ROANOKE, Va. (WFXR) — It has been nine years since a well-known derecho impacted the Midwest and Mid-Atlantic states on June 29, 2012.
According to the Storm Prediction Center, a derecho is a widespread-long-lived wind storm that produces damaging straight-line winds. It is usually associated with bands of quick-moving showers and storms. The line of storms must generate gusts greater than or equal to 58 mph and track over a path length of at least 250 miles to be considered a derecho.
The infamous 2012 Derecho began to form near Chicago during the early evening hours of Friday, June 29. The storm complex was fueled by hot and humid air in place over the Mid-Atlantic states. On average, afternoon temperatures were near 100°F and surface dewpoints were around 70°F. Several spots warmed up past the 100°F mark on June 29. Roanoke and Danville had a reported high temperature of 104°F while Lynchburg reached 103°F.
As the evening continued, the storm complex became stronger and “bowed out” as it moved toward the southeast. The derecho arrived in Virginia between 8:00 – 9:30 p.m.
The storm system produced 70 – 90 mph straight-line winds: an ASOS sensor suite recorded a peak wind gust of 81 mph in Roanoke. Numerous trees and power lines were blown down by the strong winds. Structural damage was also reported in parts of Southwest and Central Virginia.
One report sent into the NWS stated that 12 people were injured in Botetourt County after the winds damaged structures and blew off roofing. Another report said a few people were injured while attending an outdoor show in Rockbridge County. One person was injured by a fallen tree limb in Danville.
Virginia Governor Bob McDonnell declared a state of emergency after the storm.
More than one million people were without power in Virginia. Not only did the power outages impact 911 and cellular communications, but the outages came during a heatwave.
Many locations in Southwest and Central Virginia dealt with extremely hot temperatures for several days after the derecho. Average high temperatures were near 100°F for more than a week after the storm. NWS says more people died because of the heat in the days following the storm than from the derecho itself.
In total, five people died in Virginia as a direct result of the derecho, including a firefighter who was responding in the Boones Mill area.
Derechos can be difficult to forecast, which was the case with the June 2012 Derecho. Small-scale meteorological events can ultimately make a difference in whether a severe storm becomes a derecho. These small-scale events are often challenging to predict less than 12 hours in advance.
Although it can be difficult to forecast a derecho event well in advance, meteorologists generally know ahead of time when a severe weather threat is possible. Meteorologists can also look at radar signatures — such as a line of storms “bowing out” — to better identify a derecho-type event a few hours in advance.