Behind waning Valley fog could be a lack of smoke. What?!

In California’s San Joaquin Valley foggy days (and nights) are becoming fewer and farther between. No lie. Though the trend’s been gradual, it’s been consistent.

On the waning Valley tule fog, San Francisco Chronicle reporter Peter Fimrite on May 22, 2014 in: “As Central Valley fog disappears, fruit, nut crops decline,” wrote: “The soupy thick tule fog that regularly blanketed the Central Valley and terrorized unsuspecting motorists during the winter has been slowly disappearing over the past three decades, a [University of California at] Berkeley study has found.”

I concur. But, what’s behind that reduction? Is it global warming, a change in land-use patterns or something else entirely?

So check this out. “[University of California, Berkeley biometeorologist Dennis Baldocchi] said records indicate the amount of fog increased in the Central Valley from the 1930s through the 1970s, and then decreased starting about the same time farmers cut down on winter burning,” wrote Fimrite also. “Smoke in the sky can help produce fog as the air cools, he said.”

Seriously?! For real?!

Retreating fog is one thing. Smoke as a contributing factor in terms of it aiding in the formation of fog in the Valley in winter, well, you decide.

So you know, I have no trouble whatsoever accepting the notion that pollution can affect weather. In fact, as reported on earlier, it is in a Nov. 25, 2013 Pacific Northwest National Laboratory (PNNL) news release that it is clearly stated: “Researchers had thought that pollution causes larger and longer-lasting storm clouds by making thunderheads draftier through a process known as convection. But atmospheric scientist Jiwen Fan and her colleagues show that pollution instead makes clouds linger by decreasing the size and increasing the lifespan of cloud and ice particles.”

A few paragraphs later PNNL news release authors Mary Beckman and Frances White further point out, “Also, pollution can decrease the daily temperature range via such clouds: High clouds left after a thunderstorm spread out across the sky and look like anvils. These clouds cool the earth during the day with their shadows but trap heat like a blanket at night. Pollution can cause clouds from late afternoon thunderstorms to last long into the night rather than dissipate, causing warmer nights.”

Now, as to the notion of there being some connection of smoke from open-field agricultural burning and fog in the Valley, I have absolutely no qualms in asserting that I believe further research and study in this area is needed. In fact, it is not unheard of for there, at times, to be high concentrations of wood-smoke spewing from area chimneys at this same time of year – in winter, though, it could very well be this too is less, that is, compared to years past. Which, begs the question: What, if any, influence does wood-smoke pouring out residential chimneys (and from other sources) have on the formation of fog in the Valley?

Smoke as a contributing factor in terms of it aiding in winter in the formation of Valley fog, on this I have to wonder if the jury is still out.


This post was last revised on Jun. 4, 2020 @ 7:28 p.m. Pacific Daylight Time.

 – Alan Kandel