Derecho sweeps through the Memphis metro on June 11

A mesoscale convective system (MCS)-turned-derecho swept through the Memphis metropolitan region on Monday afternoon, June 11.  Beginning as a cluster of storms in west-central Missouri, the system gained strength, feeding on very unstable air in it's path as it rounded an area of more stable air as it dove southeast into the Mid-South and then all the way to the Gulf Coast.

What is a derecho?

A derecho is a type of MCS that produces widespread severe and damaging straight-line wind.  They aren't as common as other types of MCS's and tend to feed on the warm and unstable airmasses produced during the summer months.  A derecho, by definition, must produce a swath of severe wind (58 mph or greater wind gusts) and damage over a path of at least 240 miles.  These systems last for hours and must have produced continuous damage with no breaks for more than a couple of hours.  Typically they appear as a large bow-shaped band of showers and storms.  The most cited example locally of a derecho is the "Mid-South Summer Storm of 2003," more commonly referred to simply as "Hurricane Elvis" which occurred during the morning rush hour on July 22, 2003.

June 11, 2012 Derecho

As seen in the radar animation of this particular storm system below, the derecho began over Missouri in the late morning hours.  It dropped southeast through the Mid-South around mid-afternoon, then elongated and continued unabated through the Deep South, affecting Mississippi and Alabama before falling apart as it moved over the Gulf of Mexico.  The total distance traveled was over 600 miles! As you can see, additional storms fired along the outflow of the derecho over southern Arkansas and eastern Oklahoma and Texas, which then became an MCS of it's own as it dove south over Louisiana in the wake of the derecho.

Radar animation of the long-lived derecho of 6/11/12. Courtesy UA-Huntsville.

Derecho Impacts

The impact of the derecho is clearly shown below in the graphic of severe wind reports from Monday and Monday night.  Over 300 reports of damage or measured wind of 58 mph or greater were recorded, though some were part of the additional MCS that formed over Louisiana and Texas or separate storms along the Atlantic coast.

Severe wind reports (308) from 7am Monday through 7am Tuesday as received by SPC.  

Locally, there were many reports of trees and power lines down, small outbuildings damaged or destroyed, and thousands without power in the storm's wake.  MLGW ended up with nearly 15,000 customers without power by Monday evening, though all but a couple of thousand had been restored by Tuesday morning.

Just one example of hundreds in the Memphis area - a tree down in north Bartlett

Though not producing twisting tornadic wind, wind speeds can rival weak tornadoes in these storms.  Thus, it is very important that precautions be taken during Severe Thunderstorm Warnings, at least staying indoors, away from windows, and out of harm's way.  The 60-80 mph wind that frequently accompany derechos can also topple, or severely damage, mobile homes.  If you live in one of these structures and have knowledge of an impending storm such as this one, it is always best to leave for sturdier shelter. For additional severe weather safety tips, visit the MWN Storm Center.

What was your experience from this derecho? Did you lose power and if so, for how long? Did you lose any trees or have other damage?

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