekend Forecast

Mass notes there’s no rain to speak of in the forecast.

“In fact, each day is going to be very similar to the next,” he said, with low clouds and a few sunbreaks all the way up to the crest of the Cascades.

He says those clouds will burn off Friday with temps reaching the high 70s.

Saturday, it will get a bit warmer and even sunnier earlier in the day.

“A little less clouds in the morning, temperatures getting up around 80, maybe low 80s. So another beautiful day,” Mass said.

He says expect more clouds on Sunday morning as a weak disturbance moves through Saturday night.

But he says those clouds will still burn off and temperatures will get up into the upper 70s – around 80 – on Sunday.

Even Sunnier Next Week

“And then as we get into next week – Monday through Wednesday -- a ridge of high pressure will build over the western United States and our temperatures will slowly go up, and by the time we get to Tuesday and Wednesday, it’ll be in the mid-80s and completely dry,” Mass said.

Mass says none of this is really that extraordinary for this time of year. What is noteworthy is that there has been relatively little lightning – due in part to that high pressure.  

Those dynamics have prevented a major wildfire season from starting in Washington. But Mass notes that could easily and very suddenly change, if there’s a even a single thunderstorm.

“So we’re going to have to watch this, because things are really ready to burn,” Mass said.

To hear an extended forecast, along with Mass's discussion of why some clouds produce rain while others don’t,  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.