Patty Ingalls, NSSL NOAA via Flickr // CC BY-ND 2.0
Patty Ingalls, NSSL NOAA via Flickr // CC BY-ND 2.0

Why Does It Seem Like Tornadoes Target Mobile Homes?

Patty Ingalls, NSSL NOAA via Flickr // CC BY-ND 2.0
Patty Ingalls, NSSL NOAA via Flickr // CC BY-ND 2.0

The idea that tornadoes are magnetically attracted to mobile home parks is almost a morbid joke in the United States—a way to cope with the predictable horror of seeing these vulnerable communities destroyed year after year, killing and injuring dozens of people. Mobile homes, commonly known as trailers, are so frequently destroyed in bad storms that it almost seems like these structures are targeted for destruction by tornadoes. The factoid is somewhat true, but for the wrong reasons.

A map showing the tracks of every recorded tornado in the United States between 1950 and 2015. Map: Dennis Mersereau

The United States averages about 1000 tornadoes every year. Most of those tornadoes touch down in the central and southern parts of the country, but they can and do happen in all 50 states. A huge majority of tornadoes—80 percent, in fact—don’t cause too much damage and wind up on the lower end of the Enhanced Fujita Scale, which is used to estimate a tornado’s winds based on the damage it produces.

Most structures can stand up against the winds of a small tornado. Not without damage, of course, but if you’re in a well-built home or office building, you have good odds of coming out of an EF-1 tornado with four walls and most of a roof dangling above you. Mobile homes are much different.

A map showing the percentage of mobile homes in each county and parish in the United States. Map: Dennis Mersereau

A significant percentage of homes in rural parts of the United States are mobile homes. The number of residences that are mobile homes is greater than 10 percent in many parts of the South, the West, and around the Appalachian Mountains. The number of mobile homes in the South is particularly concerning when you overlay historical tornado tracks on the above map.

All recorded tornado tracks between 1950 and 2015 overlain on top of the percentage of mobile homes by county. Map: Dennis Mersereau

Here we get to the crux of the issue. Tornadoes don’t go out of their way to hit mobile homes—you’re just more likely to live in one of these homes if you live in places where tornadoes are common. Compounding the issue is the fact that mobile homes simply aren’t built to withstand the winds of a bad thunderstorm, let alone a tornado. A huge part of tornado safety relies on the sturdiness of the building that takes a direct hit. Many mobile homes are built with cheaper construction materials that aren’t rated to withstand a fraction of the winds of a sturdier structure.

Tucked away in the guidelines that the National Weather Service uses to estimate the strength of tornadoes are their estimates for how strong a tornado’s winds have to be to destroy a standard, single-wide mobile home. According to their scale, it only takes winds of about 87 mph to shift a mobile home off its blocks. Winds of 89 mph are sufficient to peel the roof off the home. The entire mobile home begins to flip over and roll downwind once a tornado’s wind speed climbs up around 98 mph. The whole building is destroyed once winds exceed 100 mph.

Those destructive 100 mph winds would make a tornado rated an EF-1, which is on average the most common rating for tornadoes in the country. But 20 percent of all tornadoes that touch down are stronger than that, and many of them occur in regions where lots of people live in mobile homes. Compare that to the damage a single-family home would sustain in the same tornado: broken windows, a busted garage door, a broken chimney, and some roof damage. It’s a far cry from losing everything (and possibly everyone) you know and love. That’s the terrifying reality that many people face each spring and summer, and it’s why mobile homes are so frequently damaged in destructive storms. 

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Britain Is in the Midst of a Rare ‘Wind Drought’
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Generating renewable energy in Britain is a little less than a breeze these days: A “wind drought” is halting the country’s wind turbines.

This month’s wind energy output is down 40 percent from the same time last year, New Scientist reports. On average, about 15 percent of Britain’s electricity comes from wind power. Data starting from July 1 of this year put the monthly average closer to 6.9 percent. Last month, turbines were producing less than 2 percent of Britain’s electricity—the lowest output in two years.

That’s with even more wind turbines being installed over the course of the past year, New Scientist says. The data aren’t entirely surprising, though. The jet stream tends to make the UK’s weather drier and calmer during the summer and wetter and stormier during the winter. But the high pressure the jet stream has brought with it this year has been unusually prolonged, scientists say.

“It’s like a lid, it keeps everything still,” UK Met Office spokesperson Grahame Madge told New Scientist. “From the forecast looking out over the next couple of weeks, there doesn’t seem to be any significant change on the way.”

The wind drought shouldn’t cause too many problems in the short term. Electricity demand is low during the summer (very few British homes have air conditioning), and the country’s been able to compensate for the lack of wind by burning more natural gas. If the wind drought continues to persist, though, UK residents may begin to see an increase in utility fees. Natural gas prices have already risen with the increased demand.

“As we continue to transition to a low-carbon energy system, managing the intermittency of renewable power an important role in balancing supply and demand,” a National Grid spokesperson told New Scientist. “However, we have planned for these changes and [are] ready to play our part.”

The wind drought comes about eight years after British politicians vowed to reduce the UK's dependence on fossil fuels. Last year was the first year that electricity generated from low-carbon energy sources like solar power, wind power, and nuclear power outpaced high-carbon energy sources like coal and natural gas. This summer’s wind drought may make it difficult to improve on last year’s numbers.

[h/t New Scientist]

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Drought Reveals Ancient Sites in Scotland That Can Only Be Spotted From the Air
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iStock

Typically rainy Scotland is in the middle of an unusually dry summer—and local archaeologists are taking advantage of it. As the BBC reports, the drought has revealed ancient sites, including Roman camps and Iron Age graves, that have been hidden by farm soil for years.

Historic Environment Scotland has been conducting aerial surveys of the country's landscape since the 1930s, but it's in seasons like this, when the crops recede during dry weather, that the buried remains of ancient structures are easiest to spot. Conditions this summer have been the best since 1976 for documenting archaeological sites from the sky.

Aerial view of field.
Historic Environment Scotland

The crescent-shaped crop mark in the photo above indicates a souterrain, or underground passageway, that was built in the Scottish Borders during the Iron Age. The surveyors also found remains of a Roman temporary camp, marked by straight lines in the landscape, built in modern-day Lyne—an area south of Edinburgh already known to have housed a complex of Roman camps and forts.

Aerial view of field.
Historic Environment Scotland

In the image below you'll see four small ditches—three circles and one square—that were likely used as burial sites during the Iron Age. When crops are planted over an ancient ditch, they have more water and nutrients to feed on, which helps them grow taller and greener. Such crops are especially visible during a drought when the surrounding vegetation is sparse and brown.

Aerial view of field.
Historic Environment Scotland

Historic Environment Scotland has a team of aerial surveyors trained to spot the clues: To date, they've discovered more than 9000 archaeological sites from the air. HSE plans to continue scoping out new areas of interest as long as the dry spell lasts.

It's not just in Scotland that long-hidden settlements are coming to light: similar aerial surveys in Wales are finding them too.

[h/t BBC]

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