a powerful summertime storm, known as a derecho, moved from Illinois to
the Mid-Atlantic states on June 29, expanding and bringing destruction
with it, NASA and other satellites provided a look at various factors
involved in the event, its progression and its aftermath.
to NOAA’s Storm Prediction Center web site, a derecho (pronounced
“deh-REY-cho”) is a widespread, long-lived wind storm that is associated
with a band of rapidly moving showers or thunderstorms. Damage from a
derecho is usually in one direction along a relatively straight track.
By definition an event is classified a derecho if the wind damage swath
extends more than 240 miles (about 400 km) and includes wind gusts of at
least 58 mph (93 km/h) or greater along most of its length.
storms are most common in the United States during the late spring and
summer, with more than three quarters occurring between April and
August. They either extend from the upper Mississippi Valley southeast
into the Ohio Valley, or from the southern Plains northeast into the
GOES-13 satellite, which watches the movement of weather systems in the
eastern half of the U.S., captured the expansion and movement of the
derecho from its birthplace in Illinois. The satellite data was compiled
and animated by the NASA GOES Project at the NASA Goddard Space Flight
Center in Greenbelt, Md.
is interesting how the process is a self-sustaining process that is fed
by a combination of atmospheric factors that all have to be in place at
the same time,” said Joe Witte, a meteorologist in Climate Change
Communication at George Mason University, Va. and a consultant to NASA
Headquarters, Washington. “That is why they are relatively rare: not all
the elements line up that often.”
said that one could think of the strong winds as a combination to two
main wind flows: the downburst winds from very high altitudes, and the
forward speed of the storms.
The AIRS images for June 30 show areas of intense convection centered off the New Jersey coast and another, less intense, system over Iowa/Indiana/Ohio. The area off the New Jersey coast is no longer a rapidly moving linear front. The near-surface atmospheric temperatures over the South and Midwest have decreased by 10 to 15 F in most areas. Credit: NASA
downburst occurs when cold air in the upper atmosphere is cooled more
by the evaporation of some of the rain and melting of the frozen
precipitation pushed up into the high levels of the towering
cumulonimbus (thunderclouds). That cold air becomes much denser than the
surrounding air and literally falls to the ground, accelerating like
any other falling body. “The huge blob of very cold air from the upper
atmosphere has a higher forward wind speed since it is high in the
atmosphere, ” Witte said. “This gives the ‘blob’ great forward momentum.
Add that speed to the falling speed and the result is a very powerful
forward moving surface wind.”
process of a derecho can become self-sustaining as hot and humid air is
forced upward by the gust front and develops more (reinforcing)
towering clouds. When one adds in a rear low level jet stream, there is
nothing to stop the repeating process.
Aqua satellite flew over the derecho on June 29 and June 30, using the
Atmospheric Infrared Sounder instrument (AIRS) onboard to capture
infrared imagery of the event.
AIRS images for June 29, shows the crescent shape of the initial stage
of the derecho as it gathered strength on the Michigan-Indiana-Ohio
border and began its rapid eastward movement. “The AIRS infrared image
shows the high near-surface atmospheric temperatures blanketing the
South and Midwestern U.S., approaching 98 F,” said Ed Olsen of the AIRS
Team at NASA’s Jet Propulsion Laboratory.
AIRS images for June 30 show areas of intense convection centered off
the New Jersey coast and another, less intense, system over
Iowa-Indiana-Ohio. The area off the New Jersey coast is no longer a
rapidly moving linear front. The near-surface atmospheric temperatures
over the South and Midwest had decreased by 10 to 15 Fahrenheit in most
areas,” Olsen said.
This photo of a downed tree was taken in Washington, D.C. The wind gusts of as much as 70 mph in the Washington area were responsible for countless downed trees and powerlines. Credit: Image copyright Kris Brown, used with permission
NASA satellite captured the before and after effects of the derecho’s
impact on the power grid from Philadelphia, Pa., to Richmond, Va.
Suomi National Polar-orbiting Partnership satellite (NPP) captured
night-time images on June 28 and June 30, that reflected the massive
blackouts that occurred after the derecho swept through the mid-Atlantic
power outages in Washington, D.C., and Baltimore were visible in NPP’s
night-time images on June 30, although clouds obscured lights from
Philadelphia and other areas north and east of Baltimore. Of particular
interest is the loss of light to the north and west of Washington along
the Interstate 270 and Interstate 66 highways and Maryland Route 267.
The images were taken with the day/night band of Suomi NPP’s Visible Infrared Imaging Radiometer Suite (VIIRS).
this event seemed more like a 100-year storm, there was a powerful
derecho event over the same states on July 4 and 5, 1980. The National
Oceanic and Atmospheric Administration (NOAA) called the event “The More
Trees Down Derecho.” States affected by that even included Iowa,
northeastern Missouri, Illinois, Indiana, Ohio, West Virginia, western
Pennsylvania, northern and eastern Virginia, and Maryland. That derecho
had wind gusts in excess of 80 mph at several points along the storm’s
path, and it took 73 lives.