Hurricane Katrina – 10 Years Later

Incredible aerial shot of the flooding in New Orleans after Katrina.  Source: US Coast Guard

Incredible aerial shot of the flooding in New Orleans after Katrina.
Source: US Coast Guard

I vividly remember the horrible, sick feeling I got as I watched Hurricane Katrina take aim at the Gulf Coast ten years ago. It was like watching a train wreck in slow motion. You knew lots of people were going to die and there was nothing you could do to stop it. It’s a horrible, helpless feeling. Watching the news coverage of the devastation was incredibly surreal. It reminded me of how I felt on 9/11. You feel almost detached, almost as if your mind refuses to believe what your eyes are seeing. “This can’t possibly be happening,” but it is. I’ve often said meteorology is a very humbling field. As meteorologists, we try very hard to see these things coming, but no matter how good technology gets, we can only do our best to predict and understand these events…we can’t stop them. Nature and its fury never fail to remind us of our humanity and our mortality.

A map of the original French settlement at New Orleans, centered on the modern-day French Quarter.  Source: US Census Bureau

A map of the original French settlement at New Orleans, centered on the modern-day French Quarter.
Source: US Census Bureau

Scientists had been warning for years that New Orleans was at serious risk for a major disaster. The handwriting was arguably on the wall. The city was founded in 1718 by French colonists. It was a strategic location along the Mississippi River and was in fact on comparatively high ground compared to the surrounding area. It’s worth pointing out that the elevated area in and around the French Quarter, which was originally the primary settlement, escaped the worst of the flooding in Katrina and sustained relatively little damage. The city’s first major storm hit in 1722, when the Mississippi River rose eight feet and numerous buildings were destroyed. At the time, Biloxi, Mississippi was the capital of France’s Louisiana colony but there was a push to move it to New Orleans because of its strategic location and its rise as a port of importance. The destruction of the hurricane of 1722 led to serious fears about the city’s future and there was significant opposition to the move. Nevertheless, the capital was moved to New Orleans just two years later.

Explorer and astronomer William Dunbar made revolutionary observations during the hurricanes of 1779 and 1780 in New Orleans.

Explorer and astronomer William Dunbar made revolutionary observations during the hurricanes of 1779 and 1780 in New Orleans.

In 1779, 190 years to the day before Hurricane Camille obliterated the Mississippi coast, another significant hurricane struck New Orleans. Louisiana had come under Spanish rule 17 years earlier and Spain had just declared war on Britain. An entire fleet of Spanish ships (save for one) was sunk offshore and numerous ships in New Orleans harbor were thrown well inland. Numerous buildings were leveled, but the city escaped widespread flooding. Scottish explorer and astronomer William Dunbar made a groundbreaking discovery during this storm, correctly theorizing that a hurricane was an independent, progressive-moving storm that rotated around a central vortex. It took a while before this theory was accepted by mainstream science, but Dunbar’s observations proved to be a pioneering meteorological discovery. Another, even worse hurricane hit the following year, sinking every ship on area waters and leveling much of the city. During that storm, Dunbar first observed that hurricanes can produce tornadoes and that such tornadoes tend to be short lived. Just eight years later, much of the city would be destroyed by fire.

A modern reconstruction of the track of the 1812 hurricane based on historical observations. Source: Mock et. al. (2010)

A modern reconstruction of the track of the 1812 hurricane based on historical observations.
Source: Mock et. al. (2010)

In 1812, as the eponymous War of 1812 was getting started, an estimated Category 3 hurricane slammed into the delta southeast of New Orleans. Up to 15 feet of water flooded parts of New Orleans and adjacent Plaquemines Parish (where 45 people drowned). However, the 1812 hurricane was much smaller and weaker than Katrina, and rising sea levels and erosion of the delta have greatly increased the danger to the city. In 1831, a powerful hurricane struck central Louisiana, wiping out the village of Barataria south of New Orleans. Lake Pontchartrain burst its banks and flooded northern sections of New Orleans proper. 260 people were killed in the state, 150 in Barataria alone. Six years later, a Category 2 hurricane dubbed “Racer’s Storm” raked the southern Louisiana bayous on an almost west-to-east path. An eight-foot surge into Lake Pontchartrain caused 1-2 feet of water to flood most of New Orleans. Damage in the city was extensive in places, but not major.

The Bruning Grocery store near the shore of Lake Pontchartrain inundated by four feet of water following the 1909 hurricane.  Source: New Orleans Daily Picayune

The Bruning Grocery store near the shore of Lake Pontchartrain inundated by four feet of water following the 1909 hurricane.
Source: New Orleans Daily Picayune

New Orleans largely escaped the devastating 1856 hurricane that wiped out the resort island of Isle Derniere (Last Island), 75 miles southwest of New Orleans, and killed 400 people. The city again escaped when the state’s worst hurricane in history devastated the bayous of Jefferson and Plaquemines Parishes south of the city in early October, 1893. Several towns were completely wiped out. The village of Chenier Caminada was particularly hard hit, with 779 of its 1,500 residents being killed. In 1909, the city wasn’t so lucky. On September 20, a Category 3 roared over the bayous of Terrebonne Parish southwest of the city. The hurricane devastated rural communities across coastal Terrebonne Parish, where 200 people were killed. Grand Isle has been mistakenly reported to have been destroyed by this hurricane. Storm surge flooding of up to two feet was reported on the island but damage was minor. Lakes around New Orleans burst their banks, flooding the city. The city’s low-lying west side saw the worst of it, with some areas flooded in up to ten feet of water. At the time, however, those areas weren’t heavily developed. That combined with timely warnings (forecasts ahead of this storm were exceptionally good for that day and age) prevented a more devastating human catastrophe. 353 people died in the hurricane in Louisiana.

Wind damage from the 1915 hurricane was severe.

Wind damage from the 1915 hurricane was severe.

In 1915, the city was hit again. A strong Category 3 not much weaker than Katrina slammed into the southern coast west of Grand Isle on September 29. Plaquemines Parish was devastated. Over 200 people died in the parish, many of whom were never found, and miles of levees were wiped out. In Lafourche Parish, the town of Leeville was leveled and surrounding areas also suffered major damage. A 13 foot storm surge rushed into Lake Pontchartrain and caused parts of New Orleans to flood. It wasn’t as bad as the 1909 storm. The worst of it was in the Mid-City neighborhood after pumps failed. Worse flooding occurred east of New Orleans in St. Bernard Parish. However, the city was rocked by winds that gusted up to 98 mph, causing widespread major wind damage.

Moissant Airport was underwater after the 1947 hurricane.  Source: US Army Corps of Engineers

Moissant Airport was underwater after the 1947 hurricane.
Source: US Army Corps of Engineers

After that, things got quiet. The city grew and developed, with residential neighborhoods sprawling down off the high ground and into the flood plains surrounding the old city. After the 1915 hurricane, the levees were strengthened and no more floods came. Residents of New Orleans had faith that the levees would hold. The first warning came in 1947. After striking south Florida as a Category 4, a Category 2 hurricane plowed into Black Bay southeast of New Orleans. Low-lying areas of the city suffered relatively minor but widespread flooding. Moissant Airport on the shore of Lake Pontchartrain was under two feet of water. The warning was heeded and again the levees were strengthened, this time with help from Congress. The lakeshore levee and the Orleans Seawall were both increased in height and a new eight foot levee was built along the Jefferson Parish lakeshore. But it wasn’t enough.

This spectacular aerial view of the Lower Ninth Ward after Betsy bears a chilling resemblance to the aftermath of Katrina.  Source: Lyndon B. Johnson Presidential Library

This spectacular aerial view of the Lower Ninth Ward after Betsy bears a chilling resemblance to the aftermath of Katrina.
Source: Lyndon B. Johnson Presidential Library

The most terrifying foreshadowing came in 1965. Hurricane Betsy slammed into southeastern Louisiana as a strong Category 4 on September 10. A ten foot storm surge rushed into Lake Pontchartrain, causing the lake and the city’s deepwater canal (called the Mississippi River Gulf Outlet) to burst their banks. Levees along the Outlet and the Industrial Canal failed and large sections of the Ninth Ward and Gentilly were inundated…exactly what happened during Katrina 40 years later. On the south side, the Mississippi River rose over ten feet, causing additional flooding. New Orleans Mayor Vic Schiro was widely hailed for his actions in preparation for Betsy as well as during relief efforts that helped prevent an even more devastating disaster. In the aftermath of Betsy, the levees were heavily renovated by the Army Corps of Engineers. The levees were rebuilt of a stronger material and up to twelve feet higher. They were also expanded in many areas. The Corps had planned to build a large hurricane barrier on the south side of Lake Pontchartrain as an extra measure of protection for the city, but they were sued by an environmental group concerned about preserving area wetlands. To avoid a protracted legal battle, the Corps scrapped the project. It was a decision that would haunt them.

This graphic shows how the storm surge caused the levees and floodwalls in New Orleans to fail.  Source: Tulane University

This graphic shows how the storm surge caused the levees and floodwalls in New Orleans to fail.
Source: Tulane University

The reinforcements made after Betsy were in line with the available technology at the time but did not account for the exacerbating effects of a slow-moving storm. Betsy was powerful but moved very quickly. Surge is less driven by the force of the winds and more by the size of the storm, speed of motion, direction to the coast, and the shape of the coastline. This destructive potential was made abundantly clear by Hurricane Georges in 1998, which despite being only a Category 2 and hitting east of New Orleans in Mississippi (keeping the city on the storm’s weaker west side), floodwaters nearly overtopped the levees in places.

In 2001, FEMA commissioned a number of studies on hypothetical disasters, among them a terrorist attack in New York City and a hurricane disaster in New Orleans. The idea of the hurricane barrier was revisited, but the cost was considered prohibitive and the belief was that it would take a 500-year event to breach the existing levee system. Whenever there is a major disaster, it’s always easy to look back and see the warning signs and what we should or should not have done. Hindsight, as they say, is 20-20. FEMA’s greatest failing was most likely its philosophy of reactivity versus proactivity. There wasn’t a system in place for responding to 500-year events or enough emphasis on coordination between local governments and the federal government. However oftentimes our harshest lessons are also the most valuable.

The hard lessons from Katrina prepared us for the havoc unleashed by Sandy.  Source: Daily Mail (UK)

The hard lessons from Katrina prepared us for the havoc unleashed by Sandy.
Source: Daily Mail (UK)

In the years after Katrina we applied those lessons and in October of 2012, those changes were put to the test. Hurricane Sandy was an unprecedented event. Meteorologists who’d been in the business for 50 years had never seen anything like it. Like New Orleans, scientists had been warning for years about the dangers of a hurricane impacting New York City and the Jersey Shore. NYC sits at the peak of a concave coastline, which acts to greatly enhance the storm surge by focusing it on a single point. And there you have tens of millions of people all crammed together on low-lying, flood-prone coastline. It was a worst-case scenario. The Jersey Shore was devastated and New York City saw unprecedented flooding, with damage estimated at $68 billion, making it the second costliest hurricane in history behind Katrina. The death toll in the US was 157, which to me is a borderline miraculous number. I don’t think people appreciate just how easily that number could’ve been in the thousands. Outstanding local leadership and governmental cooperation saved untold lives. I think a lot of that can be attributed to the fundamental changes made in the wake of Katrina. Sandy was a beautiful example of hard lessons beautifully applied to prevent another cataclysm. The material damage was great, but most people lived to pick up the pieces. Things can be replaced, lives can’t. And at the end of the day, that’s one of meteorologists’ greatest responsibilities: keeping people safe from the worst nature has to offer.

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Meteorology’s Magic 8-Ball

The Farmers' Almanac was first published in 1792, with articles and predictions for 1793. Credit: Old Farmers' Almanac

The Farmers’ Almanac was first published in 1792, with articles and predictions for 1793.
Credit: Old Farmers’ Almanac

When I was a kid, and a blossoming weather nerd, I used to love reading the Farmers’ Almanac. They always had these cool little tidbits about past weather events and I was always amazed at how they projected tides and moon phases and things like that a year in advance. However, I never paid much attention to their wild weather predictions, as fun as they were. Whenever their predictions panned out though, it always felt like magic. The truth is, however, that there was little science behind this magic. The Farmer’s Almanac is a vestige of a time when meteorology was in its infancy. When the Farmers’ Almanac was first published in 1792 (a competing publication with the same name was published in 1818), we understood very little about how weather worked. In the 19th Century, astrology was quite popular and a common theory was that weather could be predicted well in advance by studying the alignment of planets, the Moon, and the stars.

Stephen Saxby's prediction of the hurricane that hit New England in 1869 earned him much acclaim but they were based on flawed astrological principles. Credit: Albert County Museum

Stephen Saxby’s prediction of the hurricane that hit New England in 1869 earned him much acclaim but they were based on flawed astrological principles.
Credit: Albert County Museum

On Christmas Day, 1868, British Royal Navy lieutenant and amateur astronomer Stephen Saxby submitted a letter to the editor of the London Evening Standard, predicting severe high tides in the North Atlantic on October 5 of the following year. Nine months later, on September 16, 1869, Saxby submitted another letter, this time warning of an “atmospheric disturbance” between October 5th and 7th at an undetermined location. Lo and behold, on the evening of October 4, a Category 2 hurricane clobbered New England, killing more than a hundred people. Saxby received considerable acclaim for his predictions, and it seemed to vindicate proponents of the theory that the alignment of celestial bodies affected the weather. It was one of the first successful forecasts, but based on flawed principles.

Before modern meteorology, people had to live with the fear that they could be struck with terrible devastation virtually without warning.

Before modern meteorology, people had to live with the fear that they could be struck with terrible devastation virtually without warning.

Saxby’s ideas were not as outlandish as you may think and it was the source of intense debate at the time. Even in the 19th Century, science had known for centuries that the moon affected the tides. Also, solar activity has now been found to have a major effect on climate. So the belief among many scientists at the time that the answer to our weather lay in outer space was not a farfetched one. Now we know better, and even then Saxby’s ideas were met with substantial criticism, but in the 19th Century, scientists didn’t have a lot to go on. There were no satellites or radar or even airplanes. The only warning came when some other poor sap got hit without warning, be it on land or a ship at sea, and hopefully survived to get the word out to places that might be in its path. This uncertainty understandably led to a lot of fear and people looked desperately for someone to find the answer to the great biblical mystery that was weather and its terrible “Acts of God”. That’s where publications like the Farmers’ Almanac came in. Every year, they came out with predictions based on secret knowledge that at least seemed to get it right a lot. This perception probably had more to do with people being so amazed with the successful predictions that they forgot about the not-so-successful ones, than it did with good science.

The US Weather Bureau, the precursor to the National Weather Service, was founded in 1870 and began regularly producing weather maps, which debuted in the 1860's. They were part of the wave of scientific innovations in the field of meteorology that took place in the latter half of the 19th Century. Credit: NWS

The US Weather Bureau, the precursor to the National Weather Service, was founded in 1870 and began regularly producing weather maps, which debuted in the 1860’s. They were part of the wave of scientific innovations in the field of meteorology that took place in the latter half of the 19th Century.
Credit: NWS

But times have changed. Modern technology has allowed meteorology to step out of the realm of mysticism and into real science. Weather radar was born out of the aftermath of World War II and he first weather satellite, TIROS I, was launched in 1960. Innovations such as these revolutionized the field of meteorology and enabled drastically improved forecasts. Also, the 1960’s saw an increase in climatological and statistical research and improvements in modeling. The first forecasting model came out in 1955 and was very primitive by today’s standards but it was a dramatic improvement over what really amounted to educated guesswork. Improved models began to be introduced in the 1970’s. The fear and the uncertainty that the Farmers’ Almanac assuaged began to ebb. The publication has now become more of an amusing oddity than an impactful weather publication, and while its ability to attract young people such as my younger self to weather is admirable, it no longer has the public influence it once did. It has become the magic 8-ball of meteorology. It’s fun to shake it and see what it says about the future, but it would be foolish to take any of it seriously. Reading the Farmers’ Almanac is a bit like reading your horoscope in that as unsubstantiated as the science is, it does raise awareness of things that could potentially happen and may make people pay more attention to real forecasts. That’s what I hope anyway.

I think the Farmers’ Almanac has hung on largely because long-range forecasting remains an area where skill is very poor. We’ve gotten a lot better (and even with all its problems, I’d say current long-range forecasts are still better than Farmers’), but there are still high error rates in products like monthly and seasonal forecasts. As long as there’s that area of uncertainty, I think Farmers’ will find a niche. But more than that, it’s just fun to read, just like anything claiming a magical ability to predict the future. Just be glad we no longer live in a time where the Farmers’ Almanac is all we have.

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Heat Bursts

Temperature and dewpoint graph from the dramatic heat burst in Sioux Falls in 2008.  Credit: KELO-TV

Temperature and dewpoint graph from the dramatic heat burst in Sioux Falls in 2008.
Credit: KELO-TV

Heat bursts are rare and intriguing phenomena where air temperature spikes suddenly and dramatically. They are most common at night or during the early hours of the morning. These spikes are often accompanied by severe wind gusts and significant drops in dewpoint (which means the air is drying out significantly). Typically temperature jumps are roughly ten degrees in less than 30 minutes, but extreme cases have been reported. At 3 a.m. on July 11, 1909, the temperature spiked to 136 deg F over a small area south of Cherokee, Oklahoma. Crops were said to have instantly desiccated. Great Falls, Montana experienced a spike of +26 deg F in 15 minutes in the pre-dawn hours of September 9, 1994, topping out at 93 deg F and matching the record high for that day. The temperature was back down to 68 deg F just 20 minutes later. Two of the most well-documented heat bursts took place in Sioux Falls, South Dakota on August 3, 2008 and Wichita, Kansas on June 9, 2011. In Sioux Falls, the temperature rose from 74 deg F to 101 deg F in a matter of minutes in arguably the most dramatic heat burst ever reliably documented. Three years later in Wichita, the temperature went from 85 deg F to 102 deg F in 20 minutes between 12:22 a.m. and 12:42 a.m. This event was recorded by both the National Weather Service and numerous amateur weather stations in the Wichita area.

Temperature graph from the Wichita heat burst of 2011. This was a more prolonged event than the one that hit Sioux Falls three years earlier.

Temperature graph from the Wichita heat burst of 2011. This was a more prolonged event than the one that hit Sioux Falls three years earlier.

The most infamous heat burst, however, was the one that struck Kopperl, Texas on the night of June 15, 1960. Kopperl is a small town on the north side of Lake Whitney up the Brazos River about fifty miles southwest of Fort Worth. In the hours preceding the event, lightning flashes were seen in the far distance without any thunder being reported (commonly known as “heat lightning,” which is a misnomer…the lack of thunder has nothing to do with heat and everything to do with one simply being too far away to hear it). The temperature was about 70 deg F. Suddenly, just after midnight, the town was hit with a hot blast of wind in excess of hurricane force, reportedly knocking down trees and tearing the roof off a store. The wind was accompanied by a dramatic spike in temperature, surging well over 100 deg F. Thermometers capable of measuring up to 140 deg F reportedly broke as the alcohol inside rapidly expanded. The power in the town failed and people were awakened as their homes were suddenly sweltering and ran outside thinking the homes were on fire. People reported it was so hot, they had difficulty breathing. The next morning, cotton fields were found to be carbonized; burnt to the stalk. The event became known in local lore as “Satan’s Wind” or “Satan’s Storm.”

This story has been told many times and is often repeated in local newspaper articles on anniversary events and in articles posted about heat bursts. How much truth there is to the story is not clear. It was first published in a book about Texas weather by meteorologists Harold Taft and Ron Godbey from the NBC station in Dallas in 1975 and likely comes from local records and community tales. As with many oft-retold stories, over time, legend begins to replace facts. As the old saying goes, “everything gets better in the retelling.” It certainly seems that something dramatic happened there that night, however there is no record in the National Weather Service database of a severe wind event in Bosque County that night (although there was a tornado reported in far north Texas near the Oklahoma Panhandle that afternoon). What is definitively clear is that in the days that followed, a major heat wave struck that area of Texas.

A graphical depiction of how a heat burst occurs.  Source: MeteorologyNews

A graphical depiction of how a heat burst occurs.
Source: MeteorologyNews

Other wild stories of heat bursts have come from abroad. Near Lisbon, Portugal, the temperature supposedly rose from 100 deg F to an insane 158 deg F in two minutes on July 6, 1949. In Abadan, Iran, in June of 1967, a ridiculous shade temperature of 188 deg F was reported. Dozens of people supposedly fell dead and the streets and asphalt roads liquefied. These reports are likely both apocryphal. A report of 152 deg F from Turkey in 1977 also seems dubious. There is more support, however, for a report from Kimberley, South Africa of a 43 degree spike in just five minutes during a squall. The report comes from an observer at a local weather station but may be the result of faulty equipment. A significant heat burst likely did occur, however. At Gretna, Manitoba in Canada, there were two successive heat bursts in the early morning hours of July 21, 1960. The temperature spiked 16 degrees Fahrenheit in 15 minutes between 12:25 a.m. and 12:40 a.m. Then, just an hour and a half later, another, even stronger heat burst occurred, surging from the 70’s to 97 deg F also in just 15 minutes. Just last year, in January of 2014 in Melbourne, Australia, the temperature rose from 86 deg F to 102 deg F in roughly an hour. At the same time at the nearby Cerberus naval base, the temperature rose from 76 deg F to 90.5 deg F in just 30 minutes.

This animation shows a traditional "wet" downburst, which is far more visible and gives a good depiction of how powerful these events are.  Source: NWS

This animation shows a traditional “wet” downburst, which is far more visible and gives a good depiction of how powerful these events are.
Source: NWS

So what causes these events? Well, if you have an environment where there is cooler, moist air near the surface and a layer of hot, dry air up higher, what can happen is a thunderstorm moves into that environment and dies. In a thunderstorm, warm air rises in the updraft and cooler air (often accompanied by heavy rain, hail, and all that other fun stuff) comes down in the downdraft. When a thunderstorm dies, its updraft is choked off and it collapses as the downdraft dominates. This collapse can be quite violent, occasionally resulting in a phenomenon known as a “downburst.”

A downburst is a blast of wind caused by the downward surge of air as a thunderstorm collapses, frequently accompanied by heavy rain. When you have hot, dry air in the mid-levels above the surface, there’s no moisture to evaporate to cool the air and what happens is something called “compressional heating.” When air sinks down, it increases in density and causes compression of the molecules in the air, which generates heat. Normally this is offset by evaporating moisture, which has a cooling effect (this is what happens to your body when you sweat). However if there’s no moisture to evaporate, this cooling doesn’t occur. So, not only is the much warmer air aloft thrust down to the surface by the downdraft, the heat is dramatically increased because of the compression effect. This what causes a heat burst. This situation is most common in desert environments, where heating is stronger and that warm, dry layer in the mid-levels is seen more often.

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Great Balls of Fire – The Mystery of Ball Lightning

This spectacular image is believed to be the first time ball lightning was ever captured on film. It was taken in Japan in 1988.  Credit: Warren Faidley et. al., Weatherstock.com

This spectacular image is believed to be the first time ball lightning was ever captured on film. It was taken in Japan in 1988.
Credit: Warren Faidley et. al., Weatherstock.com

It’s among the most bizarre and mysterious natural phenomena that has ever been observed. “Ball lightning” is reported as a fiery ball of light that moves horizontally across the sky. Reports of ball lightning date back to the Middle Ages. In 1638, ball lightning supposedly struck the church of St. Pancras in Widecombe-on-the-Moor, England during a terrific thunderstorm. It crashed through a window, knocked the minister off his feet, singed clothing, and melted metal, but left the wood unharmed. This incident spawned numerous legends about how a local man made a deal with the devil where Satan could have his soul if he fell asleep in church. Supposedly he fell asleep that day. It’s easy to see why the people of that time would see something like that as the work of the devil. It was a ball of fire that smelled of sulfur and tore through the heart of the church.

Numerous ships reported seeing balls of fire in the sky. In 1726, the Catherine and Mary reported that a large fireball blew its mast into “ten thousand pieces.” In 1809, the HMS Warren Hastings reported three “balls of fire” struck the ship, killing two of their crew and setting their mast on fire. Tsar Nicholas II also reported seeing ball lightning as a child during a church service. These events were so rare and so spectacular (and terrifying) that a layer of mythology cloaked the real science, making it hard to separate fact from fiction.

Numerous spectacular tales of ball lightning entering buildings and other structures and causing all sorts of mayhem have been reported. In many of these cases, where the truth ends and the legend begins is murky. However ball lightning has been positively observed passing through the cabin of a plane.

Numerous spectacular tales of ball lightning entering buildings and other structures and causing all sorts of mayhem have been reported. In many of these cases, where the truth ends and the legend begins is murky. However ball lightning has been positively observed passing through the cabin of a plane.

With all this in mind and given the dearth of hard evidence, up until the 1960’s, scientists believed that ball lightning was just an urban legend, despite numerous credible reports. Then, in 1963, a group of scientists flying from New York to Washington, DC saw a bright ball of light move down the aisle and exit out the back of the plane. This incident sparked renewed scientific interest in the phenomena and a number of studies followed. A report in 1972 identified numerous distinct characteristics about it. One thing that is clear is that ball lightning is not very consistent. It almost always occurs during or immediately following a cloud-to-ground lightning strike. Their size varies widely but they’re typically about the size of a grapefruit. It’s about as bright as your standard floor lamp and virtually every color in the rainbow has been reported, with yellow, red, and orange being the most common. They last anywhere from a second to over a minute.

Given that it took decades for scientists to even prove that ball lightning exists, it’s not surprising that its cause remains a mystery. A number of theories have been proposed. The most popular theory is ball lightning is in fact vaporized silicon. Earth’s soil is very rich in silicon dioxide, or silica, and the theory goes that when lightning strikes the ground, that silica is vaporized and split from the oxygen, turning it into pure silicon vapor. This vapor condenses into dust as it cools and is pulled together by the electric charge imparted by the lightning strike. The resulting “ball” of silicon-rich dust recombines with the oxygen in the air, a process (known as oxidization) that generates heat, causing the ball to glow. When the silicon burns out, the ball dies.

A spectrograph showing the mineral composition of ball lightning based on data from the Chinese team.  Credit: Olli Niemintalo

A spectrograph showing the mineral composition of ball lightning based on data from the Chinese team.
Credit: Olli Niemintalo

Science has only recently started to get a handle on the phenomenon. Most recent experiments have focused on the vaporized silicon theory. In 2007, researchers from the Federal University of Pernambuco in Brazil were able to replicate this process. They shocked samples of silicon with electricity and were able to produce glowing balls about the size of a golf ball. Eli Jerby and Vladimir Dikhtyar of Tel Aviv University created ball lightning by accident while using a powerful microwave beam to drill into a chunk of silicon. Then, in January, 2014, scientists from Northwest Normal University in Lanzhou, China dropped a bombshell. In July, 2012, a scientific team from Northwest Normal was conducting a study of traditional lighting on the Tibetan Plateau when they observed a glowing ball streaking across the sky just 3,000 feet away from them, lasting approximately two seconds. Their proximity to the event allowed them to capture it with their instruments, including several high tech cameras and spectrographs.

A rare image of ball lightning taken in the Netherlands.  Credit: Joe Thomissen

This image believed to be of ball lightning was taken in the Netherlands in 2011.
Credit: Joe Thomissen

Using this data, they were able to determine the composition of the ball’s emissions, which they published in a detailed report in 2014. With traditional lightning, usually only ionized nitrogen is observed. With ball lightning, however, scientists found atomized nitrogen, oxygen, calcium, iron, and…you guessed it…silicon. Calcium, iron, and silicon are all minerals that are common in soil. This is a big win for the theory that ball lightning is a chemical reaction caused by minerals in the ground that are vaporized and electrified by a lightning strike.

There are still many things we don’t understand about this amazing and bizarre phenomenon. How does it go through walls and manifest in enclosed spaces? If it’s caused by lighting hitting the soil, why is it so rare? Are there different types? Many, many questions still remain. But we are getting closer. After hundreds of years of mysterious tales, ball lightning is finally stepping out of the realm of legend and into the realm of science. And I think that’s pretty exciting.

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Nature’s Light Show – The Science of Lightning

A spectacular lightning display over Quebec.  Source: JP Marquis

A spectacular lightning display over Quebec.
Source: JP Marquis

Among nature’s most spectacular phenomena is lightning. Lighting up skies throughout the world millions of times per day, coming in bright flashes and brilliant bolts. What causes this amazing spectacle? It’s all about electrical energy. There remains some debate about exactly what happens, but the basic theory is that essentially an electrical circuit develops between the thunderstorm and the ground, as well as within the cloud itself. Inside a thunderstorm, strong updrafts heave water droplets high into the air, where they freeze into ice pellets. Downdrafts then hurl these ice pellets back down toward the surface. On the way, they run into other water droplets that then freeze on contact as well as other ice pellets that freeze together. This is how hail forms. These collisions cause electrons (which have a negative charge) to break off of drops going up in the updraft and collect on the ones coming down in the downdraft. This gives you a positive charge at the top of the cloud and a negative charge at the bottom of the cloud.

In this graphic, you can see how the most common forms of lightning develop and how the charges are distributed.  Source: University of Alaska-Fairbanks

In this graphic, you can see how the most common forms of lightning develop and how the charges are distributed.
Source: University of Alaska-Fairbanks

Remember from high school science class: opposites attract. When you have a difference in charges, it can form an electric field. This is what happens in storm clouds. An electric field develops between the top and the bottom of the cloud. Fortunately for us, the atmosphere is a pretty good insulator, which prevents the sky from lighting up like a Christmas tree with every shower (during the Carboniferous Period roughly 300 million years ago, the atmosphere was much more oxygen rich than it is today, which made the atmosphere much more sensitive to electric charge, producing frequent spectacular thunderstorms unlike any we see today). Because of the insulating effects of the modern atmosphere, an incredible amount of charge has to build up in order to produce lightning. As the updraft strengthens, the charge increases. Eventually it builds up enough to overcome the insulation and you get lightning. This is of the intracloud variety where lighting occurs within the could itself. Lighting can also run between two different thunderstorm clouds, between the positively charged top of the cloud and negatively charged bottom of another. This is cloud-to-cloud lightning; bolts that snake across the sky.

An animation showing how traditional cloud-to-ground lightning forms.  Source: Science Joy Wagon

An animation showing how traditional cloud-to-ground lightning forms.
Source: Science Joy Wagon

How does that lightning get to the ground? As the thunderstorm moves, a positive charge builds up on the ground underneath it. Meanwhile, a string of negative charge begins to descend from the cloud. This is called a “stepped leader.” As the charges strengthen, the positive charge on the ground envelopes ground features such as trees, telephone poles, even houses. The charge climbs up as the leader drops down until they meet in a brilliant bolt of lightning.

The reason prominent objects, like trees and tall buildings, are at higher risk is because they effectively decrease the distance between the cloud and the ground, thus requiring less energy to produce a lightning strike. Lightning, as with many things in nature, tends to take the path of least resistance. That doesn’t mean lightning will always strike the tallest object. Exactly what causes lightning to strike a specific place at any given time is something of a mystery, but it’s always where the charge is the strongest, be it a tall tree or a flat field. There are some objects, like metal poles, which are better conductors of electricity and may be more likely to get struck even though there might be, for example, a much taller tree nearby. After an initial lightning strike, if there’s enough charge left over, additional strikes can follow the same path. If you’ve ever seen a lightning bolt that flashed more than once, that’s what’s happening. Sometimes little pieces of charge can extend out, away from the main channel, which is what causes the little forks of lightning we occasionally see.

This spectacular image taken by the late meteorologist Al Moller in 1976 is an excellent example of a positive lightning strike.

This spectacular image taken by the late meteorologist Al Moller in 1976 is an excellent example of a positive lightning strike.

There are several different types of lightning. Described above is the most common form, known as negative lightning. However, there is another type called “positive lightning.” Unlike negative lightning, which tends to come out of the base of the thunderstorm, positive lightning comes from the top of the cloud and is positively charged. What happens is that a negative charge builds up on the ground in the wake of a thunderstorm, and on rare occasions the positive charge at the top of the cloud and the negative charge on the ground become powerful enough for their leaders to meet in a bright, long, incredible bolt. These events make up less than 5% of all lightning strikes. The reason is that it takes an incredible amount of energy for them to overcome the much greater distance through the atmosphere. As a result, however, these bolts (sometimes referred to as “Superbolts”) are extremely powerful and dangerous. Superbolts are up to ten times more powerful than average lightning, producing up to one billion volts. Yes, BILLION, with a “B.”

Diagram showing a typical example of a positive lighting strike.

Adding to the danger is that the nature of the charge means that most positive strikes occur well away from the thunderstorm, sometimes as much as ten miles away. They have been reported in areas where no thunder was audible…a proverbial “bolt from the blue.” Positive lighting is also many times brighter, hotter, and longer-lasting than negative lightning, and release a large amount of VLF (Very Low Frequency) and ELF (Extremely Low Frequency) radio waves. They are believed to be responsible for a large percentage of lightning-caused forest fires. They may also be the source of a strange phenomenon called “sprites,” which are little electric discharges observed high in the atmosphere above the tops of thunderstorms. They are often seen by satellites and orbiting astronauts. Sometimes lightning can change polarity (turning from positive to negative and vice versa). This is called “bipolar lightning.”

Another incredible shot of a positive lightning strike.  Source: Kara Swanson/National Geographic

Another incredible shot of a positive lightning strike.
Source: Kara Swanson/National Geographic

There are some incredible reports about the power of “superbolts.” In 1838, the top-gallant mast of the HMS Rodney was struck and “instantly converted to shavings. The sea looked as if the carpenters had swept their shavings overboard.” A church belfry in England was struck with a bolt so powerful that a stone weighing 350 pounds was thrown 60 yards over the roof and another stone of unknown size was tossed a quarter of a mile. No date was given with this event. In 1959, farmers in Leland, Illinois reported a blinding flash and deafening thunder that shook houses violently enough to break windows and throw loose objects to the floor. Many of them thought they’d been directly hit, but in fact it was an incredibly powerful bolt that struck three quarters of a mile away in a cornfield, leaving a crater roughly ten feet wide and a foot deep. (Extreme Weather, Christopher Burt, 2003, p.149)

What about thunder? How is that created? Well, lightning is extremely hot, as much as 30,000 degrees Celsius (54,000 degrees Fahrenheit)…five times as hot as the surface of the sun! The air we breathe is a gas, and when you heat gas up, it expands. A lightning flash superheats the air around it instantaneously, causing the air to explosively expand beyond the speed of sound and create essentially a sonic boom. Light travels WAY faster than the sound, which is why you see lightning long before you hear it. When the lightning strike is close by, it sounds like a loud boom or crack. This means you’re close enough to hear the single initial shockwave. When you’re farther away, the sound waves blend together and create more of a prolonged rumble. Temperature also makes a difference. If it’s warmer outside, the sound waves travel faster and thus you will hear thunder sooner. When it’s cold out, the sound waves are slower and take longer to reach your ears. The above video shows a lightning strike slowed down frame by frame. You can see the initial strike with branching, followed by a return stroke (the secondary flash).

Credit: William Curstinger

Credit: William Curstinger

Roughly a hundred Americans are killed by lightning every year. How do you stay safe? Well first, I know it sounds kind of obvious, but don’t be outside in a thunderstorm if you don’t absolutely have to be. All that does is add risk. If thunder roars, go indoors! If you hear thunder, you need to find your way to a safe place. If you are outside and there’s no public building or other shelter nearby, getting in your car is the best option, but any sort of open vehicle like a convertible or golf cart isn’t safe. But most importantly, always keep an eye on weather forecasts whenever you’re planning outdoor activities and always have an idea of what you will do if there’s a lightning threat. Lighting is spectacular display but it is also very dangerous and must always be treated with respect.

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What is the Sea Breeze?

The black arrows point to developing sea breeze thunderstorms. On two of them, you can clearly see a line of small clouds adjacent to the thunderstorms that mark the location of the sea breeze front.  Source: University of Wisconsin

The black arrows point to developing sea breeze thunderstorms. On two of them, you can clearly see a line of small clouds adjacent to the thunderstorms that mark the location of the sea breeze front.
Source: University of Wisconsin

Have you ever been at the beach and noticed thunderstorms build in off the water during the afternoon? That is frequently the result of the sea breeze. You may have heard forecasters on TV use the term before. What is it? It’s all about temperature differences. The ocean absorbs heat from the sun much more effectively than land. The land surface gets hot during the day and cools significantly at night, resulting in large diurnal (day-night) temperature differences. The ocean, meanwhile, has a much smaller day-night temperature fluctuation. During the day, the ocean is significantly cooler than the land. During the summer, this difference is magnified and can cause a circulation to develop.

Schematic showing the sea breeze circulation and the development of the sea breeze front.  Source: NOAA

Schematic showing the sea breeze circulation and the development of the sea breeze front.
Source: NOAA

Physics tells us that warm air rises and cold air sinks, right? Well, what happens during a hot summer day is that warm air rises off the hot land, leading to relatively low pressure at the surface. Higher up in the atmosphere, the air cools and settles, leading to higher pressure aloft. Over the water, the air remains cooler and sinks down to the surface and spreads out (diverges), creating relative high pressure at the surface and low pressure aloft. A basic rule of meteorology is that air wants to move toward areas of lower pressure, so in this situation, the differential pressure causes a circulation. The cooler, denser air mass over the water moves toward the lower pressure on land, clashes with that warmer air mass, and you get a small-scale front. As with a large-scale front, warm air is lifted over it and can generate thunderstorms in the right conditions, with the ocean providing a constant source of moisture to fuel the storms. As the front moves inland farther away from the coast, the temperature difference (or “gradient”) weakens and the front dies out, taking the thunderstorms with it.

Schematic showing the land breeze circulation and the development of the land breeze front.  Source: NOAA

Schematic showing the land breeze circulation and the development of the land breeze front.
Source: NOAA

At night, this process is reversed. The land loses heat much more quickly than the ocean, which results in the land being cooler than the oceans. This allows high pressure to develop over land and low pressure over the water, flipping the circulation and forming what is known as a “land breeze”. A land breeze is just like a sea breeze, except the front pushes off the land out over the water. Land breezes are typically weaker and don’t produce thunderstorms. This is because land breezes form in a more stable environment. The cooling land surface doesn’t allow for the lifting necessary for thunderstorm development and the temperature gradient in a land breeze situation is not as strong as with the sea breeze. There is also very little heating present and terrain features of the land surface (trees, buildings, etc.) block air flow from the land to the water. They can, however, result in cloud development. Unlike sea breezes, which occur predominantly in summer, land breezes are more common in the fall and winter, when nighttime temperature differences are the greatest.

A radar image of a lake breeze event over the Chicago metro area. The lake breeze front is clearly visible as the blue line along with its attendant thunderstorms. This event was aided by a large-scale cold front and outflow from previous thunderstorms.  Source: NWS Chicago

A radar image of a lake breeze event over the Chicago metro area. The lake breeze front is clearly visible as the blue line along with its attendant thunderstorms. This event was aided by a large-scale cold front and outflow from previous thunderstorms.
Source: NWS Chicago

The strength of sea breezes is significantly affected by the strength and direction of the prevailing wind. Prevailing winds off the water during a summer afternoon can strengthen the sea breeze and help it penetrate farther inland. Light winds off the land, or opposite the direction the front is moving, can pin the sea breeze near the coast but also allow much more significant and widespread thunderstorm development. Stronger opposing winds, however, can keep the sea breeze over the water, thus preventing thunderstorms from developing at all. On smaller peninsulas, opposing sea breezes can actually collide and lead to very intense, though short-lived, thunderstorms. On larger peninsulas, the opposing sea breezes typically weaken before they reach each other.

This phenomena isn’t restricted to oceans. Any large body of water can experience sea and land breezes. On the Great Lakes, they are known as “lake breezes” and can have exactly the same effects as their oceanic counterparts. Lake breeze thunderstorms are quite common during the summer along the Great Lakes and can be very persistent, due in part to the geography and wind patterns of the Great Lakes region.

So, the next time you go to the beach, keep an eye out for this neat little phenomena. But remember to be safe about it. These storms don’t usually last long but they can be pretty nasty. “When thunder roars, go indoors.” You can always come back later.

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Anatomy of a Heat Wave

heat

Man, it’s hot out there! Summer is in full swing and many parts of the US are experiencing their first significant heat wave of the season. That begs the question: what causes a heat wave? Well, the short answer to that is generally a large, tropical high pressure system. A high pressure means air is converging high in the atmosphere and sinking down to the surface, where it spreads out, or diverges. This sinking air has a drying effect, clearing out clouds and leaving us to roast in the summer sun. High pressure systems can also bring in much warmer air from the south, further intensifying the heating. It also has a bad habit of killing off any cooling breezes. In the southeast, however, the drying effect of the sinking air is limited by the tropical influence of the Gulf of Mexico and Atlantic Ocean, with moist air coming off the water. This limits how high temperatures will climb and allows some cloud formation, but it also greatly increases dewpoints and relative humidity. This causes much higher heat indices, or apparent temperatures. In the desert southwest, this tropical moisture is absent, which keeps the relative humidity down but allows temperatures to soar well into the hundreds.

Today's high temperatures, showing the heat spread across the southeast and southwest, as well as the plains of Kansas.  Source: NOAA

Today’s high temperatures, showing the heat spread across the southeast and southwest, as well as the plains of Kansas.
Source: NOAA

The traditional setup for a heat wave is much like the reverse of a cold wave. In the winter, big Arctic high pressures sweep down from Canada, bringing frigid Arctic air with it. The lack of cloud cover allows the Earth’s surface to lose a lot of heat at night through radiative effects and causes temperatures to plummet. In a heat wave, strong tropical high pressures build in from the south (in the southeast, they can also come from the west or southwest, or the Atlantic to the east), bringing in warmer air from the deserts of northern Mexico, or the tropical Atlantic or Gulf of Mexico. As I mentioned earlier, the clearing of clouds during the peak of the day allows for vastly increased solar radiation. In the Deep South, temperatures closest to the coast are moderated by the presence of the ocean. However, once you move farther inland, there is a stronger continental influence with just enough tropical air to strongly impact heat indices. What you end up with over the interior Deep South is hot and sticky weather with the ever-present chance of thunderstorms.

So what’s happening now? The heat wave in the southeast is cresting today and into tomorrow and is expected to break by the weekend as the high pressure begins to break down. Heat index values as high as 110 can be expected over portions of the South. This intense heating plus the presence of tropical moisture brings with it the possibility of thunderstorms, particularly in the peak of the afternoon. These thunderstorms can develop quickly and are very difficult to predict.

The west is about to really heat up as a high pressure moves north and sets up an intense heat wave. Source: The Weather Channel

The west is about to really heat up as a high pressure moves north and sets up an intense heat wave.
Source: The Weather Channel

While the South may be cooling off this weekend, the west will be getting even hotter. This one may set records. A high pressure is moving north-northwest from Mexico and bringing intense heat with it. The high temperature in Boise, Idaho is expected to be 107 deg F both Sunday and Monday. Parts of eastern Washington, Oregon, and Idaho could approach 110 deg F. Missoula’s June record of 100 deg F, which has stood for 97 years (it was matched in 1937), is expect to fall, with 102 deg F forecast for Sunday. Nearby Kalispell has never seen triple digit temperatures in June. They’re expected to reach 101 on Sunday. Spokane, Washington’s all time record is 108 deg F. It’s expected to reach 105 on Sunday. Portland, Oregon’s June record is 102 deg F, set in 2006. They’re forecast to reach 101 on Saturday. That record could be in jeopardy. Reno, Nevada’s June record is 104 deg F and they could hit 102 both Friday and Saturday. Salt Lake City’s June record is 105 deg F and they are expected to see 102 on Monday and Tuesday, the final two days of June. Many areas could see one hundred degree temperatures for several consecutive days, threatening further records. Triple digit heat is expected to reach as far north as southern Canada.

So how do you beat the heat? Stay inside as much as possible, but if you must be outside, drink lots of water and take plenty of breaks. Limit time outside as much as possible. Also remember to wear plenty of sunscreen. And watch out for thunderstorms. Remember, when thunder roars, go indoors!

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