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CanisLupusArctos · 01-20-2009, 08:47 PM

This morning brought a phenomenon normally seen only above treeline in the White Mountains and in similar places but it has been known to occur on the lake: Rime ice. This is what happens you have freezing fog. Yesterday evening, temperatures fell rapidly once the sky cleared out. The air quickly reached its moisture saturation point (dewpoint) at 7 degrees (cold air can't hold as much moisture as warm air) and dense fog formed. A breeze from the southeast at 2 mph made the fog move just enough so it froze to everything it hit.

I spent the night out on the lake with a couple of friends in a quincy (a type of igloo) we built. Yes, we are in our late 20s and early 30s but we are male. Around midnight we noticed the handles on our snow shovels were covered in a half-inch of rime ice whose feathers were pointing mostly to the southeast. In the beams of our LED head-lamps we could see the fog was not water droplets but crystallizing into snowflakes around us.

We awoke to find snow falling but the sky had many patches of blue overhead. Around us, and into the distance, we could see that the cloud producing the snow was actually lake fog with a cloud top at about 1,500 feet. Under the clear sky, the day's heat had spent the night escaping skyward. The resulting cold air pooled into the lake because it's a valley among hills, and cold air likes to sink. It's heavy.

The surrounding area, even the air above us, had not cooled enough to reach saturation point (dewpoint.) But the cold air had pooled on the lake surface, where the temperature continued cooling after reaching its dewpoint. Whenever that happens, the excess moisture is forced to fall (precipitate) out of the air. Usually this only happens in clouds above our heads, but this time it happened right at the ground level. We got a tenth of an inch (0.1") snow accumulation from it. The trees on the shorelines were beautiful and frosty covered with the rime feathers this morning.

01-20-2009, 08:47 PM	#1
CanisLupusArctos Senior Member Join Date: Jan 2007 Location: Center Harbor Posts: 1,049 Thanks: 15 Thanked 472 Times in 107 Posts	Rime Ice / Freezing Fog at the Lake This morning brought a phenomenon normally seen only above treeline in the White Mountains and in similar places but it has been known to occur on the lake: Rime ice. This is what happens you have freezing fog. Yesterday evening, temperatures fell rapidly once the sky cleared out. The air quickly reached its moisture saturation point (dewpoint) at 7 degrees (cold air can't hold as much moisture as warm air) and dense fog formed. A breeze from the southeast at 2 mph made the fog move just enough so it froze to everything it hit. I spent the night out on the lake with a couple of friends in a quincy (a type of igloo) we built. Yes, we are in our late 20s and early 30s but we are male. Around midnight we noticed the handles on our snow shovels were covered in a half-inch of rime ice whose feathers were pointing mostly to the southeast. In the beams of our LED head-lamps we could see the fog was not water droplets but crystallizing into snowflakes around us. We awoke to find snow falling but the sky had many patches of blue overhead. Around us, and into the distance, we could see that the cloud producing the snow was actually lake fog with a cloud top at about 1,500 feet. Under the clear sky, the day's heat had spent the night escaping skyward. The resulting cold air pooled into the lake because it's a valley among hills, and cold air likes to sink. It's heavy. The surrounding area, even the air above us, had not cooled enough to reach saturation point (dewpoint.) But the cold air had pooled on the lake surface, where the temperature continued cooling after reaching its dewpoint. Whenever that happens, the excess moisture is forced to fall (precipitate) out of the air. Usually this only happens in clouds above our heads, but this time it happened right at the ground level. We got a tenth of an inch (0.1") snow accumulation from it. The trees on the shorelines were beautiful and frosty covered with the rime feathers this morning.