Kevin Myatt

Latest entries from the Weather Journal blog

• Weather Journal remains on break
• Coastal low prompts Southwest Virginia flooding
• Hurricane Ida: Something extraordinary may be happening

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.

Bonnie hammered Danville harder than Florida coast

Two significant weather events that occurred late last week will forever be lost in the shadow of powerful Hurricane Charley. One was Tropical Storm Bonnie; the other was a massive cool air mass that rewrote the August temperature record book from the Canadian border to the Gulf of Mexico.

Bonnie will not be inducted into any tropical weather hall of fame: Bonnie was just breezy showers when it came ashore near Appalachicola, Fla., on Thursday. But the tropical storm did conspire with the advance of Canadian air to spawn tornadoes in North Carolina and Southside Virginia.

Danville was hit by a tornado late Thursday afternoon that rated F1 on the Fujita scale, according to a National Weather Service on-site analysis conducted the next day by meteorologists Hendricus Lulofs and William Perry of the Blacksburg office. The weather service's Doppler radar had indicated spin in the thunderstorm before the tornado touched down, and a tornado warning was in effect for Danville before it hit.

An F1 tornado, the second weakest category on the Fujita scale, contains winds of 93 to 112 mph. This tornado landed right in Danville's commercial district, ripping roofs off department stores and restaurants and felling trees and power lines across busy streets. It made a mess, but fortunately, killed no one. However, another tornado that hit on Friday morning killed three people at Rocky Point, N.C.

A common attribute of tropical storms and hurricanes is that they spawn tornadoes during and after landfall. Big spin begets little spin. As the large fluid motion of a hurricane encounters the friction of land, the big spin breaks down into smaller areas of spin. Ultimately, this is the process that kills the storm, but it can spin off twisters before it does.

A zone northeast of the tropical cyclone's center is the most common area for tornado development. This is where the strongest squalls and thunderstorms tend to develop, as moisture is pulled out of the Gulf of Mexico and Atlantic Ocean in front of the storm.

Another important factor is that the counterclockwise winds at the surface are usually blowing at a different direction than winds high in the atmosphere. This is called "shear" and it can cause rotation in a column of air. Imagine taking a baseball bat and moving your hands in opposite directions. The bat spins. When this spin translates to the surface, a tornado is born.

True to form, the tornadoes in Danville and in eastern North Carolina were both northeast of the weakening center of what was then tropical depression Bonnie.

Tornadoes spawned by hurricanes and tropical storms are usually weaker and much shorter lived the supercell thunderstorm-driven tornadoes of the Great Plains. Winds aloft are much stronger in Midwestern outbreaks -- strong winds aloft actually deter tropical storm and hurricane development. Also, there are no great differences in temperature or humidity amid tropical systems to keep tornadoes going, like with the cold fronts and dry lines that signify supercell development.

Last week's tornadoes in Virginia and the Carolinas had one component similar to Midwestern severe weather outbreaks. A strong cold front, the leading edge of the record cool air mass I mentioned, was being forced into the muggy, tropical air mass on the East Coast. So Bonnie's spin was compounded by a clash of air masses more like April than August.

The pattern is still more April than August. Another strong push of atypically cool, dry air is set to push into the temporarily warm, humid air mass that's settled in. That promises a threat of strong thunderstorms and heavy rain this weekend -- but without any assistance from anything that has a name.