Thread: Iceout 2011
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Old 03-25-2011, 10:52 AM   #34
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Last weekend there was open water within 10 feet of shore at Black Cat Weather station. That water has since re-frozen, with long-term ice rather than the "overnight skim" that is common to this time of year. The re-frozen areas have gained about 0.5 inch thickness of clear ice per night, and are now 1.5 to 2 inches thick, clear ice. It's been many years since the last time this level of re-freezing happened this late in the season. The sun should be melting it, but that's not happening.

The ice didn't have much time (at the beginning of the season) to gain much clear ice (the strong stuff) before the snow hit. Snow slows down the ice growth because it's an insulator. There IS clear ice out there, with the more flaky (weaker) snow ice glued on top of it. However, the snow ice acts as an insulator against melting, from mid-February onward.

Many have last year's record-early iceout on their minds. Two major factors contributed to that.

The first was lack of snow, last winter. We got clear, solid ice last winter. But that stuff doesn't stand a chance against the sun, after about the 20th of February. It needs snow to insulate it, if it's going to last. We didn't get much snow last winter; it all went south of New England.

The second factor in last year's early iceout was wind. February and March 2010 averaged 7 and 5 mph, respectively. If an entire day averages 7 mph, we get branches down. A day averaging 5 mph will take down twigs and make it impossible to rake leaves. During February and March of last year, we had a number of high wind gusts, peaking at 60 mph at the end of February -- a critical time of the season for the ice.

This year's "iceout season" wind has been much lighter. February (last month) averaged 2 mph, and this month is averaging 3 mph. Peak gust for the period is 46 mph.

Wind weakens the ice. It tries to lift the ice up (the same force that lifts the water into waves) and when the wind lulls the ice falls back down again. You can see it in the WeatherCam's time lapse on a windy day. The repeated lifting/dropping of the ice -- a very subtle wavelike action -- weakens it by flexing. When some areas become open, the wind will stir up warmer water from below and act as a circulator.

This year we have plenty of white insulation on the ice, and it hasn't been very windy during the very "iceout-critical" Feb-March time period.

And for the past few days it's actually been cold enough to re-freeze.

Even still, the ice didn't get that thick before the snow came to slow down its growth, and April brings a much higher sun and great lengthening-of-daylight, so I'd be amazed if the ice lasted "late" this year. I'm going for an average iceout this year, which would be April 16 to 24.
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