Damage to the CNN building in downtown Atlanta, GA following a tornado on the evening of 03/14/08.

A recent study by experts on land-atmosphere interactions suggests a connection may exist between large urban population centers and the intensity of tornadoes that impact these areas.

The urban heat island effect is the term given to the hot, dry conditions generated by large expanses of buildings, asphalt, and other human-made conditions that alter the landscape otherwise covered by fields, forests, and bodies of water.  Decades of research have indicated that large urban areas reach higher temperatures during the day, stay warmer at night, and tend to have drier air surrounding them, as there is little open water or moist soil to provide atmospheric moisture.

Atlanta Tornado of 2008

The study indicates a connection between the intensity of the 2008 urban Atlanta tornado and the heat island effect suggests that the hot, dry urban conditions may have led to a larger discrepancy with the surrounding atmospheric conditions, enhancing stability and thus intensifying the storm as it approached the city.

This map published by the Atlanta National Weather Service office describes the track and intensity of the tornado that struck Atlanta, GA on 03/14/2008. Click for a high resolution image (Credit: NOAA / NWS)

The recent research has taken our understanding of the urban heat island one step further by connecting its impact to severe weather.  “Urban regions create their own weather,” said Dev Niyogi, a climatology professor at Purdue University in Indiana and the lead author of the study, which was funded by the National Aeronautics and Space Administration. “As we are becoming bigger and bigger in terms of our urban footprint, there’s a distinct probability we are going to see cities have their own weather patterns.”

However, not all meteorologists and climatologists agree.  Harold Brooks, a research meteorologist at the federal government’s National Severe Storms Laboratory, in Norman, Okla., said it is already widely accepted that wet ground breeds tornadoes, and noted that strikes on urban areas aren’t rare. There is no evidence suggesting downtown areas are hit “any less or more than any other area of the same size,” Mr. Brooks said. In the past decade, tornadoes have hit Nashville, Tenn.; Fort Worth, Texas; and Miami, as well as Atlanta, he said.

Urban Tornadoes

A tornado strikes downtown Salt Lake City, UT in 1999.

The myth that tornadoes are less likely to strike urban areas continues to remain pervasive, even in the face of evidence to the contrary.

It is a common – and definitely false myth that tornadoes do not strike downtown areas. The odds are much lower due to the small areas covered, but paths can go anywhere – including over downtown areas.  St. Louis, MO, for instance, has been struck 4 times in the last century.

It may seem tornadoes impact urban areas less frequently than rural areas simply because urban population centers cover a much smaller fraction of land area than rural areas.  As such, any given tornado is more likely to impact a rural wheat field in Kansas rather than the urban core of a city such as Wichita or Kansas City.

However, tornadoes impacting large urban areas are far from rare.  Beyond the 2008 Atlanta tornado, violent tornadoes have also impacted other large urban centers:

• Omaha, NE (F5, 03/23/1913)
• Topeka, KS (F5, 06/08/1966)
• Lubbock, TX (F5, 05/11/1970)
• Nashville, TN (F3, 04/16/1998)
• Little Rock, AR (F3, 01/21/1999)
• Salt Lake City (F2, 08/11/1999)
• Fort Worth, TX (F3, 03/28/2000)

For a more exhaustive list and details, see the table compiled by Roger Edwards and Joe Schaefer of the Storm Prediction Center on downtown tornadoes.

The home in Rogers, Minnesota where Jaymi Wendt, 10, was killed the evening of September 16, 2006 when a tornado struck the neighborhood. Credit: Startribune.com

The family of a girl who was killed the evening a tornado struck Rogers, Minnesota (Family of Minnesota Tornado Victim Suing Homebuilder), has now settled their lawsuit against the homebuilder out-of-court.  10-year-old Jaymi Wendt was killed on Sept. 16, 2006 in a neighbor’s home that collapsed during the storm. Her family blamed the death on improper construction of the home – particularly, improper installation of anchor bolts designed to keep the home attached to the foundation.  The office of Judge Deborah Hedlund confirmed that the suit was settled out of court on terms that would not be publicly disclosed.

Tim Marshall, a storm damage expert who was retained by the plaintiffs stated that this house was “the only one in the neighborhood that was pushed off its foundation and collapsed.”

Marshall also stated that “close examination revealed anchor bolts were not embedded deep enough into the concrete masonry foundation, so they were standing too tall to properly secure the nuts and washers. Other anchor bolts were missing nuts and washers needed to secure the sill plates.”

The damage, according to Marshall, was consistent with the improper installation of the sill bolts.  “The house was pushed to the north and collapsed on its walk out basement. The second story remained with vinyl siding, soffits, and roof shingles still intact. The garage doors were pushed inward and were lying on top of the vehicles that had been parked in the garage. The air conditioner and wood porch deck remained nearby. The roof of the garage flew off to the northeast and came to rest upright with shingles and roof vents still attached.”

Damage to a home in the Rogers, MN neighborhood were Jaymi Wendt was killed on September 16, 2006.

The trial of a Minnesota home builder is set to begin Monday in Minneapolis, Minnesota.  The family of a tornado victim is suing Monarch homes for negligence in the death of their daughter.  Jaymi Wendt, 10, was killed when the house she was in shifted from its foundation during the F2 tornado that struck Rogers, Minnesota on September 16, 2006.  The suit states that “the defective and negligent construction practices of Defendant and/or its subcontractors permitted the house to move off of its foundation and onto Jaymi Marie Wendt, which caused her death.”

The family of Jaymi Wendt contends that several shortcuts were made in the construction of the home.  Included in those shortcuts were the protections required to prevent damage from such winds as those seen in the September, 2006 tornado.  Lag bolts that were intended to secure the garage to the foundation, for instance, were not set deep enough into the concrete, according to the complaint.

In an attempt to verify the causation between Monarch Homes’ construction practices and the damage the home sustained, the Wendt family attorney is prepared to submit into evidence that this was the only home in the neighborhood to blow off its foundation and additionally, this home was the only one in the neighborhood constructed by Monarch.

While an initial search of the LexisNexis and WestLaw legal databases reveals little in the way of case law precedent, many legal experts contend suits such as this will continue to gain traction as victims and families search for a means of holding homebuilders accountable.  Since Hurricane Andrew devastated southern Florida in 1992, an increasing number of jurisdictions have enacted statutory codes requiring hurricane straps in new home construction in hurricane-prone areas.  Legal scholars who are tracking this case state that the outcome may set a similar trend in tornado-prone areas such as the midwest and southern plains states.

The Chanhassen, MN National Weather Service office released a full investigative report on the Rogers tornado, concluding that the tornado reached its maximum strength as an F-2 tornado (wind speeds between 113 and 157).

The study authored by meteorologists Les Lemon and Mike Umscheid reveals the minute-by-minute evolution of the once-in-a-lifetime outbreak.  As reported in the Kansas City Star (Greensburg study finds that storm contained 22 tornadoes), the storm may have contained more tornadoes than originally thought:

A large, long-lasting tornado 1.7 miles wide and measuring EF5 on the Enhanced Fujita scale virtually wiped Greensburg from the map shortly before 10 p.m. on May 4, 2007. Eleven people were killed and more than 50 others were injured.

It was one of 22 tornadoes that touched down in southern and central Kansas from the same thunderstorm complex on the night of May 4 and early morning of May 5.

That’s more tornadoes than initially thought, said Mike Umscheid, co-author of the study and the meteorologist who issued the “tornado emergency” warning that night for the Dodge City branch of the National Weather Service. A handful of small satellite tornadoes rotating around larger twisters initially went unnoticed.

In particular, a few of the tornadoes were very large and may have exceeded the previous record set by the Moore, OK tornado of May 3, 1999:

The Greensburg tornado registered at the top of the Fujita scale, with peak winds estimated at more than 200 miles an hour based on damage in downtown Greensburg.

The tornado that struck Moore, Okla., and other suburbs of Oklahoma City on May 3, 1999, was labeled perhaps the strongest tornado ever recorded.

But research shows the Greensburg tornado had EF3 or stronger damage in a track at least a mile wide — at least double the size of the Moore tornado.

As always, the tornado strength was measured by the damage path:

After destroying 95 percent of Greensburg, the tornado continued north, then curled left and looped back around, nearly striking the town a second time before lifting…

The Greensburg and Trousdale tornadoes were so intense the weather service’s radar in Dodge City detected vortex holes in them — something the radar had never done before, Umscheid said.

A vortex hole “is what you would see in the eye of a hurricane,” except it’s in a tornado, he said. They form when winds are rotating so rapidly they pull debris and even large raindrops from the storm’s center.

The Trousdale tornado’s vortex hole was about two miles in diameter — or not much smaller than the eye of Hurricane Charley, a Category 4 hurricane in 2004.

This study has also taught many meteorologists more about mesocyclones – the birthplace of tornadoes:

The outbreak featured something else researchers had never seen before: the mesocyclone — or “mother ship” cloud from which tornadoes develop — was rotating as rapidly as the tornadoes.

Typically, the mesocyclones rotate slowly. The Greensburg outbreak featured mesocyclones rotating so rapidly it was hard to tell them apart from the actual tornadoes on radar, the researchers said.

______________

More:

• Read the complete study by Lemon & Umscheid:  The Greensburg, Kansas Tornadic Storm:  A Storm of Extremes.
• Greensburg, Kansas Photographs Before and After the storm.
• View a radar loop of the entire mesocyclone.

This image, along with its inaccurate caption, appears to be going viral – reaching millions of viewers via email forwards, message boards, and websites. While the image now appears on dozens of websites with multiple, conflicting captions, the image first appeared through local media websites in Iowa on the evening of June 10th or the morning of June 11th, prior to the tornadic supercell that struck Little Sioux Iowa later on June 11th. Some of the earliest reports of this image appearing online include a posting on Mason City, Iowa’s Globe Gazette website on the morning of June 11th (direct image link). The image was also posted on Mason City’s KIMT website containing the following caption:

This picture was taken by Lori Mehmen of Orchard, IA taken in her front yard looking east of her house. Picture taken at 9:04 p.m. on June 10th, 2008.

The caption above appears to be the most credible, neither calling the feature a tornado, nor attributing this image to the Little Sioux, IA storm. Rather than a tornado, the image appears to be of a shelf cloud or other feature of a well-structured supercell thunderstorm. Whether a funnel or tornado exists cannot be discerned from this still photograph, as evidence of rotation is not clearly visible.

The image appeared on the heavily-trafficked news website Drudge Report on Friday, June 13th above several headline stories concerning the recent storms and flooding in Iowa, although it was not directly attributed to the Little Sioux, IA storm (view Drudge Report Screen Capture).

Among those falsely spreading the “Little Sioux Boy Scout Camp” attribute, CNN continues to host this image with an improper caption as part of its “citizen journalist” I-Report department; a segment of the CNN website that displays reader-submitted photographs, apparently without verification or vetting of any sort. The image was posted to their website on Friday, June 13th, 2008 with the following caption:

Posted by: Orion5243 // 1 day ago // Omaha, Nebraska. Here is a picture of the Tornado that hit the Boy Scout Camp in Western Iowa.

Although readers have already posted numerous comments regarding this image being improperly attributed to the Little Sioux, IA storm and CNN failing to properly attribute the image to the photographer, Lori Mehmen, the image still appears on their website (direct link) as of midday on Saturday, June 14th.

The National Weather Service has completed their damage survey of the Little Sioux Scout Camp tornado. Becky Griffis, a meteorologist from the National Weather Service office outside of Omaha, rated the tornado as an EF-3 on the Enhanced Fujita Scale. A fund has been set up to aid in the Little Sioux, IA relief effort.

In a news story Fake tornado picture embarrasses newsrooms, an Australian news agency admits to having publicized a “photoshopped” image of a tornado. A woman sent it to them as a joke thinking there wouldn’t be a chance it’d be aired on TV or online. She was wrong.

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