In the picture you are looking at, it is Sunday morning, and you will see a thick layer of fog that has come into the valley below my house on Federal Way's eastern ridge.

During the days and nights of late winter and spring, this scene sometimes covers the entire swale from the mouth of the Duwamish through Tukwila, Kent, Auburn, Sumner and Orting all the way to_the foot of Mt. Rainier.

We call it ground or valley fog, but it is also known to meteorologists as radiation fog.

Basically a cloud in contact with the ground, radiation fog occurs when moisture from the surface of the Earth evaporates and moves upward where it cools and condenses. High pressure from the warmth of an early morning sun as it burns off the dense, moisture-laden terrain along the highest points first.

It saves the dips and troughs for last and creates scenes such as this one: an illusion of quiet fullness over an entire, bustling strip of human occupation.

I see this at least three or four times a year and I savor the suggestion of a sea of fog, like a beautiful down comforter God has gentled on the landscape.

It's not nearly as dramatic as an image of a storm-tossed ocean or a sky backed with ragged clouds before a rugged mountain backdrop. It's much mellower and subtle.

The fact that it conceals a plethora of man-made objects is what I find most appealing.

In technical terms, fog blankets like this form when the relative humidity reaches 100 percent and the air temperature drops below the dew point. It pushes the dew point lower by forcing the water vapor to condense. When this happens, fog can form suddenly, and can dissipate rapidly, depending on what side of the dew point the temperature is on.

In California's Great Central Valley, from Bakersfield to Chico, they have what they call the Tule Fog (Too-lee) and it forms every year in late winter and in the fall after a heavy rainfall.

It is named for the abundant Tule grass that grow in the wetlands in this area, and with visibility reduced to about an 1/8 of a mile, motorists there have to be particularly cautious as the accident rates soar when this pea soup settles on the highways.

But here in comfort of my living room, I can enjoy the distraction. And when this little weather anomaly happens at night, it's even more attractive. The lights of the Supermall, State Route 18 and the City of Auburn are muffled into a glow, sometimes allowing the reddish cast of the big signage of the General Cinemas to punctuate that picture, like it is enveloped in a swirl of cotton candy.

But this Sunday morning, I'll watch it decay a little more each time I get up to freshen my tea or let the dogs out or in, and each time I look out this window, I'll see more of the ridges of trees on the eastern shore, looking less and less like ancient ships murking their way to port.

The heat of the day will push further into this mattress of steam_until it's level and width shrinks from ocean to wide river, river to tributary and then the homes and buildings will return, the highway intersects and the Amtrak train blares its presence ever proudly, a signal that the day has fully begun.

You can reach Scott at Scottanthony@robinsonnews.com