by Mark SumnerThe first days of April 1974 were perfect for thunderstorms. On April 1, a strong low-pressure system settled across the Upper Midwest. On one side of this low pressure dry, very cold air began to descend from the Canadian interior. At the same time, warm moist air surged up from the Gulf of Mexico. As a front built up across the country, the differences between one side and the other were extreme. For the next two nights, thunderstorms appeared around sunset and people across the Midwest were kept awake by rocketing winds and lightning storms so constant that the pyrotechnic display turned into one continuous pulse of flashing light accompanied by pounding drums.
On April 3, the atmosphere exploded. In a line stretching from Michigan to Alabama, potent "supercell" thunderstorms formed as a strong upper level jet stream finally sent the cold air crashing through the warm. In storm after storm, whirling mesocyclones developed high in the atmosphere and in storm after storm cold air along the front dragged downward on these vortexes, hurling them to the earth. Just after noon, a tornado was spotted on the ground in central Illinois. More tornadoes were born, sped through towns and farmlands of Illinois and Indiana, and faded to twisting ropes. Quickly the activity spread east and south, and as it did, the tornadoes grew more intense.
Tornadic storms are rated on a scale developed by Dr. Ted Fujita of the University of Chicago. The scale is intended to judge the intensity of the storm based on size and wind speed, but the measurement is almost never made directly. It's made by looking at the damage. There was plenty of damage on April 3, 1974.
Most tornadoes fall in classes F0 and F1. These storms are still dangerous, with the power to topple light buildings, bring down tree limbs, and push cars into ditches. About a fifth of all tornadoes are F2 storms, able to uproot large trees, smash windows, and send objects whirling through the air. Moving upward along Dr. Fujita's scale, the frequency of storms drops quickly once you're past F2. Only about one tornado in twenty reaches F3 – which is a good thing, as these storms are able to level homes, lift cars from the ground, and twist even steel-framed skyscrapers. One out of a hundred reaches F4, where even the best-built buildings are liable to be leveled, cars aren't just lifted but thrown through the air, and where bricks, boards, and trees become screaming missiles. About one tornado in a thousand reaches F5. F5 storms can have wind speeds above 300 miles per hour. They can be a mile, even two miles, in width. In an F5 storm, even houses become missiles. F5 storms are erasers.
In a two hour period on the afternoon of April 3, 1974, at least six F5 storms were spawned across the Midwest. Just before 5PM, one of these storms plowed through the city of Xenia, Ohio. It struck a high school where students practicing for a play scattered in time to avoid a school bus that was dropped into the middle of the stage. The students survived. Residents of subdivisions along the city's west side were not as lucky. 34 people died as literally half the town was leveled in the space of minutes. When the Xenia storm had faded, there were five more F5 tornadoes on the way. By the afternoon of April 4, 163 confirmed tornadoes had spread out over 13 states and traced out a combined path of destruction over 2,500 miles long. More than 300 people were dead.
The "Super Outbreak" of 1974 is the worst day of tornadoes and thunderstorms on record in the United States, and the United States is the world capitol of tornadoes. This is about as bad as it gets when it comes to weather over land.
Having watched in horror as Hurricane Katrina blasted through the City of New Orleans, you may think you've seen the worst that storms originating over water can do. In terms of pure dollars of damage, Katrina did $81 billion in direct damage and the total bill topped $100 billion. Much of this damage remains unrepaired. (In other words, it cost about as much as one year of the war in Iraq, and while it may be patriotic and freedom-loving to spend that money causing death and destruction elsewhere, it's traitorous socialism to spend an equal amount creating jobs, helping neighbors, and building homes in America...)
The power of hurricanes (in the North Atlantic and NE Pacific) is measured on a scale named for engineer Herbert Safir and meteorologist Bob Simpson. Like the Fujita scale for tornadoes (and the Richter Scale for earthquakes) Safir-Simpson was originally based around the amount of damage that could be expected from a storm, though these days it's completely defined by wind speed.
On any scale, Katrina was a particularly erratic storm. One day before it struck Florida, Katrina was still an unnamed tropical depression with winds below 40 mph. It reached tropical storm status on that last day, and crossed the line into hurricane force winds only two hours before striking southern Florida on August 25, 2005. Though the National Hurricane Center had correctly predicted the storm's growth and shelters were opened, many people were taken off guard by the rapid change, which helps explain why 14 people died in Florida as Katrina passed across the peninsula and entered the Gulf. The Gulf waters were extremely warm that year, and the energy of those waters quickly returned the storm to hurricane status. At one point in its development, Katrina carried winds of 175 mph – a record that was broken later that same year by Hurricane Rita. At that speed, Katrina was a Category 5 storm. Fortunately, by the time it reached landfall in Louisiana on the storm had weakened somewhat to a very strong category 3. It reached the coast with winds of 125 mph, pushing a storm surge of 12-16 feet. That surge would go on to break the levees of New Orleans in over 50 places. In total, over 1800 people would die. Most of them drowned either as a direct result of the storm surge, in areas affected by the broken levees, or from flooding associated with the storm's heavy rains. The nation looked on in horror.
What may be surprising is that Katrina is not the deadliest hurricane to rise out of the Atlantic. In fact, it's not even in the top ten. Even if we restrict ourselves to hurricanes that did their damage in the United States, there are storms that caused more damage and took more lives.
In 1928, a storm formed in the Mid-Atlantic, several hundred miles east of the small archipelago of Guadeloupe, and began to move almost directly westward. By the time it reached the islands of the Eastern Caribbean, the storm was carrying winds in excess of 120 mph and pushing a wall of water a dozen feet high that surged over homes and drove ships inland. That would have been bad enough, but as it pressed on it ran into warm currents that gave it more strength and winds that slowed its forward motion. The hurricane slowed almost to a stop. And grew. It reached Puerto Rico on September 13 and by tradition became "Hurricane San Felipe" – named for the saint whose feast day matched the landfall. Saint or no, the winds of the storm were in excess of 160 mph – Category 5. Creeping along, San Felipe battered the island with hurricane force winds for 18 straight hours, and slashed the island with a twelve foot storm surge and 25 inches of wind driven rain. Because the storm had approached so slowly, there had been time to give many warnings and to evacuate areas near the coast. Fatalities were "only" 312. Then the storm turned toward Florida. Again, the warning time meant that the coasts could be evacuated and causalities there were light. But there was another coast that was not as prepared – the shoreline of Lake Okeechobee. Inland residents had thought themselves safe from the storm, but the hurricane arrived almost perfectly aimed at the Lake and its many vacation homes and fishing lodges. The storm surge carried across the low ground between ocean and lake, then across dikes, dams, and canals. Twenty feet of water carried homes into the lake and into surrounding forests and fields where they were smashed like kindling. The death toll ran upwards of 3,000 and for weeks afterwards floodwaters carried bodies into the Everglades.
And that still wasn't the worst. There was no organized system for tracking hurricanes in 1900, but at the end of August ships traveling new the Windward Islands reported difficult weather. By September 4, officials in Galveston, TX received notice from the weather bureau that a tropical storm was affecting Cuba. There was no way to know which way it would go from there, though the best guess was that it would turn up along the coast of Florida. It didn't. At dawn on September 8, 1900 skies in Galveston were clear, but those looking out at the water – which on that Saturday morning included many visitors to the area -- noticed particularly large swells rolling into the beach. A few hours later, clouds began to scud across the sky. Isaac Cline, the head meteorologist for the US Weather Bureau office in Galveston, had written an article some years earlier saying that the idea of a hurricane striking the city was "ridiculous." The article had been a big factor in halting plans to build a sea wall to protect the city. But on that morning, Cline had his doubts. Increasingly concerned by what he was seeing in the skies over the Gulf and by the heavy, rising chop of the waves, Cline bypassed official channels. At noon, he issued a hurricane warning without waiting for permission from Washington. At 5pm hurricane force winds reached the city. Cline's office recorded speeds of 100mph, at which point the instruments were destroyed. It's likely that the storm which reached Galveston that Saturday afternoon was a Category 3 storm, with wind speeds matching those of Hurricane Katrina. As darkness fell, the eye of the storm passed over the city and wind direction changed. With that change in winds came a 15' storm surge. The highest point in Galveston was 9'. In the next hour, somewhere around 8,000 people (and possibly as many as 12,000) drowned as the island temporarily vanished beneath the wild sea.
These are all interesting, if terrifying events, but what good does it do us to review and morn these catastrophes? Maybe it would help to review another storm.
In 1915, another hurricane struck Galveston dead on. As with the 1900 storm, this one was a category 3. In fact, the winds of this storm were higher -- 135 mph -- and it also carried with it a storm surge of 12-15 ft.
In May of 2004, another great outbreak of tornadoes occurred. 389 twisters hit over an 11-day period as a series of fronts clashed over the Plains and Midwest. Over the Memorial Day weekend, violent tornadoes cut across Missouri, Illinois, Nebraska, and Iowa, including one tornado that was 2.5 miles wide, the largest known.
Why bring these up?
Because of what happened between 1900 and 1915, and what happened between 1974 and 2004. After the almost incomprehensible disaster of 1900, the City of Galveston finally built that sea wall. They also dredged sand from the harbor and raised the elevation of the island by several feet. In addition, the weather service was much more vigilant after 1900. More stations were set up to track storms, and warnings were given earlier and across a wider area. All of these help to shape the reason why the first Galveston hurricane is remembered as a monster and this second storm is all but forgotten. When the second storm struck, the death toll in Galveston wasn't 12,000 or 8000. It was 11.
In the 2004 tornado outbreak, a total of 7 people died. There were twice as many tornadoes as the 1974 event (though fewer F5s) and the property damage was several times greater. Why were the human causalities so much less than in 1974? There were much less knowledge about how tornadoes form and no Doppler radar to spot their incipient appearance. The tornadoes that hit town after town in 1974 might as well have appeared by magic. In most towns (including Xenia) there was no early warning, no system of sirens, no plan for how to respond. On the other hand, when an F5 tornado obliterated the town of Greensburg, KS in 2007 the tornado was literally wider than the town. It didn't take out half the buildings, it took them all. 12 people died, but the number could have been in the hundreds if it hadn't been for a warning system that gave most people in the town a critical 20 minutes to find shelter.
Not every disaster is avoidable. We may never be able to stop a tornado in its tracks or alter the course of a hurricane. But the expenditures we make to research causes, provide warnings, and plan responses are far from wasted. Yes, there are some classes of disaster that may be so enormous, or so unlikely, that addressing them is pointless. No one should put any funds behind a "Stop the Sun from Expanding" committee. But there are a great swath of events in the middle ground where planning and consideration may greatly reduce, if not eliminate, the consequences. Next week I hope to look at some of the possible challenges we may face (from nature this time, not at our own hands) to see which of them might be worth an investment of time and materials.
Oh, and one last quick note. The population of Galveston when the great hurricane swept through in 1900 was around 42,000 -- less than 1/10th that of the City of New Orleans itself (not to mention surrounding communities) in 2005. Over 1800 people died in Katrina (including some who perished in the post-storm chaos), but tragic as that number is it's much smaller than what might have happened if a well-informed National Hurricane Center had not contacted an alert mayor who responded quickly to get most of the city's populace on the road. If New Orleans had suffered losses proportional to those in Galveston, the count could have been in six figures (and if you think that can't happen, look at up the results when Hurricane Mitch dropped 75" of rain on Honduras, Guatemala, and Nicaragua in 1998, or the toll from the 1970 Bhola cyclone).
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