NWS: Thursday's Severe Weather Classified as ‘Low-End' Derecho - WSET.com - ABC13

NWS: Thursday's Severe Weather Classified as ‘Low-End' Derecho

Posted:
ABC 13 viewer Wendy Mawyer Pribble from Bedford. ABC 13 viewer Wendy Mawyer Pribble from Bedford.
ABC 13 viewer Wendy Mawyer Pribble from Bedford. ABC 13 viewer Wendy Mawyer Pribble from Bedford.
This satellite picture, courtesy of the National Weather Service, shows how unorganized Thursday's system was early in the day. This satellite picture, courtesy of the National Weather Service, shows how unorganized Thursday's system was early in the day.
The same satellite picture, shown around 2:45 p.m. Thursday shows the individual storms starting to come together, forming the derecho. The same satellite picture, shown around 2:45 p.m. Thursday shows the individual storms starting to come together, forming the derecho.
Finally, the storms formed a classic derecho signature, showing up as a solid line of clouds on satellite late Thursday, once the system had moved into eastern Virginia and into North Carolina. Finally, the storms formed a classic derecho signature, showing up as a solid line of clouds on satellite late Thursday, once the system had moved into eastern Virginia and into North Carolina.

Lynchburg, VA – In the days leading up to Thursday's storm, forecasts of another derecho sent panic through social media, mainly because last June's devastating storm was still fresh on the minds of many Virginians.

It was clear to meteorologists, including the ABC 13 Weather Team, that damaging winds were possible Thursday, but a repeat of the June 29 storm didn't appear as likely.

Still, days in advance, ABC 13 alerted viewers to the potential of severe weather, focusing on the damaging wind threat. By Thursday morning, watches and then warnings were relayed to people in the storm's path over the air and through social media.

Power outages along with severe damage became evident quickly as the storms blew through Thursday.

Calling the severe weather event a derecho is a topic up for some discussion, however, according to meteorologists at the Storm Prediction Center (SPC) in Oklahoma and the National Weather Service in Blacksburg.

The Storm Prediction Center's definition of a derecho is largely based on measured wind speeds in combination with the length and size of the damage path the storms produce.

"A derecho is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms…if the wind damage swath extends more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length, the event may be classified as a derecho," the SPC says on their website.

At the National Weather Service in Blacksburg, meteorologists say names and classifications aren't as important as impacts to lives and property.

"It's very reminiscent of Sandy," NWS forecaster Mike Sporer said. "There was debate within the meteorological community about whether or not to call the storm a hurricane to raise public awareness, or call the storm extra-tropical to make it scientifically accurate."

"What matters most is the direct impact to people on the ground," Sporer added.

National Weather Service lead forecaster Jim Hudgins, one of the more experienced meteorologists at the Blacksburg office, was working the night of the June 29, 2012 derecho. He says there were notable differences in the 2012 derecho and Thursday's storm.

"The system last June had much less precipitation as outflow winds jumped well ahead of the rain in many locations when it crossed West Virginia, likely leading to a faster moving wind band, Hudgins explained of the storm last year.

The extremely hot air combined with the accelerating wind off of the mountains helped make the June 29 derecho even stronger, Hudgins said.

In contrast to last June, Thursday's system didn't really become a solid windstorm until after it moved east and south of the ABC 13 viewing area, Hudgins said.

During the June 29, 2012 derecho, the storms had already formed a continuous, sold line of damaging wind. Thursday's derecho was intense in spots, but wasn't nearly as organized as it moved through the area.

"There certainly was damage, but it wasn't as solid as last year," said Hudgins. "We had a case where individual storms were producing the major damage. If you were under one of the strong storms, you were hit hard. It made the difference between having trees knocked down, compared to just seeing a few limbs downed," Hudgins said.

"In essence, the derecho was in its beginning stages, organizing as it crossed our area," Hudgins said.

A derecho forms when the winds from several different thunderstorms join forces to produce one large gust of wind.

Hudgins said after last year's derecho and Thursday's storm, there is talk within the weather forecasting community on figuring out if different wording is needed in storm outlooks and forecasts when powerful storms are a possibility.

"There has been some talk via chat from the SPC about having a more specific definition for these events, but we will have to wait and see on that," Hudgins said.

- ABC 13 Meteorologist Jamey Singleton

Powered by WorldNow
All content © Copyright 2000 - 2014 WorldNow and WSET. All Rights Reserved.
For more information on this site, please read our Privacy Policy and Terms of Service.