Sunday, July 21, 2013

Re-visiting the summer storm of July 22, 2003 - "Hurricane Elvis"

Monday, July 22, 2013 marks the 10 year anniversary of the "Mid-South Summer Storm of 2003," or as it is now called in Bluff City lore - "Hurricane Elvis."  Like the Ice Storm of 1994 and Super Tuesday tornado that struck Hickory Hill, Hurricane Elvis is a weather event that is ingrained in the psyche of anyone who lived in the Memphis metro that summer.  In meteorological-speak, Hurricane Elvis was a "derecho" that formed from a mesoscale convective system.

A massive tree was uprooted on Belvedere Street. Photo credit Mike Maple, The Commericial Appeal.

What is a derecho?

A derecho is, in it's most basic form, a very long-lived severe wind event.  To be deemed a derecho, a severe wind event must meet stringent requirements set by Johns and Hirt (1987) and re-stated by McNeil, et al (2003) from NWS-Memphis in their report on the storm.  The requirements are:
  1. A concentrated area of thunderstorm-induced wind reports or damage resulting from wind gusts of at least 58 mph over a path of 249 statute miles (400 km)
  2. The reports in this area must exhibit a "non-random  pattern of occurrence" as a singular (serial) or multiple (progressive) swaths
  3. Within the area, there must be at least 3 reports, separated by 40 statute miles (64 km), of F1 damage on the Fujita scale or gusts of 74 mph
  4. No more than 3 hours may elapse between successive wind events
In other words, a line of thunderstorms with some damaging wind reports is NOT a derecho in and of itself.  In addition, a line of storms cannot be called a derecho until it has met ALL of the above criteria (which is not when it first forms, as some media outlets are known to do, but hours into the event).

The atmospheric setup

The environment across the Mid-South on that fateful Tuesday morning was primed to support severe thunderstorms, despite being at diurnal minimum (lowest heat content in the atmosphere, which is typically just after dawn).  At the surface, a weak stationary front was draped across the metro and had stalled, as fronts typically do in this part of the country in the summer.  Low-level moisture had pooled along and ahead of the front as surface dewpoints were in the mid 70s. The atmosphere over the metro was highly unstable for 6am (CAPE was 3400 J/kg per McNeil, et al).

Surface map at the time of the derecho showing a stationary front over the region (click for larger map)
Analysis of CAPE values at 09Z (4am CDT) indicating an extreme amount of instability for this time of day
Aloft, drier air was present in the mid levels of the atmosphere (a recipe for downbursts) and the Mid-South was positioned in a northwest flow regime. In northwest flow, winds aloft blow from northwest to southeast - a prime pattern for mesoscale convective systems (or large areas of thunderstorms) to affect the region as upper-level disturbances rode the northwest wind into the region.  An upper level trough was located to our north and northwest and the jet stream was to our north, positioning the Mid-South in a favorable environment for convection with diverging wind (a pattern in which the wind separates, or diverges, from a common point) over the area at jet stream level.  All of these were ingredients for severe weather that morning.

The mid levels of the atmosphere (500mb, or ~18,000') showing the northwest flow over the region
Jet stream level chart showing a jet streak (light blue) over the Ohio Valley and divergence over the Mid-South
Meanwhile, one of those pesky upper-level disturbances had induced thunderstorms over the Ozarks in the wee hours of Tuesday morning and they strengthened as they rode the northwest flow into the area and encountered a very unstable airmass.  As they did so, the storms, now a series of supercells with a history of producing damaging wind across northern AR, coalesced into a bow echo with strong inflow wind on the rear side of the line causing supercells to merge just across the river from Memphis.  When they merged, the inflow wind was aided by convective downbursts and hit the ground just before 7am with a force Memphians will never forget.

Radar reflectivity as the bow echo/derecho raced through Midtown, where much of the most significant damage occurred. Courtesy McNeil, et al (2003).
The storm began producing severe wind gusts over northern AR around 3am, peaked in the Memphis metro and along the TN/MS state line between 6-8am, then continued east into northwest AL and far southern middle TN from 9-10am.  Once it was all said and done, there was plenty of evidence to rate the storm not only a derecho, but likely one of the worst to ever hit Memphis.  The derecho's path length was 400 miles and it traveled this distance in a period of 7 hours - a forward speed of nearly 60 miles per hour!

Seven-hour path of the Mid-South Derecho, courtesy NWS-Memphis.
Courtesy NWS-Memphis - axis of heaviest wind damage highlighted

The immediate effects

The "Mid-South Summer Storm of 2003" caused extensive damage across the region (estimates were more than $500 million in 2003 dollars), but was concentrated in Shelby County. Other areas hit hard were northern Tunica County, DeSoto County, Fayette County, and points east along the TN/MS state line. The derecho brought torrential rain and extreme wind reports that topped out at 102 mph from a weather station at AutoZone Park and unofficially 108 mph from a barge on the Mississippi River.  Other gusts included 84 mph at WREG-TV on the riverbank south of downtown, 77 mph at the Agricenter, and 61 mph at Memphis International Airport.  One death was directly attributed to the storm (from a falling tree), while six others died in the aftermath from various related accidents, fires, and carbon monoxide poisoning.

Damage to the Gibson Guitar Factory and a leaning crane on the FedExForum construction project. Photo credit Jeremy Atherton.
In the storm's path, many trees were torn down causing the most damage by falling on houses and cars, in the streets, and most of all on power lines. More than 1.1 million cubic yards of tree debris was collected in the weeks following the storm. The wind and falling trees left more than 1,300 power poles damaged, caused 2,000 transformers to blow, and downed 76 miles of wire. At the end of the storm, some 750,000 people (~338,000 of Memphis Light Gas and Water's [MLGW] customers) had lost electricity in Shelby County alone, as 279 of their 435 circuits were knocked out. MLGW worked diligently, including doubling its workforce through contract workers, to re-build the electrical grid and restore power. Over 100,000 people were still without power after ten days and many residents had to wait as long as 16 days in the blistering summer heat to have their power restored.  The utility alone suffered $30 million in damage.

Linden Avenue looked like many other Midtown streets following the storm. Photo by Mike Maple, Commercial Appeal.
Also in Midtown, Scott McNeil of the NWS took this picture on Central Avenue.
The derecho caused 600 of the 800 traffic lights in Memphis to malfunction. Therefore resident's commutes to and from work took much longer. The powerful wind also caused a crane that was a part of the FedExForum construction project to bend, which resulted in Beale Street being shut down temporarily due to the hazardous conditions overhead. Some areas experienced flash flooding as well. For example, Idlewood Elementary had its entire cafeteria flood and ten classrooms were heavily damaged as part of its roof was blown off.  Memphis International Airport was closed for a time after the storm and President Bush declared a federal disaster area for Shelby County, clearing the way for federal assistance during the recovery effort.

In the suburbs, 80% of the Germantown area experienced power outages. Bartlett had 1,000 homes and businesses with damage. Lakeland had a total of 500 houses with damage. The Collierville area had 469 homes damaged.

Lingering effects

During the time after the storm, the crime rate rose significantly. Between July 22 and August 4, residential burglaries rose from 431 the year before to 514 in 2003. Business burglaries also rose from 113 to 218.  Because there was no power, many citizens resorted to using candles as an alternate source of light. Due to the use of candles, some fires broke out, one of which caused the death of a two month old baby.

Because it was summer in Memphis, many invested in a generator to power air conditioners and fans. Although this may have helped them cool off, carbon monoxide poisoning became a problem. In one case, ten people were found unconscious in their home and a toddler died.  Even though Memphians without power will remember sweltering conditions, records indicate that in the 16 days starting on July 22 (the period of time it took to restore all power), the average high was only 87 degrees and only 6 of those days saw a high of 90.  A couple of days did reach the mid 90s however, and overnight lows in the 70s much of that period contributed to the heat issue, as it didn't cool off enough at night to provide some even a few hours of relief on many nights.

Advance warning

The National Weather Service report (McNeil, et al) points out that, given radar systems in place at the time and the angle that the storm was coming into the county, the NWS was prevented from seeing the full magnitude of the wind velocity before the damage reports started rolling in.  However even with this limitation, a Severe Thunderstorm Warning was issued for Crittenden County at 6:15am and for Shelby County at 6:29am, about 12 minutes prior to the storm reaching downtown.  That warning, and a subsequent re-issuance, were in effect for Shelby County until 7:30am.  Warnings were also issued for counties downstream prior to the storm arriving.

A warning issued at 7:02am for DeSoto and Marshall County was the first to mention a "history of wind damage," though the magnitude of wind damage was not given.  At 7:16am, the Shelby County warning was re-issued with the wording "wind damage has been reported across Shelby County," but there was still no enhanced language indicating the extreme nature of the damage.  Three minutes later, a Fayette County warning indicated "widespread wind damage across Shelby County."  Obviously, the extent of the damage was arriving in the NWS office as the storm moved through Shelby County and efforts were made to increase the strength of the wording in subsequent warnings.

The warning process since 2003

From having personally read weather warnings and follow-up statements for the past decade, great advancements have been made in the warning process, including more use of enhanced language, regular use of severe weather statements that follow a warning with additional information on the threats posed, and certainly the 2007 transition to polygon warnings for specific areas independent of political boundaries.  In addition, new tools and radars are providing even more information and data to NWS warning forecasters.  However, there is still work to be done in this area.  We are currently in an era of modernizing the warning process even further, including the use of social scientists and surveys to determine what the best way is to get a strong message out to the public to minimize apathy and increase awareness.

A drawing created by Sher Stewart after the storm

MWN blog entries on other recent Memphis area derechos:

June 12, 2009 - Event analysis of Mid-South Derecho - June 12, 2009  and Follow-up to the June 12 Mid-South derecho
April 4, 2011 - Early April severe weather events foreshadow a busy season (Top 11 of '11, #6)
June 11, 2012 - Derecho sweeps through the Memphis metro on June 11

McNeil, S.J., et al, 2003: The Mid South Derecho - 22 July 2003. (Also, PowerPoint in PDF format)
Johns, R. H. and W. D. Hirt, 1987: Derechos: widespread convectively induced windstorms. Weather Forecasting, 2, 32-49.
Storm Prediction Center (SPC) Derecho page
SPC Page on Mid-South Summer Storm of 2003
WMC-TV special, "Destruction at Dawn", August 2003.
Commercial Appeal 10th Anniversary Retrospective
Wikipedia - Memphis Summer Storm of 2003

Erik Proseus,
MWN Meteorologist

Abigail Topham,
MWN Student Intern

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Derek Baker said...

Great article! Very informative and I hope that it is read and re-read by every meteorologist in the country that one say may have to deak with severe weather!!

Derek Baker said...

(Apologies for the typos!)