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Henry Lind's Weather Watch
by Henry Lind

Weather Watch

A Daily Gazette news blog
Weather events in our region and why they happen
 

Big ice falling

By Henry Lind
Monday, February 10, 2014

We commented a while back about the various sizes of snowflakes but this winter we have seen another good reason to keep a close eye to the sky – icicles. You guessed it – mathematicians and physicists have studied the formation of icicles, and published papers describing the results of their research in great detail.

The short story is that icicles form when the air is below freezing but the sun has enough energy to melt snow on rooftops. You’ve not doubt noticed that while during the past several weeks the mercury has stayed in the twenties, the days are getting longer and the sun is higher in the sky. The amount of energy hitting our roofs is greater than a month ago, causing more melting. We have also experienced an extended continuous snow cover, providing the ingredients for a perfect icicle growing recipe.

As the thin film of water of snowmelt is pulled by gravity down the outside of the icicle it gives off some heat to the air as it begins to freeze, and this warmer air rises toward the top of the icicle serving to create a buffer. Although small, the buffer slows the freezing process there. Thus, the water stays liquid as it drops further down the icicle until it finally refreezes at the tip – making the structure “grow” at the bottom.

In addition to the sun many homes have marginal or no insulation in the attic which allows heat to escape through the roof, causing more melting. We know this from personal experience, and the results of adding insulation are a dramatic reduction of the formation of these giant daggers. A dangerous situation is present because they have the potential to cause injury or damage when they finally do part ways with the roof. While the legal implications of who is responsible are both defined and debated, the better approach is to be mindful of the possibilities, insulate or safely remove them if they are on your property, and keep a close watch for falling objects as you walk around.

 
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