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01/17/07 03:39 PM: Science and History of Ice Storms

With the recent outbreak of ice storms in the United States, I thought I'd take a look at other historical storms and also address what exactly causes an ice storm.

First of all, check out this site for some of the basic meteorology behind an ice storm. From the article:

"Whether freezing rain forms from the cold rain or not depends critically on the characteristics of the surface cold air layer. If the layer is too thick or too cold, it will refreeze the rain into ice pellets (sleet). If the cold layer is too warm or too shallow, the rain will continue to the ground as normal rain and will not freeze unless the temperature of the ground or some other surface it contacts is well below freezing. Often small temporal or spatial differences in air temperature and in droplet size result in freezing rain mixed with sleet, snow or non-freezing rain.

The sensitivity of freezing rain formation to the temperature of this lower air layer makes precise forecasting of formation, amount and ice accumulation rate difficult, particularly since sites measuring the vertical temperature distribution are few and widely spread across the affected region.

In most cases of glaze formation, the temperatures of the air, the rain water, and the surface are at or slightly below 0^oC, especially in those events where icing is extensive. Glaze ice usually forms when the air temperature near the surface is in the narrow range of -4^oC to 0^oC (25^oF to 32^oF). Once the water droplet strikes a surface, the violent impact triggers a rapid transformation of the supercooled liquid water to ice."

Anyway, there's the science behind it. Now let's look at some other examples of brutal ice storms.

The first one that comes to mind is the Ice Storm of 1998. Wikipedia has a good summary of the storm that hit Quebec, Ontario, New Brunswick, New York, Vermont and New Hampshire. Damage estimates from that storm ranged from $5-7 billion, and there were nearly 60 deaths reported. Damage to Canada's power infrastructure was severe, as this picture shows:

Jumping back a bit, we also have the Great Ice Storm of 1886, which hit New Hampshire.  I point this one out since there is a good resource with historical photos online.

Here's one of the photos:

There was also the Nashville Ice Storm of 1951, also known as the "Great Blizzard." The National Weather Service has the history of that storm.

I'm sure there have been plenty of other large ice storms, and this is simply a quick summary. However, it is clear that ice storms are some of the most damaging and most dangerous storms.

My number one tip, if you're in an ice storm, no matter what kind of car you have (SUV, 4 wheel drive, etc), don't try to drive it. Stay put. Don't become a bumper car, as seen in a video shot in Portland.

Finally, you can check out this handy (albeit a bit corny) PDF from the National Weather Service: Winter Storms - The Deceptive Killers.