Driving down the JFX this morning you couldn't help but notice it. We cruised south under sunny, blue skies and mild temperatures. But as we neared downtown, the air grew suddenly colder, and the blue sky became obscured by low clouds and fog. That's the "marine layer" - a chilly layer of air, a few hundred to a few thousand feet thick, cooled and moistened by the ocean. It runs up onto the land, bringing a chill fog. Above and beyond the marine air, however, the sun is shining and temperatures are dramatically warmer. Here is what is looks like this morning from orbit. You can see the cloudy marine layer retreating across Delmarva.

At left is a nice photo of the cold, marine-layer fog from the Los Angeles Astronomical Society. And if it felt like San Francisco downtown this morning, it's no accident. The West Coast is frequently assaulted by a cool, foggy marine layer blown ashore by westerly winds. It usually retreats, or dissipates as the morning wears on. And the sky does appear to be brightening over The Sun building as I write.

Temperatures at Calvert & Centre streets fell from 70 degrees at 11 last night, to 61 degrees by 5 a.m. Then the marine layer shoved its way ashore, and the mercury dropped to 51 degrees at 8 a.m. Two hours later it's still only 53, but climbing. Deeper in the marine layer, Ocean City remains gray and 46 degrees.