9 Powerful Facts About Derechos

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iStock

Think about the worst thunderstorm you've ever witnessed. Having trouble remembering the specifics? That's because in the summertime, thunderstorms are a relatively mundane occurrence, even for those of us with a flair for exaggeration. There are some storms, though, that rise to a whole new level; a derecho is one of those storms. Derechos can sweep across entire states and leave behind more damage than a tornado, yet they're relatively unknown by anyone other than weather enthusiasts.

1. DERECHOS ARE MASSIVE.

A squall line or bow echo is a group of thunderstorms that are connected to one another and take on a bow-shaped look on weather radar. A squall line that forms under the right conditions can mature into a small but powerful storm system in its own right, developing tiny high- and low-pressure centers that can help drive the thunderstorms for hundreds of miles.

Weather radar showing a derecho, or squall line, in Missouri
A radar image of an intense derecho in Missouri on May 8, 2009.
Gibson Ridge

A derecho is a long-lived squall line that produces a swath of wind damage more than 200 miles long. People who go through derechos sometimes compare them to hurricanes because of the strength of the winds and the amount of damage they leave behind. The term derecho, pronounced “duh-RAY-cho,” comes from the Spanish word for “straight,” a reference to the winds that make these storms so powerful.

All derechos are squall lines, but not all squall lines turn into derechos. The term derecho only applies when large amounts of land area see damage from a storm. But regular squall lines are nothing to sneeze at: A system that only affects three counties can be just as strong as one that affects three states.

2. DERECHOS GET THEIR BITE FROM COLD AIR.

What distinguishes a squall line from a normal thunderstorm is how the updraft and downdraft develop. The thunderstorms in a squall line form along the leading edge of the pool of cold air dragged to the ground by the downdraft. This dome-shaped cold pool tilts the updraft of warm, unstable air, preventing the updraft from suffocating on cool air. Air inside the cold pool beneath the storms can begin to circulate due to upper-level winds and friction with the ground, creating a dangerous feature called a rear-inflow jet. This jet of strong winds forms a few thousand feet above the ground and races toward the front of the thunderstorms, where it's shoved into the ground at the leading edge of the squall line, creating a derecho's signature winds.

3. STRAIGHT-LINE WINDS MAKE THEM DANGEROUS.

Tornadoes get all the attention during storm season, but the truth is that straight-line winds can cause just as much damage as a tornado, but over a much wider area than a tornado could ever cover. Just as the name suggests, straight-line winds hit the ground and move in the same direction, sometimes blowing for more than five minutes. The sudden impact and long duration of these winds can put serious stress on trees, buildings, and anything not tied down to the ground.

4. A DERECHO CAN CAUSE AS MUCH DAMAGE AS A TORNADO.

The aftermath of many derechos looks like what you'd see after a hurricane makes landfall. Some people even swear that they were hit by a tornado, not believing that a severe thunderstorm could make that big of a mess. The straight-line winds in a derecho can climb as high as 100 mph—strong enough to rip the roofs off of homes and completely destroy structures like barns and silos. Even a derecho that just barely qualifies as one can leave behind thousands of downed trees, long-lasting power outages, and annoying and costly cosmetic damage to homes and businesses.

5. SOME ARE MORE SERIOUS THAN OTHERS.

There are two different types of derechos. The most dangerous type is a progressive derecho. This is the kind of storm you see in the summer that speeds across entire states and leaves tornado-like damage in its wake. A serial derecho forms along a cold front. What a serial derecho lacks in focused damage it can make up for in the sheer amount of land exposed to severe wind gusts. It's possible for the length of a serial derecho to stretch from the Great Lakes to the Gulf of Mexico as it moves from west to east. Serial derechos are most common during the fall and winter months.

6. HEAT WAVES BREED DERECHOS.

A relentless summertime heat wave can trigger multiple derechos in one week if conditions are just right. A high-pressure system that causes a brutal heat wave during the summer is sometimes called a “ring of fire” by meteorologists. The northern edge of one of these hot high-pressure systems can serve as the point for a progressive derecho to form. Once the derecho has developed, it races east or southeast along the outer edge of the high-pressure system until it dissipates or reaches the Atlantic Ocean.

7. THE CLOUDS CAN LOOK TERRIFYING.

The ominous clouds ahead of a derecho can tell you pretty quickly that this is no ordinary storm headed your way. Derechos are home to the most incredible shelf clouds nature can produce. A shelf cloud is a thick cloud that juts down from the sky, like a shelf hanging beneath the bottom of the storm. These clouds form when warm air rises up and condenses over the top edge of the cold pool that drives these storms. Shelf clouds are quite common, but the vivid shelf clouds in derechos are a spectacular, albeit scary, sight to see.

8. THE WIND COMES ON SUDDENLY.

One of the reasons derechos (or any intense squall line, really) can wreak such havoc is because they come on suddenly. There usually isn't much of a buildup to the strongest winds before they hit. Conditions can go from calm to chaos in a matter of seconds. The abruptness with which the winds can hit can even snap off the tops of trees as if they were chopped down by hand.

9. THERE ARE A FEW DERECHOS EVERY YEAR.

Derechos are most common in the central United States, but they can form just about anywhere around the world that experiences severe thunderstorms. Most derechos go unnoticed by those not directly affected by the storm, but some can have such a large impact on populated areas that they make national news.

One such storm was the derecho that formed on June 29, 2012. The storms started in Indiana, grew into a monstrous squall line in Ohio, and blew across the Appalachian Mountains virtually unimpeded before continuing on to the Atlantic Ocean. The Storm Prediction Center received hundreds of reports of wind damage after the storm. Washington D.C. and its suburbs were particularly hard-hit by the storm's winds. The derecho left millions without power, some for weeks after the storm, and multiple people lost their lives as a result of falling trees.

12 Powerful Facts About Hurricanes

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iStock/shaunl

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.

Denver is About to Experience Summer and Winter Temperatures Within 24 Hours

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iStock.com/mphotoi

In a story tailor-made for exhaustive Weather Channel coverage, Denver, Colorado is about to experience one of the more bizarre weather shifts in recent memory. After an expected Tuesday high of 80°F, residents can anticipate a dramatic shift down to 32°F by midday Wednesday, with an initial half-inch of snow accumulation increasing to up to 7 inches by Wednesday night.

Put another way: Citizens who need to make sure they hydrate in the warm temperatures Tuesday will have to bring out the parkas the following day.

The Denver Post reports that the warm air coming ahead of the cold can result in a clash of air masses, prompting areas of low pressure that can create forceful and damaging weather conditions. The storm could bring winds of up to 60 miles per hour and possibly even cause power outages. Snow accumulation should dissipate by the weekend, when temperatures are expected to climb back into the 60s.

The high temperature record for April 9 in Denver is 81°F, set in 1977.

[h/t The Denver Post]

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