Tornado-related deaths have exceeded 110.
It's difficult to pinpoint the number of storms more precisely because, in an age of instant communication, multiple people often report the same storm.
"If we were living 100 years ago, we probably wouldn't even know that one-third of these tornadoes ever happened," Henry Margusity, senior meteorologist and severe weather expert with AccuWeather, said.
Margusity calls this the most severe weather season he's seen in 10 years of weather forecasting. Recently, an average year has seen a total of around 1,200 tornadoes, so scientists predict that 2008 could be a record-breaker.
As twisters climb in both number and ferocity, researchers are trying to find reasons for the uptick. But the short answer from scientists is that they don't really know.
A tornado is a violently rotating column of air that touches the ground, and typically forms in a severe thunderstorm. But a lengthy list of ingredients must exist for a tornado to form: low-level humidity; winds strong enough to create spin; and wind shear, or lower and upper-level winds traveling at different speeds or in different directions.
Harold Brooks, a research meteorologist at NOAA's National Severe Storms Laboratory, explains tornado formation as a three-step process: First, a tornado requires warm, moist air at low levels and cold, dry air at 10,000 to 30,000 feet. Wind direction and speed that change with increasing height cause a horizontal spinning effect. As warm air moves upward, the spinning rotates from horizontal to vertical. Rain draws the rotation downward, and friction from the ground adds force.
"Under the right conditions, the rotation can accelerate, pull inward and spin faster, like an ice skater pulling in her arms," Brooks said.
The Increasing number of twisters could be tied to La Nina, the cooling of water temperatures in the tropical Pacific Ocean. Jet streams from the southwest mean change of winds with height. Southerly winds from the Gulf of Mexico add warmth and moisture. All of these factors are fuel for tornadoes.
Some reports in the media have cited climate change as possible factor, a supposition Margusity is quick to reject.
"Don't even ask me the question about climate change," Margusity said. "This has nothing to do with global warming. It's just variability in the weather. Things happen. The weather gets wild, the weather calms down. It's just the way weather works."
Brooks too, dismisses climate change as a major factor. Changes in overall temperature seem to have little correlation with the number of tornadoes.
"Observationally, we have to deal with the fact that this year so far was a cooler year than the last several years both nationally and globally," he said. "And the tornado count's been way up."
It's possible 2008 may end up marking the deadliest twister year since scientists first developed reliable tracking methods some 60 years ago, Brooks said.. But he adds an age-old caveat: we can't predict the weather.
"Just because it's been a big year so far, that tells us nothing about what the rest of year will be like," he said. "Some years, the switch turns off, and the tornado season just ends. And some years, it's incredibly slow to begin with and then the switch turns on."