NATURAL VIEW:Peaks and valleys in canyon weather

People who live in two-story houses often have a problem keeping the downstairs as warm as the upstairs. That’s because warm air is less dense than cooler air, so it rises.

The flip side is that cold air, being more dense, sinks. Outdoors, in our canyons, that’s what we notice.

Last weekend, we were birding at Santiago Oaks Regional Park early in the morning (OK, early for me).

Along the creek, in the bottom of the canyon, everyone was wearing a long-sleeved shirt or jacket. It was a fine fall day, with a little nip to the air.

About midmorning, we took a short, steep trail up out of the canyon and found ourselves maybe 50 feet higher, on a small hill, but suddenly thrust back into summer. It was at least 10 degrees warmer. People took off their jackets and stuffed them into backpacks.

This phenomenon occurs all over, of course, and the steeper and deeper the canyon, the more apparent it is. People living in the bottom of a canyon have cold houses, those on the slopes have warmer ones.

I lived for 25 years at the base of a north-facing slope in the Canyon Acres neighborhood. By mid-afternoon, the sun was leaving the slope, although across the canyon the south-facing slope was still in full sun. The increasing shade cooled off our side of the canyon, and the air immediately above it.

The cooler air then began to sink downhill into the canyon. Like all people living on the “cold” side of a canyon, we learned to expect the abrupt late afternoon change of temperature.

It was especially noticeable on the uphill side of our house, which blocked the downward flow of the air.

Like water, cold air piled up on that side of the house, but it was still warm on the downhill side. The weight of that dense, cold air sometimes backed up the chimneys and even scattered ashes into the room.

Warm air from a small fire struggled to escape against the column of dense cold air snaking down the chimney.

Eventually, of course, the air flowed around the house, displacing warmer air in the creek bed and pushing it out toward Laguna Canyon and, eventually, the Pacific.

It was our own mini-Santa Ana air flow, playing out daily in all the side canyons in Laguna.

Santa Ana weather is so named because rivers of air from the desert move toward the coast, flowing along the Santa Ana River bed.

Laguna Coast Wilderness Park has many small, hidden side canyons that the 1993 fire uncovered.

Today, dense brush and trees are back, and the only sign of the canyons is the stream of cold air that flows out of them. As you hike the trails on a still morning, see how many you can find.