How Do You Calculate the Wind Chill?


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.

Colorado Welcomed Summer With 2 Feet of Snow

Emmanuel Dunand/AFP/Getty Images
Emmanuel Dunand/AFP/Getty Images

While people in some parts of the country celebrated the first day of summer with barbecues and trips to the beach, residents of north and north-central Colorado had a snow day. Areas west of Denver—including Grand Lake, Aspen, and Steamboat Springs—experienced snow storms on summer solstice, with snowfall totaling nearly 2 feet at the highest elevations, CBS Denver reports.

Snow started falling in the Rocky Mountains the morning of Friday, June 21 and continued Sunday. Areas at ground level weren't cold enough to experience the unusual weather, but at elevations of 7000 feet and above, it looked like a winter wonderland. Steamboat Springs, a ski resort town in Colorado’s Yampa Valley, accumulated 20 inches of snow on the longest day of the year.

While Colorado mountain towns are used to seeing snow at odd times of year, the weekend's weather was still out of the ordinary. The average snowfall for Steamboat Springs in June is 0.1 inches. Prior to last Friday, it had been 91 years since a snowstorm hit the city in late June.

Snow has fallen in the Rockies later than average in six out of the past seven years. Though it feels like an extension of winter, the trend may actually be a product of the warming atmosphere. A warmer climate affects the jet stream, potentially pushing its course further south and leading to unusual weather patterns, such as unseasonable snowstorms in Colorado.

That means residents of some parts of the state will have to wait to have their summer hikes and picnics. The weather was serious enough to shut down one road in Rocky Mountain National Park.

[h/t CBS Denver]

12 Powerful Facts About Hurricanes


Hurricanes are a stunning, and dangerous, display of nature’s power. They’re some of the largest and most intense storms nature can produce. Today, we know more about these systems and have an easier time measuring and predicting them than ever before. There’s more than meets the eye when it comes to hurricanes. As the 2019 hurricane season kicks off (it runs from June 1st through November 30th), here are some things you might not know about these dangerous storms.

1. Hurricanes are only "hurricanes" around North America.

A tropical cyclone is a compact, low-pressure system fueled by thunderstorms that draw energy from the heat generated by warm ocean waters. These tropical cyclones acquire different names depending on how strong they are and where in the world they form. A mature tropical cyclone is called a hurricane in the Atlantic and eastern Pacific Oceans. What’s known as a hurricane in the Atlantic is called a typhoon near Asia and simply a cyclone everywhere else in the world.

2. Hurricanes come in all shapes and sizes.

Not all hurricanes are picture-perfect. Some storms can look so disorganized that it takes an expert eye and advanced technology to spot them. A full-fledged hurricane can be as small as a few dozen miles across or as large as one-half of the United States, as was the case with Typhoon Tip in the western Pacific Ocean in 1979. The smallest tropical cyclone on record was 2008’s Tropical Storm Marco, a tiny storm in the Gulf of Mexico that almost made it to hurricane strength. Marco’s strong winds only extended 12 miles from the eye of the storm—a distance smaller than the length of Manhattan.

3. The greatest danger in a hurricane is in the eyewall.

The spiraling bands of wind and rain that radiate from the center of a hurricane are what give these storms their distinctive buzzsaw shape. These bands can cause damage, flooding, and even tornadoes, but the worst part of a hurricane is the eyewall, or the tight group of thunderstorms that rage around the center of the storm. The most severe winds in a hurricane usually occupy a small part of the eyewall just to the right of the storm’s forward motion, an area known as the right-front quadrant. The worst damage is usually found where this part of the storm comes ashore.

4. The eye of a hurricane is very warm.

The core of a hurricane is very warm—they are tropical, after all. The eye of a hurricane is formed by air rushing down from the upper levels of the atmosphere to fill the void left by the low air pressure at the surface. Air dries out and warms up as it rapidly descends through the eye toward the surface. This allows temperatures in the eye of a strong hurricane to exceed 80°F thousands of feet above the Earth's surface, where it’s typically much colder.

5. You can tell a lot about a hurricane by its eye.

Like humans, you can tell a lot about a hurricane by looking it in the eye. A ragged, asymmetrical eye means that the storm is struggling to strengthen. A smooth, round eye means that the storm is both stable and quite strong. A tiny eye—sometimes called a pinhole or pinpoint eye—is usually indicative of a very intense storm.

6. Some hurricanes have two eyes.

An eye doesn’t last forever. Storms frequently encounter a process known as an “eyewall replacement cycle,” which is where a storm develops a new eyewall to replace the old one. A storm weakens during one of these cycles, but it can quickly grow even more intense than it originally was once the replacement cycle is completed. When Hurricane Matthew scraped the Florida coast in October 2016, the storm’s impacts were slightly less severe because the storm underwent an eyewall replacement cycle just as it made its closest approach to land.

7. The strong winds that a hurricane creates are only part of the danger.

While strong winds get the most coverage on the news, wind isn’t always the most dangerous part of the storm. More than half of all deaths that result from a landfalling hurricane are due to the storm surge, or the sea water that gets pushed inland by a storm’s strong winds. Most storm surges are relatively small and only impact the immediate coast, but in a larger storm like Katrina or Sandy, the wind can push deep water so far inland that it completely submerges homes many miles from the coast.

8 California rarely sees tropical cyclones.

It can seem odd that California occupies hundreds of miles of coastline but always seems to evade the hurricane threat faced by the East Coast. California almost never sees tropical cyclones because the ocean is simply too cold to sustain a storm. Only a handful of tropical cyclones have ever reached California in recorded history—the worst hit San Diego in 1858. The San Diego Hurricane was an oddity that’s estimated to have reached category 1 intensity as it brushed the southern half of the Golden State.

9. Hurricane hunters fly planes into storms.

Aside from satellite and radar imagery, it’s pretty hard to know exactly what a hurricane is doing unless it passes directly over a buoy or a ship. This is where the Hurricane Hunters come in, a brave group of scientists with the United States Air Force and NOAA who fly specially outfitted airplanes directly into the worst of a storm to measure its winds and report back their findings. This practice began during World War II and has become a mainstay of hurricane forecasting in the decades since.

10. Hurricane hunters drop sensors to measure waves.

The Hurricane Hunters assess the storm with all sorts of tools that measure temperature, pressure, wind, and moisture, and have weather radar onboard to give them a detailed view of the entire storm. They regularly release dropsondes to "read" the inside of the storm. Dropsondes are like weather balloons in reverse: instead of launching weather sensors from the ground into the sky, they drop them down through the sky to the ground. The Hurricane Hunters also have innovative sensors that measure waves and sea foam and use the data to accurately estimate how strong the winds are at the surface.

11. We started naming storms to keep track of them.

Meteorologists in the United States officially started naming tropical storms and hurricanes in the 1950s to make it easier to keep track in forecasts and news reports. Since then, naming tropical cyclones has become a worldwide effort coordinated by the World Meteorological Organization, the United Nations agency responsible for maintaining meteorological standards. Today, the Atlantic Ocean and eastern Pacific Ocean each receive a list of alternating masculine and feminine names that are reused every six years.

12. Names are retired if the storm was especially destructive.

If a storm is particularly destructive or deadly, the WMO will “retire” the name from official lists so it’s never used again out of respect for the families of the storm’s victims and survivors. When a name is retired, another name starting with the same letter takes its place. More than 80 names have been retired from the Atlantic Ocean’s list of names since 1954. Earlier this year, it was announced that the names Florence and Michael were being retired as a result of the damage they caused during the 2018 hurricane season; they will be replaced with Francine and Milton when the list is reused in 2024.

This piece originally ran in 2017; it has been updated for 2019.