June 3, 2013

Powerful tornadoes killed 18 people in and around Oklahoma City last Friday, including 3 veteran storm chasers. The lead scientist killed was  meteorologist Tim Samaras, the founder of  TWISTEX (Tactical Weather Instrumented Sampling in Tornadoes Experiment), a project aimed at increasing lead times for tornado warnings. Two other chasers with Samaras also died—his son Pete Samaras and colleague Carl Young. Tim Samaras had been featured for five seasons on the Discovery Channel’s “Storm Chaser’s” program.

Storm chasers travel in vehicles with such special weather equipment as mobile Doppler radar to gather storm data. (© Byron Turk, Center for Severe Weather Research)

Storm chasers travel in specially equipped vehicles and try to get close to a tornado to study it. The men were following an EF3 tornado near El Reno, Oklahoma. (The EF stands for Enhanced Fujita Scale, named by meteorologist and storm researcher Tetsuya Theodore Fujita.) An EF3 tornado has wind speeds up to 165 miles (266 kilometers) per hour. Friday’s powerful storm suddenly turned course, and the TWISTEX team was caught in their truck, a very dangerous place to be in a tornado. High winds that night also swept along a Weather Channel vehicle for some 600 feet (180 meters), but those passengers survived.

Friday’s tornado comes less than two weeks after another huge tornado hit Oklahoma. The May 20 tornado in Moore, Oklahoma, left 24 people dead. One of the tornadoes formed on May 31 followed in the path of the twister that devastated Moore on the 20th.

Additional World Book articles:

• Tornado (Studying tornados)

• Twisted—More Terrible Tornados (a Special Report)

May 21, 2013

A tornado tore through Moore, Oklahoma, yesterday, a suburb of Oklahoma City, leaving 24 people dead, including 10 children.  The death count had been revised downward from the 51 dead initially reported. The medical examiners office believes some victims were counted twice in the early aftermath of the disaster.

Tornados are created when certain conditions are met: adequate moisture in the air; a layer of warm, moist air near the ground and a layer of cool air above; andwinds at higher elevations that differ from those at lower levels in speed, direction, or both. (© Gene & Karen Rhoden, Peter Arnold Images/photolibrary)

The U.S. National Weather Service estimated that the tornado was around ½-mile (0.8-kilometer) wide. The storm touched down at 2:56 pm and was on the ground for about 40 minutes. A preliminary report from the weather service estimated that the storm was an EF-4, indicating wind speeds of 166 to 200 miles (267 to 322 kilometers) per hour. (The EF stands for Enhanced Fujita Scale, named by meteorologist and storm researcher Tetsuya Theodore Fujita.)

The tornado in Moore picked up and carried away cars. Whole neighborhoods were leveled. Two elementary schools, directly in the tornado’s path, were flattened. Rescuers today are in a race to search through the rubble and find the dozens of children still missing.

This map of the United States shows the number of tornadoes that occur yearly in each 10,000 square miles (25,900 square kilometers) of area. (World Book map)

Oklahoma is one of the states in “Tornado Alley,” a belt that stretches across the Midwestern and Southern states that has a very high incidence of tornadoes. Moore was the site of one of the most destructive tornadoes in U.S. history. On May 3, 1999, a tornado ripped through the area, killing 42 people. That tornado was an EF-5, with the highest recorded wind speeds in history, at 302 miles (486 kilometers) per hour.

Additional World Book articles:

• Twisted—More Terrible Tornadoes (a Special Report)
• Weather 1999 (a Back in Time article)

May 16, 2013

Rescue workers are searching for survivors in a destroyed subdivision in Granbury, Texas, which was mowed down in the night by a mile-wide tornado. At least 6 people people are known to be dead and 37 others injured. A tornado flattened at least 50 houses in another subdivision a few miles southeast of Granbury. Granbury is about 35 miles (56 kilometers) southwest of the Dallas-Fort Worth metropolitan area.

The U.S. National Weather Service has confirmed that as many as 10 tornadoes swept through towns south of Fort Worth during the night.

A tornado’s winds can swirl at speeds of hundreds of miles or kilometers per hour, hurling debris in all directions. (© Gene & Karen Rhoden, Peter Arnold Images/photolibrary)

Additional World Book articles

• The Forecast: Better Weather Prediction Ahead (a special report)
• Twisted-More Terrible Tornadoes (a special report)

December 26, 2012

A powerful winter storm brought a white Christmas to the U.S. Midwest and tornadoes to the South. Little Rock, Arkansas, received 9 inches (91 centimeters) of snow, breaking a December 25 snowfall record that had stood for 86 years, and blizzard conditions hampered holiday travel in parts of Missouri, Kentucky, Illinois, Indiana, and Ohio.

The National Weather Service reported the sighting of more than 30 tornadoes in a line stretching from Texas and Louisiana to Mississippi and Alabama. Hardest hit was Mobile, Alabama, where numerous twisters and brutal, straight-line winds knocked down countless trees, blew off roofs, and left thousands of households without electric power on Christmas Day.

(Credit: © Colin McPherson, Corbis)

The storm caused the deaths of at least six people, primarily victims of car accidents on snow- and sleet-slickened highways in Arkansas and Oklahoma. One man was killed in Houston, Texas, when a tree fell on his pickup truck.

The same storm system is currently moving eastward, threatening the Carolinas. By the end of the week, it was expected to move up into the Northeast, with 12 inches (30 centimeters) of snow predicted.

Additional World Book articles:

• Weather
• The Forecast: Better Weather Prediction Ahead (a special report)
• Weather Terms—Cloudy or Clear? (a special report)

December 20, 2012

The first major snowstorm of the season in the Midwestern United States has already left at least three people dead in two states. In Utah, a woman who had attempted to walk to safety after her vehicle became stuck in the snow was found dead. Two people were killed in a snow-related car crash in Wisconsin.

Blizzard warnings were issued for 16 states. Subzero temperatures and blizzard conditions were dropping as much as 1 foot (30 centimeters) of snow from Kansas to Wisconsin, with the Rocky Mountains already blanketed. In southwestern parts of Iowa, winds as high as 53 miles (85 kilometers) per hour were being recorded, and nearly 1 foot (30 centimeters) of snow had already fallen in Des Moines, the Iowa state capital. By Thursday morning, hundreds of flights had been canceled at O’Hare International Airport in Chicago, creating problems for holiday travelers.

A blizzard is a blinding snowstorm with strong, cold winds. (© Colin McPherson, Corbis)

The National Weather Service is warning those in the path of the storm to stay off roads because of poor visibility. Tornado warnings remain in effect for parts of Louisiana, Mississippi, and Alabama, where high winds on the southern edge of the storm are peeling the roofs off buildings, toppling trucks, and downing power lines.

Additional World Book articles:

• Weather 
• The Forecast: Better Weather Prediction Ahead (a special report)
• Weather Terms— Cloudy or Clear? (a special report)

June 6, 2012

After record numbers of tornadoes wreaked widespread devastation in 2011, and above-average numbers of tornadoes marked the early months of 2012, meteorologists finally have some good news. For the first time in seven years, the month of May has passed without a single tornado fatality in the United States. The month’s numbers stand in stark contrast to those of May 2011, which recorded 178 fatalities.

Researchers at NOAA say favorable atmospheric conditions led to a smaller-than-average number of tornadoes in May 2012. (© Byron Turk, Center for Severe Weather Research)

Ordinarily, May represents peak tornado activity in the United States, with an average expectation of about 300 tornadoes, according to researchers at the National Oceanic and Atmospheric Administration (NOAA). May 2011 experienced a total of 326 tornadoes, compared with this year’s preliminary tornado count of 122 for the month. If the numbers are confirmed, the count may be the lowest for any May since 1954.

Why were skies so quiet during May? A lack of wind shear, a condition in which wind speeds and directions change rapidly over a short distance, may be one reason. Wind shear is a key ingredient for tornado formation, and abundant wind shear conditions helped lead to the 758 tornadoes that tore across the United States in April 2011. Another factor may be the jet stream, a band of fast-moving air currents at high altitudes. Typically, moist air from the Gulf of Mexico helps fuel tornadoes throughout Tornado Alley, a region that stretches across the Midwestern, Plains, and Southern states, especially Texas, Oklahoma, Kansas, Nebraska, and Iowa. In 2012, the jet stream has been farther north, leading to drier air on the southern side of the current and fewer tornadic storms.

Additional World Book articles:

• Safety (During a tornado)
• Weather 2011 (a Back in Time article)

April 16, 2012

A series of powerful thunderstorms spawned more than 120 tornadoes across the Plains states during a 24-hour period on April 14 and 15. The tornadoes were part of a weather system that crossed parts of Oklahoma, Kansas, Nebraska and Iowa. The National Weather Service confirmed that Kansas alone had 99 tornadoes on the night of April 14. In Oklahoma, at least 6 people were killed and 28 others injured in Woodward, a town 140 miles (224 kilometers) northwest of Oklahoma City. A tornado caused widespread damage in Wichita, Kansas, including the loss of electric power in parts of the city. Between 75 to 90 percent of the homes in Thurman, Iowa, were leveled, but miraculously, there were no major injuries. Outside the town, five tractor-trailers traveling on Interstate 29 were overturned by the high winds.  A tornado took the roof off the regional hospital in Creston, Iowa, a town of 7,800 people about 75 miles (120 kilometers) southwest of Des Moines.

Although the tornado season has just started in the United States, meteorologists point out that there have already been dozens of destructive twisters from Illinois to Texas. Tornadoes have killed at least 40 people in the United States so far in 2012.

A tornado's winds can swirl at speeds of hundreds of miles or kilometers per hour, hurling debris in all directions. Copyright Gene & Karen Rhoden, Peter Arnold Images/photolibrary

Additional World Book articles:

• Safety (During a tornado)
• Storm
• Fire From the Sky (a special report)
• The Forecast: Better Weather Prediction Ahead (a special report)

April 10, 2012

March 2012 was the warmest March in the United States since record keeping began in 1895, the National Oceanic and Atmospheric Administration (NOAA) announced on April 9. The first quarter of 2012–January, February, and March–was the warmest ever recorded in the continental United States (not including Alaska and Hawaii). The average temperature was 42 °F (5.5 °C), 6 degrees Fahrenheit above the long-term average. The warm temperatures contributed to conditions favorable for severe thunderstorms and tornadoes. According to NOAA’s Storm Prediction Center, more than 220 tornadoes were reported in the United States in March.

A resident surveys the wreckage of a house blown off its foundation by a tornado. Most tornado damage is severe but localized. (AP Photo)

On March 2, for example, deadly storms blew across the Midwest and South, spawning dozens of tornadoes that left 40 people dead amid the rubble of destroyed buildings and overturned vehicles. The storms touched down in 9 states, killing 21 people in Kentucky, 13 in Indiana, 4 in Ohio, and 1 each in Alabama and Georgia. According to the National Weather Service, the four tornadoes that hit Kentucky with winds of up to 160 miles (358 kilometers) per hour were the worst in the region in 24 years. In Indiana, an EF-4 tornado–the second highest rating on the Enhanced Fujita  scale–slammed Henryville with winds of 175 miles (280 kilometers) per hour, then mowed over southeastern Indiana for more than 50 miles (80 kilometers). The March 2 storms resulted in the first billion-dollar disaster of 2012.

Additional World Book articles:

• Global warming
• Weather

April 4, 2012

Rare twin supercells unleashed at least 18 tornadoes on the Dallas-Forth Worth metropolitan region. (A supercell is a massive low-pressure center characterized by a very large cumulonimbus cloud and long-lasting thunderstorm, often producing numerous and violent tornadoes.) The National Weather Service characterized the storms as among the most destructive in the area’s history. Twisters flung several massive semi-tractor trailers into the air and tossed a school bus across a road and into a diner. Hundreds of houses were severely damaged or leveled in the Dallas suburbs of Arlington, Lancaster, and Forney. In Arlington, an entire wing of a nursing home collapsed, forcing the evacuation of dozens of residents. The storms left thousands of households without electric power. Miraculously, there were no fatalities and relatively few injuries.

A supercell thunderstorm is a violent storm dominated by a single gigantic cell--a weather system made up of storm clouds and the winds associated with them. Rain and hail may fall for hours. (National Center for Atmospheric Research/University Corporation for Atmospheric Research/National Science Foundation)

At the Dallas-Ft. Worth International Airport, all flights were canceled, stranding thousands of passengers. Baseball-size hail pounded planes on the tarmac waiting for take-off. “The noise of ice . . . hitting the aluminum exterior of a 757 was as deafening as it was frightening,” noted one passenger.

Although the tornado season has just started in the United States, meteorologists point out that there have already been dozens of destructive twisters from Illinois to Texas.

Additional World Book articles:

• Safety (During a tornado)
• Storm

March 5, 2012

Deadly storms blew across the Midwest and South on March 2, spawning dozens of tornadoes that left at least 39 people dead amid the rubble of destroyed buildings and overturned vehicles. The storms touched down in at least a dozen states, killing 21 people in Kentucky, 13 in Indiana, 3 in Ohio, and 1 each in Alabama and Georgia. According to the National Weather Service, the four tornadoes that hit Kentucky with winds of up to 160 miles (358 kilometers) per hour were the worst in the region in 24 years. In Indiana, an EF-4 tornado–the second highest on the Fujita scale–slammed Henryville with winds of 175 miles (280 kilometers) per hour, then mowed over southeastern Indiana for more than 50 miles (80 kilometers).

The governors of Indiana, Kentucky, and Ohio have declared states of emergency. The Federal Emergency Management Agency (FEMA) announced that it was in contact with officials in the affected states. The administration of President Barack Obama issued a statement that the “extent of the damage may not be known for days” and “that the administration, through FEMA, is closely monitoring the storms and their impacts.”

A tornado's winds can swirl at speeds of hundreds of miles or kilometers per hour, hurling debris in all directions. The tornado appears in this photograph as a white funnel above a darker cloud of debris. © Gene & Karen Rhoden, Peter Arnold Images/photolibrary

The storms on March 2 were the second in the region in little more than 48 hours. The more-than 50 tornadoes in Kansas, Missouri, and Illinois on February 29 combined with the more-than 85 tornadoes that touched down on March 2 set yet another record for unseasonably severe weather in the region. In 2011, the United States experienced 14 natural disasters that each caused at least $1 billion in destruction, 7 of them involving tornadoes.

Additional World Book articles:

• Safety (During a tornado)
• Storm