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Dirty Fireworks, Cloudy Skies Typically Herald The True Start Of Summer In The Northwest


Inevitably, fireworks start going off in the first week of July, even before the Independence Day holiday has begun. 

They’re not just loud, says KPLU weather expert Cliff Mass, they’re dirty.

“We often see a spike at the air quality measuring stations of very small particles (of pollutants,)” Mass said.

He notes there is typically a gigantic jump in levels measured on the 4th of July later in the day.

“And some places it’s the worst air of the year,” he said.

And strangely enough, in terms of meteorological records, Mass says July 4th tends to be a little bit wetter and cloudier than the days before and after.

“Just a little bit – no one’s figured that one out,” he said.

On the positive side, he says July 4th marks the official start of the real summer in terms of that hot, dry pattern that most people wait for – the time for barbeques and swimsuits.

He says it really is the break between the “June gloom” that dominates before then and a period when the weather improves rapidly and radically.

“And by the end of July, we are at the driest, warmest period of the whole year, so it’s this amazing transition in the weeks after the 4th of July,” Mass said, “to our classic, perfect summer weather.”

The force behind it is a change in the atmospheric situation; an area of high pressure commonly referred to as the “East Pacific High” moves in and causes wind patterns to shift so that more dry, warm air dominates, coming from more from the north and east and replacing the marine layer that comes from the ocean before then.

The heat that results can really rev up fire season, so it’s a good time to check your roof and yard for fire wise features.

Mass says this year’s fire season is shaping up to be especially severe because we have been having an extensive period of above-normal temperatures, which dries everything out.

You can learn more by clicking on the “play” icon and listening to the entire segment.

The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU 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 a podcast of “Weather with Cliff Mass” shows.

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