Low clouds have lingered over much of the Puget Sound region in recent days, the latest evidence that this summer stands in stark contrast to the hot, smoky, straw-hat weather of the past two years.
KNKX weather expert Cliff Mass says Friday temperatures will only get into the lower 70s. And he says the weekend will be dominated by more of those lower temps, thanks to the presence of an upper level trough.
PERSISTENT LOW PRESSURE ALOFT
The trough means there is low pressure high above us. It brings with it the chance of more showers in the region and even some stormy weather. Mass says he expects the main thunderstorm action this weekend to hit Friday night into Saturday morning.
“I expect a line of thunderstorms – pretty vigorous ones – to move up from the south," Mass said. "The Cascades will get it. And I think that Western Washington will get some of this thunderstorm action."
And he says Eastern Washington will be hit even harder.
Saturday will get cooler, with temperatures around 70 and more thunderstorms. Then, on Sunday, Mass says the trough will move through, leaving mostly cloudy weather and temperatures that will eek back up to 73 or 74.
“So, we’re going to get a pretty significant hit of precipitation on Friday night – Saturday morning," he said. "But there could be showers the whole weekend."
If that makes you wonder where summer went, you’re not alone. Mass says he can explain the cause of the gloomier weather.
'VERY DIFFERENT' SUMMER
“This summer is very different than last summer,” Mass said. “And we’ve had a very, very persistent feature.”
He points to the upper level trough that’s paying the region a visit this weekend. It's not the first time this season and it won't be the last.
“That’s been stationed right off shore on the eastern Pacific. And that has been bringing in cooler air, moister air this summer – it changed the whole character of it,” he said.
Once in a while, the trough moves in, bringing the cooler weather in with it.
“And this is going to happen again and again this August,” Mass said.
This is in contrast to the ridge of high pressure that was the dominant feature for the past two summers. It brings in blue skies, dry weather and warmer temperatures that promote wildfires.
Mass says researchers are actively studying why the trough has been hanging where it is. There’s no cycle or correlation with things such as La Niña or El Niño that anyone has pinpointed yet. All they know for sure right now is that it has been in place for about a month and a half.
And Mass says, according to the latest long-term forecast from the highly trusted European Center’s 46-day forecast, the wetter-than-normal forecast that has been panning out all summer so far will continue for the next month and a half.
COOLER AND WETTER THROUGH SEPTEMBER
“So, it looks like – going through early September – we will be wetter than normal,” Mass said. “This trough will still hang out offshore and once in a while, some rain will come through.”
That means July, August and September will shape up to be wetter and cooler than normal this year, Mass says.
On the up side, the risks of major wildfires and smoky air are significantly diminished.
“Out temperatures will be held down – particularly here in Western Washington – and it should restrain the wildfires,” Mass said.
He says there's still the danger that once in a while, when the troughs come through, they bring thunder and lightning that can spark wildfires when forests and grasses and other fuels are dry – especially in Eastern Washington.
But the major risk of smoke and severely polluted air is not as much of a concern, Mass says, because the trough is also associated with wind patterns that keep much from blowing toward the state.
“When we have a trough, we have southwesterly flow coming into us. So, in general, that will keep the smoke out of western Washington,” Mass said. “Now, it’s not as good for Eastern Washington, because that’s where the fires will tend to be. So they can get localized smoke. But I think this is going to be a much better smoke year.”
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.