Ice Damage Index
Meteorologists have devised a tornado-like scale to assess the severity of ice storms
If you’ve never experienced an ice storm, you probably imagine it’s a bit like a hailstorm. It’s not.
Ice storms form when a layer of warm air gets sandwiched between two layers of cold air above and below. Snow forms in the upper cold zone, which then melts as it falls through the warm region.
When it hits the cold ground at the surface, however, it freezes instantly on whatever it lands on — forming a solid coating of glaze ice. This ice can accumulate to a thickness of several centimetres, adding a huge amount of weight to trees, power lines or buildings.
That weight causes branches to snap, telegraph poles and electricity pylons to buckle, and — in rare cases — whole buildings to collapse. Damage from ice storms regularly shuts down entire metropolitan areas of the United States. It’s serious stuff.
In January 2009, for example, Kentucky, Arkansas and Missouri suffered enormous damage when a massive ice storm encased everything between the Ozark mountains and the Ohio valley in six centimetres of ice. More than two million people were deprived of power, while in Arkansas more than 30,000 telegraph poles were snapped in two. It took until the following summer to fully repair the damage.
Meteorologists are pretty good at predicting when an ice storm is on its way, but like many types of natural disaster they vary dramatically in intensity. Tornadoes have the enhanced Fujita scale and the TORRO scale to measure their ferocity. Hurricanes and earthquakes are rated on the Saffir-Simpson scale and the Richter scale, respectively.
Volcanoes have the volcanic explosivity index, while the Douglas Sea scale measures the height of waves on the ocean. Near-Earth comets and asteroids get put on the Torino scale, and we even have an index for nuclear accidents. One of our favourite metrics is the Waffle House index, which rates the severity of disasters based on how many fast food restaurants remain open.
But ice storms had always been left out in the cold. Until now.
A meteorologist and electric utility industry professional have developed an index for rating ice storms. It’s called the Sperry-Piltz Ice Accumulation Index, or SPIA Index, after its inventors Sidney Sperry and Steven Piltz, and classifies ice storms based on the ice amount they accumulate, their wind speeds, and the damage that they cause.
It runs from zero to five, where zero represents “minimal risk of damage to exposed utility systems” and five indicates “catastrophic damage” where “[power] outages could last several weeks”.
The scale has been tested successfully since 2009 by meteorologists in the United States, but now they’re ready to roll it out to the wider public, using it to explain to people what kind of weather they should expect when they hear an ice storm is coming.
Ten US National Weather Service forecast offices from Oklahoma to Kentucky will begin using the index in the bulletins they issue to the public, chosen due to the frequency of the ice storms in those locations.
“This index was tested from Washington state to Maryland to Maine and has been shown to be accurate,” Sperry told Wunderground. ”We forecast the January 2009 event as a level 5 storm about two to three days ahead of time.”
With any luck, the SPIA index will give people across the United States a little more warning of what to expect when an ice storm is bearing down on them — allowing to prepare more effectively, and hopefully saving some lives in the process.
