Thread: Iceout 2011
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Old 02-18-2011, 12:19 PM   #6
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Originally Posted by Merrymeeting View Post
CLA, what would cause the rise? Does 1 day of warm temps like we had one Monday cause enough runoff / melting to make the difference?
Corollaman is right. The shortest day of the year is the very first day of winter in December. The first day of winter marks the beginning of the sun rising higher in the sky and staying up longer.

We're now 2 months past our annual sunlight minimum and heading quickly toward the equinox (equal day and night.) The sun is pretty strong this time of year. The sun starts heating up rocks. Rocks in south-facing areas that are exposed to the sun all day long are now free of snow even while 18 inches of snow remains immediately around the rock.

The same thing is happening in the lake. Soon we'll start to see south-facing shores become ice-free, and areas around rocks and reefs also. This will happen even on below-freezing days because the sun is getting too high in the sky for ice to withstand.

It's harder to get snow to accumulate at this time of year, too. The clouds have to be thick enough, and the snowfall intense enough to overcome the more-direct sun. It will accumulate much more readily at night than in the daytime. If you have a sun-exposed driveway or porch, this is the time of year when an overnight snow of 1-2 inches doesn't even have to be shoveled if there isn't any more expected, because it'll melt quickly as soon as the sun comes out. If you get several inches of snow overnight you can shovel it away and the sun-exposed areas will be bare & dry by afternoon.

Back to the lake ice: It's past growth season now. On a few of the colder nights it will re-thicken some, but the sun is tilting the equation in favor of "weekly net loss" for the ice.
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