Dog Days of August

Dry Grasslands on the Slopes

If you take one of the definitions in Webster’s Dictionary of dog days being a “period of stagnation or inactivity,” then we are experiencing dog days. The monotonous pattern of sun and fog defines early August. The only variation is the number of sunshine hours and overcast ones, or whether the fog is dry or drippy. A few mornings recently were drizzly enough to deposit .02 inches in my rain gauge. The fog drip beneath trees in some places keeps grass green and the soil muddy. Fog drip under ridgeline trees has been measured at more than ten inches during the summer months.

To add to the monotony of late summer is the absence of bird song. Except for a few late fledglings, nesting season with its reason for song is past. Most birds are at their most lethargic as they begin their annual feather molt. Wildflowers are a distant memory, their seeds long cast down into the dust where they wait for the first rains of late fall. Grasslands have faded from golden-brown to gray-beige. The afternoon wind hisses through the dry grass stalks.

Away from the coast in other regions, dog days are the hot, sultry part of the summer. At this season, Sirius, the dog star and the brightest star in our sky rises at the same time as the sun. Once it was believed that because of its brightness, Sirius added its heat to the sun’s heat.

Lawrence Hall of Science in fog

On our coast, the story is not sun but fog or as it’s sometimes called “coastal stratus.” No towering cumulus or endearing clumps of cirrocumulus clouds or the delicate wisps of high clouds composed of ice crystals, but flat, gray sheets of overcast that only have a certain drama when encountering various land forms around the Bay.

Harold Gilliam in his outstanding Weather of the San Francisco Bay Region is rhapsodical when he describes the way fog surges like a slow-moving surf forming falls or cascades at it spills over the Marin hills. From my perspective high in the Berkeley Hills, I see rivers of fog shouldering their way through the Golden Gate—a million tons of moisture headed my way.

The “engine” for the fog is the Pacific High which moves north with the sun in the late spring to sit heavily on the heaving seas of the Eastern Pacific. The Pacific High deflects rainstorms to the north keeping our summers dry. Winds blowing off the High from the northwest displace the warmer surface water, allowing for an upwelling of the deeper cold water. When the moisture-laden wind from the Pacific blows across the cold water, the air condenses becoming fog. Meanwhile, in the fog-free Central Valley the air heats up under the summer sun forming a low-pressure trough which pulls the fog inland. When the valley cools down, the fog recedes to the coastline, and we will have a few days of sunny weather until the cycle begins again.

Sometimes, though, foggy periods persist even when the valley cools down. Looking at the weather map on this first day of August, I see an “L” sitting off the coast. The low pressure trough is not likely to bring welcome rain, but will deepen the marine layer bringing only gray days and lower-than-average temperatures.

My lettuces love it and my potted red geraniums glow with their own light on these misty days. But there is nothing like the sun and a blue sky overhead to bring a lilt even to the faded landscape of early August.

—Phila Rogers