Memphis in May-hem: 105 mph microburst damage in Frayser

WOW, that was quite a storm!

Memphis Light Gas and Water reports that, at peak, 188,000 customers were without power at some point after the monstrosity hit on Saturday night, darkening large portions of Shelby County. High wind also affected portions of Tipton and DeSoto Counties.

There will be more time to recap the entire event later, but in this post I'd like to focus on one particular area of damage where the highest wind likely occurred. The damage occurred at and around the Memphis Police Department Training Academy near the intersection of Highway 51 and North Watkins in Frayser. This is where the severe storm moving southeast intersected an outflow boundary moving southwest from storms that were occurring north of the metro.

It is typical for colliding outflow boundaries in an unstable airmass to produce new storms. We see it all the time. In this case, when pre-existing storms along one outflow boundary encountered the other outflow, mayhem resulted. What would have been a more "typical" severe wind event became a more rare one when explosive development produced a very strong microburst that landed on the area in question and spread out to the east and south, pushed by storms moving at near highway speeds. It is estimated from these damage photos, particularly the swath of trees that collapsed or were uprooted in the first image below, that wind speeds were near or exceeded 100 mph. This is corroborated by radar data that indicates wind of more than 100 mph just 1000' above ground in the hardest hit areas, which was likely forced to the ground by the microburst near the MPD Training Academy.

Wind that spread out from that area across north Memphis and south into downtown and midtown was likely in the 60-80 mph range. Aerial photo and radar documentation is shown below.

Aerial photo showing the classic ground signature of a very strong microburst, with a stand of trees collapsing under the weight of approximately 100 mph wind. You'll notice they all fell in roughly the same direction. Photo taken over US 51, northeast of  North Watkins.

Another angle on the above photo, annotated to show the path of the wind as it blew from northwest to southeast, fanning out slightly from a point where the wind came crashing down from above and spreading out in the path the storm was taking.

An aerial shot of part of the MPD Training Academy showing damage to structures and uprooting of large trees.

Additional damage from overhead in the area of US 51 and North Watkins.

Another view of the same damage shown in the image above.

One more photo, taken west of the MPD Academy showing trees uprooted and additional damage.

Wind velocity data from the Terminal Doppler Weather Radar (TDWR) south of Memphis International Airport detected wind speeds greater than 100 mph just under 1,000' above the US 51/Watkins area at 10:51pm. A rush of air loaded with very heavy precipitation likely resulted in that wind being forced to the surface in the form of a microburst, causing the damage seen above. Image credit: Kevin Terry, who was thinking fast enough to archive the event as it was occurring!

Full credit and many thanks to Casey Kirby of Memphis Police Department's Air Support Division for providing the full set of aerial photos exclusively to MWN!

The National Weather Service in Memphis has posted this preliminary assessment of the storm:

I'd also like to use this venue to re-post what I wrote on Facebook Sunday night after having a chance to wrap my head around the events of the night before:

It's easy to get frustrated, but the guys and gals at MLGW are working hard on their holiday weekend to try and make your day a little brighter (literally). Personally, I greatly appreciate their hard work and sacrifice, as well as all those in public service who are working extra this weekend, even though I don't have power yet either! 

Also, shout-out to all our colleagues in the weather enterprise, from SPC to US National Weather Service Memphis Tennessee to the TV mets and others, who did a phenomenal job leading up to, during, and after "Memphis in Mayhem!" 

Finally, I owe a huge debt of gratitude to MWN intern Meteorologist Alex Herbst who covered 95% of last night's event on my, and your, behalf. Between my working weather for 901Fest, racing home to beat the storm, then promptly losing electricity and most cell coverage when it hit, without Alex being on top of things the entire time, this feed would've been largely silent. I and MWN followers alike thank you for your dedicated service, Alex. You have a bright future ahead of you, at much larger endeavors than this one! 

Everyone stay safe, be grateful, and thank a utility worker this week! And don't forget it's Memorial Day weekend - take a minute to remember those who paid the ultimate sacrifice so that we can moan and groan over our #FirstWorldProblems! 

I appreciate each and every one of you who choose to follow MWN and tell others about this service...

Thanks again to all of you who have offered your appreciation for our presence before, during, and after the storm. Those comments keep us going!  We'll have a more detailed recap in the days ahead.  Be sure to follow us on social media at the links below for regular updates following this storm and updates on current weather in the Memphis area!

Best to you all on this Memorial Day,

Erik Proseus
MWN Meteorologist

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Microbursts produce wind damage in Shelby County on Monday night

Severe thunderstorms rolled through the Memphis metro on Monday late afternoon and evening ahead of a strong cold front of Canadian origin. A pre-frontal trough plowed into a very unstable airmass featuring temperatures in the mid 90s, high dewpoints, and high total atmospheric moisture that contributed to torrential rain in some storms, even though it generally didn't last very long.

One result of the early storms that formed in the late afternoon heat were strong downbursts of wind, called microbursts, that resulted in straight-line wind damage in some areas, including trees and branches down and even some power infrastructure damage. Microbursts, or downbursts, occur when a mature thunderstorm collapses (part of the normal life cycle of a storm). When this happens, the air that is forced up in thunderstorms (updrafts) quickly falls to the ground, hits the earth, and spreads out in all directions, like ripples in a pond spreading out when a rock is tossed in. Microbursts have been known to produce a great deal of damage due to wind exceeding 100 mph! The wind that spreads out creates outflow boundaries, or gust fronts. Often if the wind is strong enough (58 mph or higher), a Severe Thunderstorm Warning will be issued for these phenomena and it's best to seek shelter when the tell-tale outflow boundary, or shelf cloud, is approaching!

Schematic of a micrburst, in which a thunderstorm downdraft hits the ground and the wind spreads out in all directions.

It is important to know that Doppler radar only senses wind moving towards or away from the radar, not side to side. So while the wind near the surface spreads out in all directions when a microburst occurs, the radar only "sees" the components of the wind moving along the radar beam - towards or away from the radar.

Two radar images from late Monday afternoon show the microbursts as they were occurring. The first image below shows the Doppler data (wind direction and speed) for a microburst between Germantown and Collierville. The NEXRAD is northwest (up and left) of this location, so the green colors are showing wind blowing towards the radar and the red colors are showing wind blowing away from the radar. In between is where the downdraft wind hit the ground, then spread out. Doppler estimates are about 45 mph in the green area and 35 mph in the red area. Therefore, the wind that was collapsing down from the thunderstorm was traveling much faster than either of those values, resulting in the most damage directly under the microburst.

Doppler velocity data indicates the presence of a microburst near Collierville on July 14 with strong NW wind over Collierville and stronger SE wind on the east side of Germantown.

The second microburst image came from the Bartlett area about 20 minutes later. Once again, the NEXRAD is northwest (up and left) of this location, so the green colors are showing wind blowing towards the radar and the red colors are showing wind blowing away from the radar. This microburst (at least at this time) was not as strong as the Collierville one, but nevertheless produced very gusty wind over the east side of Bartlett in particular.

Doppler velocity data indicates another microburst near I-40 and Sycamore View with strong southeast wind over Bartlett and NW wind heading into Cordova.

When microbursts hit the ground, wind can seemingly come from all directions or "swirl" as the air moves chaotically in that localized area. Some people report this swirling wind as a tornado, but the microburst is a very different wind phenomena from a tornado. Typically, those surveying storm damage will see a wind pattern that spreads out from a central point in the case of microbursts, which make it fairly obvious that a straight-line wind event occurred, rather than a tornado. Your tree or the power pole really doesn't care what hit it when it's laying on the ground though! It just knows it got hit by a wind it couldn't stand up to!

Do you have any questions about microbursts or other wind phenomena? Leave them in the comments and we'll be sure to answer them!

Erik Proseus
MWN Meteorologist

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Microburst causes damage in Collierville, TN on April 14, 2014

Strong straight-line thunderstorm wind, the result of a microburst, was the cause of damage observed in Collierville, TN from storms that moved across the area in the early morning hours on April 14, 2014, according to the National Weather Service in Memphis.  The wind was estimated at 70 mph and affected roughly a half-mile path that was about 100 yards wide.  Details from the NWS are below.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE MEMPHIS TN
511 PM CDT MON APR 14 2014

...NWS DAMAGE SURVEY FOR STORM DAMAGE IN COLLIERVILLE TENNESSEE...

.THUNDERSTORM WIND IN COLLIERVILLE TENNESSEE...

PEAK WIND /ESTIMATED/: 70 MPH
PATH LENGTH /STATUTE/: .5 MILES
PATH WIDTH /MAXIMUM/: 100 YARDS
FATALITIES: NONE
INJURIES: NONE

START DATE:04/14/2014
START TIME:0215 AM
START LOCATION: COLLIERVILLE TENNESSEE
START LAT/LON: 35.0540 -89.6810

END DATE: 04/14/2014
END TIME: 0218 AM
END LOCATION: COLLIERVILLE TENNESSEE
END LAT/LON: 35.0590 -89.6755

SURVEY SUMMARY:
A MICROBURST OCCURRED IN COLLIERVILLE TENNESSEE. SEVERAL HOMES HAD MINOR ROOF DAMAGE AND FENCES WERE BLOWN DOWN. THERE WAS ALSO A NUMBER OF LARGE TREE LIMBS DOWN AND FALLEN TREES.

NOTE: INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT AND PUBLICATION IN NWS STORM DATA.
$$

A microburst is a downdraft of cold air descending quickly from a collapsing thunderstorm and is a common phenomena with thunderstorms. The down-rushing air hits the ground and spreads out like a fan and can leave a great deal of destruction in it's wake. This is why we say to take precautions from Severe Thunderstorm Warnings similar to Tornado Warnings. The destroyed property doesn't care whether the wind was straight-line or rotating - objects can be lofted and blown about by either!

Microbursts are perhaps best known for being significant hazards to low-flying aircraft, such as those on approach or departure from airports. Fortunately these days sophisticated detection systems are in place at all major airports that have resulted in no major accidents in a couple of decades.

Photo of damage from MWN followers on social media:

Photo credit Chelsea Fennell

Photo credit Nick Iacobucci

Photo credit Stephanie Soper

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NWS concludes microburst produced minor wind damage in Olive Branch

On Monday night, July 30, shortly after 10pm, a small but powerful storm moved through the eastern side of Olive Branch, MS, just southeast of Memphis. As it passed over the automated sensors at Olive Branch Airport, a wind gust of 65 mph was recorded. Initially written off  (fully automated sensors are known to occasionally spew invalid readings), MemphisWeather.net nowcaster Kevin Terry decided to made a request for personal observations from people following MWN on social media in the Olive Branch area. And they came through!

Providing comments like "the wind was so strong and carrying so much grit in it it felt like pins and needles were sticking in me" and "I had to push my body against it to get back inside," it  became clear that the storm had produced more than ordinary gusts.  Probing further, the following report was received regarding the estimated wind speed: "I say close to 50mph...it was enough to blow over my overfull (sic) trash can." Then on Tuesday morning, an MWN follower said, "we lost 2 trees last night. Quite a few trees down in the neighborhood."

Reflectivity (precip - left) and velocity (wind - right) at 10:05pm on July 30, 2012.
A thunderstorm producing damaging wind is depicted.

Armed with reports of trees down and the other valuable information, we approached the NWS again about the 65 mph gust from the Olive Branch sensors. On re-examination of radar data from the NEXRAD in Millington, the NWS discovered that a microburst had descended from the storm on the east side of the town and happened to hit the official recording station for Olive Branch!  The 65 mph wind gust was determined to be accurate based on the reports and radar data and an official storm report was filed by the NWS.

MWN sincerely thanks all of you who provide feedback on what is happening in your area, particularly through our #mSpotter Twitter-spotting program.  Your reports are immediately transferred to the Memphis NWS office and help corroborate warnings, improving the quality of the information the NWS disseminates to the general public. This is just one example (another is the Germantown flooding from a few weeks ago) in which the NWS was able to verify the presence of severe weather through your first-hand accounts!  Keep it up and thanks so much!

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