How Do You Calculate the Wind Chill?

iStock/HelenL100
iStock/HelenL100

What does it really mean when my weatherman says that it feels like minus-20 in Chicago? Is there a wind chill thermometer somewhere, or is he just using a mathematical formula? Let's answer these and some of the other pressing questions about the ubiquitous winter statistic.

Why does wind make us feel cold?

When the wind blows across the exposed surface of our skin, it draws heat away from our bodies. When the wind picks up speed, it draws more heat away, so if your skin is exposed to the wind, your body will cool more quickly than it would have on a still day.

Who came up with the idea of calculating wind chills?

American explorer and geographer Paul Siple and his fellow explorer Charles Passel made the first breakthroughs in wind chill research while on an expedition in the Antarctic in 1940. Siple and Passel suspended bottles of water outside a hut at their base station and measured how long it took the water to freeze under various wind conditions. After taking hundreds of these readings, the pair had a good idea of how rapidly heat was lost at different wind speeds.

What exactly is a wind chill temperature?

When Siple and Passel did their research, they weren't really trying to develop a temperature equivalent that alarmist weathermen could trot out. In fact, their original measure expressed the heat loss in a more esoteric unit: watts per square meter.

The idea of expressing wind chills in terms of an equivalent temperature—the "feels like" language we hear on the news—didn't start until the 1970s. Before the switch, weathermen would report the wind chill in three- or four-digit numbers which were a bit difficult for viewers to wrap their heads around. American weathermen started translating wind chills into temperature equivalents in order to give viewers a more familiar term.

If the air temperature is 40 degrees but the wind chill is 28 degrees, will water freeze?

Nope. Although high winds can make those of us with a pulse feel more miserable than normal, they don't have the same effect on inanimate objects. Lower wind chills mean that inanimate objects cool to the air temperature more quickly, but even high winds can't force the object's temperature below the air temperature. That means that in the above example even though your skin might think it's 28 degrees, your water pipes will still be a balmy 40 degrees.

So is there an actual formula for wind chill?

You bet. Just in case you ever find yourself with a calculator, thermometer, and anemometer but without access to The Weather Channel, the Fahrenheit version of the equation looks like this:

Wind Chill = 35.74 + 0.6215T – 35.75(V^0.16) + 0.4275T(V^0.16)

T is the air temperature in degrees Fahrenheit, and V is the wind speed in miles per hour.

Wait, shouldn't how cold the wind makes you feel depend on all sorts of variables like your body type, and whether you're walking into the wind?

Those things certainly affect how quickly the wind cools a person's skin. The above formula makes some simplifying assumptions to get its numbers. Basically, the wind chill factor you hear reported assumes that your exposed face is roughly five feet off the ground, it's night, and you're walking directly into the wind in an open field at a clip of about 3 mph.

Are those conditions really all that realistic?

If you're in a profession that involves a lot of night-field-walking, sure. Otherwise, maybe not. Critics of wind chill reports note that lots of factors can mitigate the reported wind chill. Your weatherman may tell you that it feels like 50 below outside, but if you're dressed warmly, standing in the sun, or in an area with cover like buildings and trees that block the wind, you will feel significantly warmer.

So if the formula is arguably somewhat dubious, can we just disregard wind chill reports as frivolous statistics?

Not so fast. While the methodology concerning wind chill calculations is still being debated in some quarters, that doesn't mean that the measurements are altogether useless. Remember, the basic concept behind wind chill is that stronger winds will cause exposed skin to cool more quickly. The faster skin cools, the faster frostbite can set it. As wind chills drop south of -50 or so, the onset of frostbite can take as little as five minutes, so it's worth keeping an eye on the wind chill even if the notion of your skin "feeling like" a certain temperature may be a bit misleading.

Has the formula always been the same?

The above formula is actually a fairly new development that the National Weather Service introduced in late 2001. During the year 2000, the National Weather Service and its Canadian counterpart had independently started looking for ways to improve the wind chill formula, partially because they had a sneaking suspicion the old formula overstated just how cold it was. This overstatement may sound innocuous, but the weather services worried that it would lull citizens into a false sense of security if it led people to believe they could withstand colder temperatures than they realistically could.

Since the collaborating weather services knew that the old wind chill formula was broken—"feels like -50" actually felt much warmer than standing around on a windless 50-below day—they recruited a group of volunteers to walk on treadmills in a refrigerated wind tunnel. Using sensors on the subjects' skin, scientists calculated a more accurate formula. You can read one of the test subjects' thoughts on the experiments here.

What's the lowest wind chill ever recorded?

With all of the tweaks in the formula over the years, it's tough to say definitively, but how's this for chilly: on July 4, 2003, a remote weather station in east Antarctica picked up a minus-94 degree day. That would be plenty frigid on its own, but the wind was also blowing at 75 miles per hour, which would be good for a wind chill of about minus-150.

This post originally appeared in 2010.

Looking to Downsize? You Can Buy a 5-Room DIY Cabin on Amazon for Less Than $33,000

Five rooms of one's own.
Five rooms of one's own.
Allwood/Amazon

If you’ve already mastered DIY houses for birds and dogs, maybe it’s time you built one for yourself.

As Simplemost reports, there are a number of house kits that you can order on Amazon, and the Allwood Avalon Cabin Kit is one of the quaintest—and, at $32,990, most affordable—options. The 540-square-foot structure has enough space for a kitchen, a bathroom, a bedroom, and a sitting room—and there’s an additional 218-square-foot loft with the potential to be the coziest reading nook of all time.

You can opt for three larger rooms if you're willing to skip the kitchen and bathroom.Allwood/Amazon

The construction process might not be a great idea for someone who’s never picked up a hammer, but you don’t need an architectural degree to tackle it. Step-by-step instructions and all materials are included, so it’s a little like a high-level IKEA project. According to the Amazon listing, it takes two adults about a week to complete. Since the Nordic wood walls are reinforced with steel rods, the house can withstand winds up to 120 mph, and you can pay an extra $1000 to upgrade from double-glass windows and doors to triple-glass for added fortification.

Sadly, the cool ceiling lamp is not included.Allwood/Amazon

Though everything you need for the shell of the house comes in the kit, you will need to purchase whatever goes inside it: toilet, shower, sink, stove, insulation, and all other furnishings. You can also customize the blueprint to fit your own plans for the space; maybe, for example, you’re going to use the house as a small event venue, and you’d rather have two or three large, airy rooms and no kitchen or bedroom.

Intrigued? Find out more here.

[h/t Simplemost]

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7 Facts About the Hurricane Highway

Hurricane Earl (top) and Hurricane Fiona (bottom) pummel the U.S. coast and Caribbean islands.
Hurricane Earl (top) and Hurricane Fiona (bottom) pummel the U.S. coast and Caribbean islands.
NOAA/NASA GOES Project // Public Domain

Autumn is the peak of hurricane season, also known as Cape Verde season, after the islands where the so-called "hurricane highway" originates. Here are seven facts about this awesome—and sometimes deadly—weather phenomenon.

1. The hurricane highway begins near the African coast.

The Cape Verde Islands, located off the northwest coast of Africa, are where the hurricane highway starts. Thunderstorms destined to become hurricanes often form into a tropical depression near the islands, slowly organizing and strengthening over the following week as the system moves toward the Caribbean. These storms have a long time to get their act together, but they also have to cover a lot of distance without losing their power to reach the East Coast as a hurricane. Some storms are able to thrive with little wind shear, ample warm water, and moist air, while others starve and dissipate if they encounter cooler waters and strong winds, or ingest dry, dusty air blowing off the Sahara Desert.

2. An easterly jet stream gives rise to the hurricane highway.

It’s hard to imagine from North America that a couple of thunderstorms on another continent thousands of miles away can swirl up into a monstrous storm, but it happens almost every year. The extreme temperature gradient between the blistering heat of the Sahara Desert and the more temperate climate of the savanna to its south creates an easterly jet stream that triggers clusters of showers and thunderstorms. These clouds then move from east to west, emerging off the western African coast near the Cape Verde Islands. Every year, the right conditions turn a handful of these localized storms into tropical storms that make their way across the Atlantic.

3. The biggest hurricanes start with the smallest storms on the hurricane highway.

Hurricane Andrew was a Category 5 hurricane when it made landfall in Homestead, Florida.Xanxz/NOAA, Wikimedia Commons // Public Domain

Hurricanes, cyclones, typhoons—these are all names for the same force of nature, like Hurricane Andrew, which hit the East Coast in 1992. Cyclones like Andrew don’t just form out of thin air. All tropical cyclones require a relatively tiny “nucleus” of thunderstorms in order to develop. When the air and water temperatures are right, these groups of thunderstorms sometimes spin up into a fierce low-pressure system capable of causing a lot of damage. We see lots of these seedling thunderstorms over the ocean every year, but only a small number of them become hurricanes.

4. Hurricanes form in different places in different months.

Where a tropical storm or hurricane begins its trip across the ocean depends on what time of the year it forms. Storms that form early in the season usually get their start from thunderstorms or cold fronts that stall over the water very close to land; almost all of the storms that form in the Atlantic in June come to life within a few hundred miles of land. When we reach the peak of hurricane season, though, they start to form farther and farther out in the ocean—all the way out to the shores of Africa.

5. Fall is the peak of hurricane season on the hurricane highway.

Hurricane season in the Atlantic Ocean runs from June 1 through November 30. Storms are most common during that six-month stretch of the year, but sometimes they can form earlier or later too. That said, the period between the middle of August and the middle of October is typically the climatological peak of the season. That’s because, as the ocean water gets warmer, the atmosphere becomes conducive to vigorous storms, increasing the risk for hurricanes and tropical storms.

6. Cape Verde hurricanes can easily land in the record books.

This image shows the tracks of all tropical cyclones recorded in the Atlantic Ocean between 1851 and 2014.
Dennis Mersereau

Tropical waves traveling west from the coast of Africa in the middle of the summer are the culprits behind some of the worst hurricanes we’ve experienced in the United States. For example, on August 8, 2005, a small tropical wave emerged off the coast of Africa, soon becoming Tropical Depression 10. That depression would fall apart a few days later, but its remnants kept moving toward the U.S., redeveloping into a new tropical depression over the Bahamas on August 23. That new tropical depression became Hurricane Katrina, the costliest hurricane to ever strike the United States.

It’s a similar story for many—but not all—major hurricanes in recent history. Hurricanes Andrew, Dennis, Ivan, Isabel, and Ike were all Cape Verde–type storms that sprang to life thousands of miles away from where they would ultimately wreak havoc.

7. Strong hurricanes can still form in other places in autumn.

While the far eastern part of the Atlantic Ocean is a hotbed of activity this time of the year, it’s not the only place you need to watch if you live near the coast. Storms that form close to land can quickly spin themselves into catastrophe. Hurricane Sandy formed just south of Jamaica and hit New Jersey in a matter of days in 2012. A tropical depression that developed east of Florida on September 18, 2005, exploded into Hurricane Rita just three days later, with 180 mph winds—the most intense storm ever recorded in the Gulf of Mexico.

Meteorologists are currently predicting an above-average hurricane season in 2020. It may be worth preparing: NOAA suggests gathering a few key disaster supplies to have on hand, getting an insurance check-up, and locating the safest high ground.