Source: USA TODAY
A half-inch of ice from a storm may not seem like much, but if the storm’s winds are strong enough, it could cause “catastrophic” damage and devastation, according to a new ice storm scale that’s being used this winter by several National Weather Service offices in the central U.S.
While tornadoes have the Fujita scale and hurricanes the Saffir-Simpson scale, the “Sperry-Piltz Ice Accumulation Index” (SPIA) uses forecast information to rate an upcoming ice storm’s impact from 0 (little impact) to 5 (catastrophic damage).
Ice storms occur when rain freezes as it hits the ground or other surfaces, such as power lines and trees. On average, about five to eight ice storms hit the U.S. each year, according to scale co-creator Sidney Sperry of the Oklahoma Association of Electric Cooperatives. Typically, the Northeast sees the most ice storms, he said.
Sperry came up with the index along with Steven Piltz, meteorologist-in-charge at the weather service in Tulsa.
The idea for the scale came years ago, according to Sperry, who said that Oklahoma seems to have been hit “by an inordinate number of ice storms” since 2000. One ice storm, in 2002, knocked down 50,000 utility poles, he said.
Sperry said his company needed such a scale to spell out the damage possibilities for ice storms as many as two to three days before they hit, which would then give utility companies, emergency managers and the public a heads-up about how bad the tree and power line damage could be and how long the outages will last.
Sperry worked with Piltz to create the scale in 2006, though its use has become more widespread only in the past couple of winters. It’s being tested at 10 weather service offices in the central U.S. this winter, up from five last winter. So far, the scale has been shown “to accurately predict the duration, intensity and damage capability of ice storms,” Sperry reported.
The SPIA predicts the projected footprint, total ice accumulation, and resulting potential damage from approaching storms. The scale is based on three factors: storm total rainfall, converted to ice accumulation; wind; and temperatures during the event.
“The scale is not just for power restoration,” Piltz said. “The emergency management community also likes it.” One key, according to Piltz, is how the wind speed is factored in: The danger from an ice storm can continue even after the precipitation stops, he said, if there’s enough accumulation and the winds are strong enough.
In fact, many deaths from an ice storm occur long after the storm has passed, due to carbon monoxide poisoning (from the use of generators), fires, and the loss of heating sources.
“The more time a utility has to prepare, the more time there is to bring in additional materials and supplies to help restore power as quickly as possible,” Sperry told the Weather Channel earlier this month.
Additionally, Sperry noted that the scale is usually given as a range, and includes the least (Category 0 or 1) to whatever might be the worst that is showing, say a Category 3, 4 or 5. “But, we seldom label an event with just the highest level being indicated, because that high level may only be in an isolated area, not the whole forecast area.”
One of the worst ice storms in North American history — one that hit 16 years ago next month — would almost certainly have been a Category 5. The ice storm killed dozens of people in the Northeast U.S. and in Canada, left property damage in the billions of dollars, damaged or destroyed millions of acres of trees, and caused millions of people to lose power for days and or weeks, according to the weather service.
Some areas picked up an incredible 3 inches of ice, the weather service reported.
More recently, a massive January 2009 ice storm in the Ozarks and Ohio Valley was correctly forecast as a Category 5 about two to three days ahead of time, Sperry said.