In Carl Sandburg’s classic poem, the fog arrives “on little cat feet,” sits silently and moves on. But on the Northern California coast, fog doesn’t tiptoe. It billows and pounces. It sweeps over ridges and tumbles down ravines. It slithers up estuaries, rafts on the tides, trundles through the Golden Gate. And like a clueless houseguest, it overstays its welcome, lingering from Gray May through June Gloom into the month known elsewhere as August. We call it Fogust.
I used to resent the hulking thief that stole the summer skies. But after decades in its moist embrace, I’ve learned to look at fog, made of water droplets just like a cloud, from both sides — and to appreciate its unexpected gifts.
Advection fog, our local variant, forms in a dance between sky and sea. During the annual upwelling (explained further in this post), cold, nutrient-rich water rises from the deep, fueling one of the planet’s richest marine ecosystems. When warm, moist air from the Pacific meets the chilly upwelled water, it cools—and can no longer hold as much moisture.
Vapor condenses into thick, low-lying fog that hugs the shore like a woolen blanket. During what meteorologists call our summer pattern, temperatures soar in California’s sun-baked interior valleys. The warm air rises, drawing fog miles inland. That’s where it reveals its softer side.
In the hush of redwood groves, the ancient trees sustain their health—and that of the surrounding forest—by drinking water directly from the fog. Through a process called foliar uptake, their needle-like leaves absorb moisture in surprisingly copious amounts. A mature, old-growth redwood near the ocean can condense fog into eight to twelve inches of water per summer month—a third or more of its annual intake.
The redwoods share this liquid bounty with their neighbors. Fog drip, which drizzles from the canopy to the understory, can account for 40 percent of a forest’s moisture. Many plants—including sorrel, huckleberries and rhododendrons—depend on this sprinkling to endure dry spells that can extend for six months or longer.
Fog also soaks into the soil, reduces evaporation, replenishes groundwater, cools streams and rivers and helps sustain the salmon, steelhead trout and other fish that swim in them. Frogs, toads, newts and salamanders, whose porous skin must stay moist, thrive in the fog-dampened forest duff.
Wine growers—and lovers—have special reasons to toast the fog. Its wispy cloak cools vineyards during the day, retains warmth at night and reduces the need for irrigation. Its moderating effects also maintain a delicate balance of sugar and acidity in grapes, imparting a distinctive richness to Pinot Noirs and other varietals.
After months trapped under a bleak shroud, I yearn for sunlight and moonbeams. But I realize that I’d also miss this gentle gray giant. Summertime fog has declined by about a third along the Northern California coast over the past century. The likely culprits include urban heating and overall warming.
If this trend continues, the future could bring higher temperatures, drier soil, shrinking streams and rivers, more wildfires and the loss of animals and plants that depend on the fog’s wet kiss to survive. And so I wonder: In the relentlessly sunny summers that may come, will we be haunted by another Joni Mitchell lyric:
“Don’t it always seem to go
That you don’t know what you’ve got ’til it’s gone?”
Photo credits: Wikimedia Commons, Sonoma County Regional Parks
