Up on the roof

MU student's research might improve hail storm prediction

John Moon, a University of Missouri junior in atmospheric sciences, shows one of his hail pads from the roof of the Anheuser-Busch Natural Resources Building.

Moon demonstrates the size comparison of a golf ball to the indentation made on the hail pad.

Hail storms are bad news for most people. But for John Moon, a University of Missouri junior majoring in atmospheric sciences, a recent spring thunderstorm was cause for celebration. That was when his hail pads first recorded the impact of one-inch hailstones on the north edge of the MU campus.

Moon, who plans to become a broadcast meteorologist after graduation, has placed 40 of the hail pads around the university as part of a research project.

He's comparing the physical evidence of hail size and quantity documented by the hail pads to radar information recorded by three Missouri weather radar sites. The comparisons will show whether the weather radar systems have accurately detected the hail. If they haven't, weather forecasters know that they need to alter the computer algorithms used to interpret radar imagery.

This could mean more precise predictions of hail events.

Moon has installed the hail pads on the tops of dozens of buildings around the MU campus, effectively measuring any hail event that occurs over a square-mile area. While weather radar is expensive and complex, hail pads are cheap and simple; they're made from hardware-store foam and foil.

Though low-tech, they accurately record the number and size of hailstones that fall during a storm. Moon simply measures the depth and diameter of dents on the pads after the ice evidence has melted away and then consults the recorded radar track to determine whether the radar and hail pad evidence agree.

Tony Lupo, chair of the Department of Soil, Environmental and Atmospheric Sciences at MU, is impressed with Moon's research instincts and ability to put together a practical project that may yield important results. He says Moon's research data will probably be closely studied by the National Weather Service and other researchers — high praise for a student entering his third year of undergraduate study.

Hail pads are cheap and simple to make from hardware store foam with a foil overlay.

Most hailstones range from pea- to golf ball-sized but some can grow into monsters. The largest hailstone recorded in North America had a diameter of 7 inches, about the size of the volleyball shown on the right.

The effects of different sizes of hail are shown on hail pads collected from the rooftops.

Tony Lupo, chair of the MU Department of Soil, Environmental and Atmospheric Sciences, worked as Moon's adviser on the project.

Hail pads record the number and size of hailstones that fall during a storm. Golf balls used for demonstration show results on this pad.

Moon and Lupo discuss the comparison between hail pads removed from different building roofs on the MU campus.

"Columbia is in the perfect place for this research," Moon said. "We're far enough away from the three Missouri weather radar sites — Springfield, Pleasant Hill and St. Louis — for the radars to only see the tops of the storms. That's where the hail forms. The horizon blocks the lower parts of the storm from those radars, eliminating extraneous data that could affect the accuracy of the hail forecast."

Moon has always been interested in weather, frequently climbing to the roof of his house to watch storms develop. As a child, he used to stand in a creek and videotape himself giving weather reports.

He is currently a member of the Mizzou Storm Chase Team , which travels throughout the Midwest collecting valuable data about thunderstorm formation.

Ice bullets from the sky

According to the National Severe Storms Laboratory, hailstones grow when ice crystals or dust collide with super-cooled water droplets and freeze on contact.

Thunderstorms with strong updrafts keep lifting the growing hailstones to the top of the cloud where they encounter more super-cooled water. Hail falls when the updrafts can no longer support the weight of the ice.

The National Oceanic and Atmospheric Administration estimates that hail causes approximately $5 billion in agricultural, structural and other property damage each year. One April 2003 storm that hit Dallas-Ft. Worth caused almost $1.7 billion in damage.

While most hailstones range from pea size to golf ball size, some can grow into monsters. The largest hailstone recorded in North America fell in Aurora, Neb., on June 22, 2003. It had a diameter of 7 inches and weighed almost three pounds.

Hail season in the American Midwest starts in April and ends in October, with May and June being the most active months.

While most structures can't be moved or protected from hail, people and livestock can be, which is why the weather service and universities study thunderstorms to produce better forecasts and better warnings, Moon said.

Watching the bigger hail picture

In addition to the National Weather Service other researchers, Moon's results will also go to a volunteer group of storm watchers, coordinated by Colorado State University, called the Community Collaborative Rain, Hail and Snow Network.

Hundreds of such volunteers in Missouri — and thousands in the Midwest — monitor rain gauges and hail pads to track storm events and report their findings to a central database. Reports are shared with the National Weather Service, the United States Department of Agriculture, the Bureau of Land Reclamation and insurance companies.

If reported quickly enough, the hail pad data influences severe thunderstorm warnings.

This network of spotters extends into "Hail Alley," where Colorado, Nebraska and Wyoming meet — the spot east of the Rocky Mountains that sees the highest frequency of large hail. It can extend into Montana, South Dakota and Kansas, across the High Plains, and then southward through Oklahoma and north Texas.

The data is proving invaluable in mapping the duration and lengths of hail events, something that was not accurately tracked before the use of the hail pads.

In the Media

Posted: June 22, 2009
Story by: Randy Mertens
Photos by: Genevieve Howard