Maine is back in the deep freeze this week, with temperatures at dawn a few degrees either side of zero. Along the coast, we’re seeing a phenomenon over the waters of Penobscot Bay that often coincides with that frigid air, known locally as sea smoke.
“It’s actually called Arctic sea smoke,” explained meteorologist Ken McKinley of Rockport, owner and operator of Locus Weather, a firm that provides customized weather forecasts for mariners and others around the globe.
“It’s like a steaming cup of coffee,” he said, which is exactly what it looks like, though on a much larger scale. Tongues of steam flare up over the open waters outside harbors and coves, with some of the columns reaching up as high as 20 feet.
The cause, said McKinley, is “the really cold air flowing across the warmer water warms the air.” Water temperatures, despite the cold snaps Maine has experienced this year, remain in the 40s, significantly higher than the air temperatures.
When the air over the surface of the water is warmed—relatively speaking—it rises, now holding slightly more moisture.
“Warmer air can hold more water vapor,” he said.
But as it quickly comes into contact with the frigid air that dominates the atmosphere, it can no longer hold the water as a gas, and droplets precipitate out, visible as vapor.
“You’ll see it on really cold days over open water,” McKinley said. “If it’s too windy, you won’t see it,” and it won’t occur over ice.
Fog, technically known as steam fog, seen in the warmer months, comes when warm moist air comes in contact with the cooler surface of the water, again causing the moisture to turn back to a vapor. It’s a different process, but the same result, he said.