Kevin Myatt

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About Kevin

Kevin Myatt grew up in Arkansas to the tune of tornado sirens and the rhythm of hailstones, aspiring to be a meteorologist before his studies and career were turned to journalism instead. Though he often chases storms, he prefers living in the cooler, more tranquil weather of the Blue Ridge. He moved to Roanoke in 1999 to take a job on the copy desk of The Roanoke Times; writing headlines and editing copy is his principal work for the newspaper today.

Each May, Kevin assists Pulaski County High School / Virginia Tech meteorology instructor Dave Carroll in leading college and high school students to the Plains to observe severe weather firsthand. The accounts of many of his storm chases can be found here on the storm chasing page of his weather blog on roanoke.com.

Kevin was an editor for "Hurricanes and the Middle Atlantic States," a book written by D.C.-area weather enthusiast Rick Schwartz and published by Blue Diamond Books that documents hurricanes striking the mid-Atlantic states since colonial times.

The Weather Journal column began in 2003 and appears on Friday's Virginia section front in The Roanoke Times. The Weather Journal blog began in 2006 and follows weather day-by-day between the larger columns.

Tuesday's storm as rare as it was strong

In five years of writing regularly about weather, I have learned that the easiest way to have a certain weather event happen in this area is to write about how rare or unlikely it is.

That's what happened this week. After I pointed out a week ago that we might get only three or four supercells during the course of a year within 100 miles of Roanoke, one rolled through several counties to the south of Roanoke on Tuesday evening.

An isolated, long-lived storm produced large hail and high winds over a path from Tazewell County across the southern New River Valley and into Franklin and Henry counties.

It walked like a supercell and quacked like a supercell. And according to the National Weather Service meteorologist who followed it on radar, it was a supercell.

A supercell is a rotating storm that is discrete from other storms. Because its updrafts and downdrafts are separated and do not interfere with each other, a supercell continues longer than most other types of storms and can grow much stronger.

Compared with other types of thunderstorms, supercells are usually the most prolific producers of large hail, high winds and tornadoes.

William Perry, a meteorologist at the National Weather Service in Blacksburg, said Tuesday's storm exhibited consistent rotation in the middle levels of the atmosphere.

It was not rapid rotation nor was it close to the ground, so that just about eliminated any tornado threat. But the rotation was enough to keep the storm churning for hours by separating the storms updrafts and downdrafts.

Its updrafts constantly lifted lots of raindrops into a lower-than-usual mass of cold air aloft, resulting in both large and abundant hail. The storm's downdrafts, meanwhile, blasted out some strong winds that caused widespread damage to trees, power lines and a few homes.

Perry noted that the rotation became most apparent when it moved east of the Blue Ridge. That's when Franklin and Henry counties got hammered by hail that accumulated like snowfall.

Perry used the term "mini-supercell" to describe the storm, as the core containing the circulation was confined to a small area compared with the larger supercell storms common in the central United States.

Like many storms, Tuesday's tempest exhibited some things at times that blurred the lines of classification a little.

It developed a prominent shelf cloud, for instance, or a low-hanging mass pushing outward on its leading edge. At other times, Perry said, the radar echo developed a bow shape.

Both of these are indicative of a storm that, at least for the moment, has been overtaken by its outflow, rather than continuing to intensify on the winds being pulled into the storm. A storm becoming "outflow-dominant" is more characteristic of a multicell structure than that of a supercell.

A storm's structure type is largely determined by the direction and strength of winds vertically through the atmosphere.

A weak wind field aloft typically results in pulse storms, such as those we have all summer that go up and come down in about the same spot. A strong downdraft brings a torrent of wind, rain and sometimes hail, but also kills the storm's life source, its updraft.

Strong winds shifting with height result in supercells. Not only are the shifting winds able to get the storm to rotate, but they're also able to cut off individual storms from their neighbors, so the storms don't cluster together or form a line.

In between these extremes are multicell storms, which are caused by moderate winds that shift direction with height, or strong winds that blow in the same direction. Multicell storms involve several storms clustered close together, with new storms taking over as older ones die.

Supercells, in the later stages of their life cycle, often evolve into multicell structures known as squall lines or bow segments. On radar, they look just like what they sound like: a line or a bow. They bring a quick blast of strong winds, heavy rain and maybe hail, and then move rapidly through.

So Tuesday's storm may have been a supercell with some multicell characteristics at times, or perhaps at other times, a multicell with some supercell characteristics.

If you had your house, trees or garden damaged, you probably don't care which it was. It was one bad storm, far more ominous than most we have around here.

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