Monday’s hailstorm and two earlier this summer in Colorado Springs and southern El Paso County were part of what atmospheric scientists are calling an “active” but not unusual year for hail events.
“This is a more active year than normal, but convective storms in July and August are not totally out of the ordinary,” said Katja Friedrich, an associate professor in the Atmospheric and Oceanic Sciences Department at the University of Colorado at Boulder. “It is still an unfortunate event with repercussions, though, because of the damage at places like the zoo.”
Monday afternoon, hail as large as 4 inches in diameter plummeted parts of the county, the National Weather Service in Pueblo reported. The largest hail was recorded in southeast Security, while baseball- to softball-sized hail (2.75 inches or more in diameter) killed two animals, injured 21 people and forced the evacuation of about 3,400 people at the Cheyenne Mountain Zoo.
The county has seen hail of comparable and larger sizes in recent history, said weather service meteorologist John Kalina. On Aug. 9, 2004, 4.5-inch hail fell in Ramah, and on June 20, 2001, 4-inch hail was reported in Calhan, according to weather service data.
“We also can have storms that produce larger hailstones that go unreported,” said Kalina, adding that it is possible there was hail larger than 2.75 inches at the zoo.
As for the cause of this summer’s hailstorms, the weather service would have do “deep research” for more than a year before concluding anything, he said.
One culprit for the slew of storms is atmospheric blocking, said Andy Prein, a scientist with the National Center for Atmospheric Research in Boulder. During such an event, weather patterns stagnate, leading to repetitive weather for several days, even weeks.
Whether climate change is linked to increased frequency and severity of hailstorms is unclear, Friedrich and Prein said.
“Whether this is some abnormality of climate change is very hard to say right now,” Friedrich said. “For research, more years of active hailstorms would be helpful so we can go back and find any unusual patterns.”
Prein said, “From our observations of recorded hail, there are no clear trends up or down in the last 30 years. But what we know from climate science is, for one, that we expect the instability of the air to get larger, meaning we have stronger buoyancy and vertical winds.”
When the surface temperature warms, more energy exists at the ground. During the summer especially, when heat builds through the day, massive amounts of energy accumulate at the surface and eventually explode into what Coloradans know as summer afternoon thunderstorms. This happens without human-caused temperature increases or natural climate variability.
With those factors though, more heat and energy are pumped into a weather system, generating a more violent eruption, an increase in buoyancy (how easily the air can rise) and larger vertical winds (the difference in wind speeds at various altitudes), Prein said.
Because buoyancy and vertical winds are two major ingredients in hailstorms, it follows that hailstones should grow, he said.
“It’s hard to understand what is happening between climate change and a large hailstorm because there are so many ingredients acting together that are impacted by climate change in different ways,” Prein said. “To study them, we have to them occurring at the same time and location to understand how they interact and how climate change would overall affect them.”
Year-to-year variability further complicates research. Some years, like this one, see many hailstorms; others, very few. Researchers have started to find correlative and causal links between hailstorms and natural climate oscillation events such as La Niña, but they have yet to conclude how those links will or won’t change when climate change is a variable.
“We’re just starting to understand some of these processes and now have to ask what happens to them with climate change,” Prein said. ‘It’s a hard question to answer.”
Despite uncertainties about climate change, Friedrich said he was confident in the tie between what people perceive as more unprecedented storms and the increase in population along the Front Range.
“May and August have always been Colorado’s active thunderstorm period,” Friedrich said. “The amount of attention these storms are receiving right now might also have to do with the fact that so many people now live along the Front Range, so we shouldn’t forget that as a factor either.”
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