In the Fog About Our Weather This Summer? Here’s a Misty-cal Explanation From the National Weather Service

[Photo by Kym Kemp]

Does it seem to you like it’s been warmer and less foggy than usual on the coast this summer? If so, you are correct, according to Matthew Kidwell from the National Weather Service station on Woodley Island in Humboldt Bay, and he has the data to prove it.

Kidwell gestured at a graph on his computer screen. “Yes, there has been less fog and that’s what a lot of this data is,” he explained. “This is the McKinleyville airport and we’re looking at low clouds, which is clouds with a height below 1000’.”

He noted, “We obviously don’t have September’s data yet, but here’s what this year has been so far. We’ve been at 32% coverage of these low clouds. Historically you can see there’s been a few times where it’s been down around 30% for the whole summer. So it’s unusual, but not unheard of. And so then, looking at the past five years, just June through August, a lot of them were around 50% of the time, and this year it’s at 37%. So, significantly less than normal.”

Naturally, less fog means more sun. “And that’s of course brought the warm temperatures,” Kidwell said. “So for the whole summer, June through August, we’re the 6th warmest since 1897. But, 2015 was the second warmest, and ’97 was another really warm year, so we’ve had some warm years lately. Especially in August: all the top five warmest Augusts have been since 1983, and this year was the warmest August….[I]t’s been warm and sunny.”

However, he told us that more than sunshine has contributed to our warmer summer. “You probably also noticed the northerly winds haven’t been as strong. It’s been really nice and pleasant,” Kidwell continued. “The northerly winds are caused by an area of high pressure that typically sets up over the west part of the country, over the coast. It’s high pressure aloft, the northeastern Pacific high. It usually keeps all of the weather systems well to the north. It creates the hot temperatures inland, and the cooler temperatures at the coast and the northerly winds.”

Kidwell noted, “You get this air current flowing down the coast, from north to south, and then due to the Coriolis effect in the hemisphere, it curves to the right, and away from the coast.”

This drives surface ocean water west. “When the water’s flowing away, it’s gotta get refilled from somewhere, so it comes up from deeper in the ocean,” Kidwell explained. “That brings the much cooler water temperatures which keep the air temperatures cooler and can help increase the fog. So they’re all kind of tied together.”

Coastal upwelling graphic [Image from NOAA Northwest Fisheries Science Center website, Powered by ASIS]

A number of weather systems moved through the area this summer. Kidwell explained, “They’re just enough to disrupt things. There was one, the 9th and 10th of August, that was enough to bring some thunderstorms to the interior. I think we got a tenth of an inch of rain. That was about the strongest one. It doesn’t take much —they might just go by and all you could see is a few passing high clouds, and then it would clear out at the coast.”

He said, “I’m really just treating fog and low clouds as one single thing. That layer of clouds may be 500 feet thick, and the clouds are all going to be right under the inversion layer…When the inversion is up at 2000 feet, you get low clouds, but if the inversion is down at 500 feet, then the clouds are going to be right at the surface of the earth, and you’re in the fog. So when the marine layer is shallower you’re more likely to have fog versus clouds.”

Kidwell mentioned a study that looked at how fog has been declining in the redwood region since the early 20th century. “Johnstone and Dawson did this chart, and they had data from Monterey too. They did data through 2008, so at that time, they’re like, oh my gosh, the fog is definitely declining, the redwoods are in trouble. That’s what the research paper was on. But then we had this spike in fog, and we thought oh, maybe it’s not declining as much as they thought. And now it’s trending back down.”

You can check out this study on redwoods and changing fog frequency at https://www.pnas.org/content/107/10/4533.short

“There’s also other things going on,” Kidwell explained. “There’s a Pacific decadal oscillation that can change the temperatures of the water too. That is what caused a big shift in the late 70’s. And then it switched back in the early 2000’s. It’s on the span of decades. It’s really tricky to look at something that lasts for 30 years, when you only have 100 years of data.”

Is this part of a long-term trend of declining fog? Kidwell can’t say.

“It’s so hard to know when you see changes like this, whether they’re a trend or a blip,” he pointed out. “When you’re in the moment, it’s hard to see changes. And then it takes like a master’s thesis study, or a PhD study, to figure it out. That’s usually done at a university. [And] we’re mostly focused on the day to day forecasting, and then sometimes helping to put things in perspective. People ask, ‘oh, my gosh, it’s been so sunny this summer, has this ever happened before?’ And I can go back and say, well actually 1997 was kind of similar, really sunny. And yeah, August seems pretty anomalous with the temperatures, but again, we’re tied with 1983 for the warmest. So, it has happened before.”

Curious about local weather and climate? Check out the Woodley Island weather station’s newsletter at https://www.weather.gov/eka/NewsletterArchive It comes out quarterly, with reviews of recent weather events, predictions for the coming season, water year records, astronomy with tips on planetary movements, meteor showers and other interesting weather news.