Why is the weather so extreme?
WNC researchers plot wild swings of temperature, precipitation
by Dale Neal
published March 13, 2008 12:15 am

Asheville – With a balmy winter, a deep Easter freeze, hailstorms in June, a scalding heat wave in August and a yearlong exceptional drought, 2007 in Western North Carolina saw a host of weather extremes.
But the mountains weren’t alone. Nationwide, last year saw more extreme weather than any year except 1998, according to the U.S. Climate Index. The index, which extends back to 1910, has seen a trend toward more heat waves, deep freezes, intense storms and droughts affecting more of the nation over the past five years, according to Richard Heim, a meteorologist at the National Climatic Data Center in downtown Asheville.

“As far as extremes, we’ve been really up there since the 1980s,” Heim said. Whether hot or cold, wet or dry, “we’re having more extreme weather at both ends.”
Developed in the 1990s by researchers, including current NCDC director Thomas Karl, the index is a composite of weather extremes affecting the continental United States, showing whether a heat wave or a cold snap affects wide swaths of the nation.
Last year was the 10th-warmest on record for the nation, marked by deadly wildfires in California, spring storms that sent 600 tornadoes spinning across the Great Plains and South, severe flooding in Texas and Oklahoma, and a devastating drought across North Carolina and much of the Southeast.
While the index itself isn’t a forecasting tool, those extremes could be tied to the climate change scientists charted in last year’s landmark reports from the Nobel Prize-winning Intergovernmental Panel on Climate Change. Those reports indicate that rising global temperatures could lead to more weather extremes with heavier rainstorms and perhaps more intense hurricane activity.
“Climate change is always happening, but man has reached a point where we are one of the controllers of climate change,” Heim said.
Civilizations and cultures changed along with the climate when droughts or colder temperatures in the Middle Ages disrupted agriculture and brought famine, Heim said. “A changing climate is not something you want to ignore. Decision-makers ought to be concerned.”
On the regional level, researchers at the Renaissance Computing Institute at UNC Asheville are trying to give planners more tools to work with in the event of future extreme weather, such as storms that could produce severe flooding like that along the Swannanoa and French Broad rivers in 2004.
Predicting weather is hard in the mountains, given the numerous microclimates, said Jim Fox, who heads the research group that’s part of RENCI.
“You look at Asheville, and it’s the driest part of the whole state. Down in Transylvania County is the wettest part of the state, and there’s not that much of a drive between Asheville and Brevard,” Fox said.
RENCI is using money from the state to place more rain and stream gauges around Western North Carolina to provide more local data.