A deep dive into the powerful 2015 tornado that destroyed Fairdale, Illinois

A devastating EF-4 tornado carved a scar through 30 miles of farmland in north-central Illinois on a muggy afternoon in April 2015. Two people died and nearly a dozen more were injured as the storm levelled neighborhoods in Rochelle and Fairdale, about an hour's drive west of Chicago.

Estimated winds reached 200 mph as the tornado swept homes and businesses clean off their foundations. Falling just 1 mph shy of scale-topping EF-5 status, it stands in the records at the strongest tornado to hit Illinois that decade. 

Here's an in-depth look at how a modest rain shower grew into a killer supercell over the course of just two hours.

Note: This is an adaptation of an article I originally wrote for The Vane on April 14, 2015. Since neither Gawker nor The Vane exist anymore (outside of the Internet Archive), I'm reworking and publishing this article by popular request.

A Volatile Setup

We saw a classic springtime severe weather event unfold across the central U.S. during the second week of April 2015.

A strong trough diving over the Rockies spawned a low-pressure system over eastern Colorado on Wednesday, April 8, leading to a multi-day severe weather outbreak across the Plains and Midwest states.

This system was in its prime as it arrived in eastern Iowa during the day on Thursday, April 9. The air certainly had that stormy 'feel' to it on Thursday afternoon as southerly winds dragged warm, muggy air over Illinois—providing plenty of instability and moisture for thunderstorms to thrive.

A mile or two above the surface, southwesterly winds were racing along at highway speeds as air whipped around the strengthening low-pressure system. Even higher in the atmosphere—about five miles up—winds were blowing out of the west at nearly 100 mph. 

Wind shear is a critical factor in pushing ordinary thunderstorms beyond severe limits. This sharp change in wind speed and direction with height creates a horizontal rolling motion in the atmosphere. A thunderstorm's strong updraft can force this horizontal rotation to tilt vertically, allowing the updraft to 'absorb' the rotation (so to speak). 

A thunderstorm with a rotating updraft is called a supercell. Rotation makes a supercell's updraft stronger and more resilient than an ordinary thunderstorm, creating a storm that can last longer, travel farther, produce bigger hail, and spawn tornadoes.

Particularly intense supercells are capable of supporting the strongest tornadoes ever observed. These high-end twisters can grow more than a mile wide, packing winds close to 200 mph as they carve a path dozens and even hundreds of miles long.

The supercell that tore through north-central Illinois on April 9, 2015, was one of those storms.

5:34 p.m. CDT

Unstable air rapidly rising into the atmosphere about 70 miles southwest of Fairdale generated a vigorous batch of billowing cumulus clouds.

The weight of the water overpowered the strength of the updraft, falling to the ground as the first detectable batch of light rain just south of the town of Annawan.

5:48 p.m. CDT | Elapsed Time: 14 minutes

It took less than fifteen minutes for the shower to grow into a downpour as the thunderstorm kicks into gear. We can already see the storm taking on the vague outline of a supercell's classic shape.

Wind shear is tilting the storm's updraft toward the northeast, forcing the rain-cooled air in the downdraft to flow around the western side of the storm—a feature known as a rear-flank downdraft. This setup allows the storm to vent its rain-cooled air without interrupting the warm, unstable air feeding into the downdraft. 

5:59 p.m. CDT | Elapsed Time: 25 minutes

By the top of the hour, the storm is rapidly maturing into a full-blown supercell.

The warm, unstable air streaming into the updraft leaves a precipitation-free vault in the base of the storm known as an inflow notch. We can see the rear-flank downdraft wrapping around the western side of the storm. These two features help generate the classic hook echo that make supercells so ominously recognizable on radar imagery.

However, supercells really thrive when they're all alone. Another thunderstorm that bubbled up a few miles to the west is interfering with its development. The storm will struggle to reach its full potential until the neighboring storm dissipates or moves away.

6:08 p.m. CDT | Elapsed Time: 32 minutes

Eight minutes after the hour, the supercell's appearance is already improving as the neighboring storm starts to pull away. We can see the beginnings of a hook echo showing up on precipitation and velocity (wind) imagery.

The storm is starting to develop a "v-notch" as strong winds aloft deflect around the updraft like water around the bow of a boat, leaving something of a rain-shadow effect immediately downwind from the updraft. 

6:11 p.m. CDT | Elapsed Time: 34 minutes

Forecasters issue a severe thunderstorm warning for large hail and damaging winds.

6:27 p.m. CDT | Elapsed Time: 52 minutes

The leading edge of the supercell approaches Rochelle, Illinois, and its population of about 10,000 residents. A well-defined hook echo is present on radar now, a sign that rotation within the storm is rapidly tightening up as the supercell takes advantage of the favorable environment.

6:35 p.m. CDT | Elapsed Time: 1 hour, 1 minute

Forecasters at the National Weather Service in Joliet issue a tornado warning based on the strong rotation indicated by radar imagery.

A 3-D rendering of the supercell shows the powerful mesocyclone stretching from the base of the storm up beyond the cruising altitude of passenger jets—indicative of a very healthy and very hazardous supercell.

6:47 p.m. CDT | Elapsed Time: 1 hour, 12 minutes

One of the great benefits of modern weather radar is that we don't always have to wait for visual confirmation to know that a storm is producing a tornado.

Tornado debris reflects a significant amount of radiation back to the radar site. This return often shows up as a dark circle—called a debris ball—that coincides with the location of strong rotation within the storm.

A (then-recent) radar upgrade called dual polarization allows us to see the size and shape of the objects reflecting the radar beam, which is useful for telling rain, hail, and debris apart. A big mix of different sizes and shapes will show up with a low correlation coefficient. The data left no question that this is a significant amount of debris lofting into the atmosphere.

6:57 p.m. CDT | Elapsed Time: 1 hour, 22 minutes

This large, wedge tornado is now at its peak intensity as it spares Rochelle by tracking just west and north of the town center.

The most intense damage occurs along S Richard Road and E Kuehl Court, just northwest of Rochelle. Several homes on these roads were completely levelled, with wind-swept debris tossed a significant distance downwind from each residence. Surveyors used this damage to rate the tornado a high-end EF-4, just one tick below EF-5 strength.

Just north of Rochelle, though, a restaurant called Grubsteakers takes a direct hit from the tornado. Thanks to advanced warning—the tornado warning has been in effect for 23 minutes at this point—all 12 people in the building escaped injury by huddling in the restaurant's cellar.

Grubsteakers was a total loss, but it didn't take the full brunt of this powerful tornado.

Surveyors found EF-4 damage just a short walk north of Grubsteakers, where the tornado destroyed a home, scrubbed a barn down to its foundation, and debarked sturdy trees on the property.

7:00 p.m. CDT | Elapsed Time: 1 hour, 25 minutes

An exceptionally clear view of the tornado from the south allows multiple storm chasers and residents to capture crisp images of the storm as it passes through the area.

After hitting properties north of Rochelle, the tornado spent the next several minutes passing over farmland. Multiple homes and structures suffered damage, with surveyors finding EF-2 to EF-3 damage in a few spots.

Satellite imagery taken a few days after the storm revealed a remarkable pattern of cycloidal marks carved into the topsoil along the tornado's visible scar. Large tornadoes often contain multiple vortices swirling around the larger overall circulation. The vortices, as well as any debris caught in them, can gouge the ground in swirling patterns that are easily visible from the air after the storm.

7:13 p.m. CDT | Elapsed Time: 1 hour, 38 minutes

Fairdale takes a direct hit.

The tornado carved through the northwest corner of this 0.08-square-mile community, destroying more than a dozen homes and damaging just about every building in town.

Two people died and 22 more were injured in the few seconds it took for the tornado's intense winds to rip through Fairdale. One resident in the path of the storm filmed the tornado from a window as it approached the community; his wife died and he was injured when the storm destroyed their home. 

Ground surveys and satellite imagery reveal the extent of the damage. Extensive ground scouring, debarked trees, and near-complete destruction of all structures and vehicles left the northwestern corner of Fairdale unrecognizable. 

7:27 p.m. CDT | Elapsed Time: 1 hour, 52 minutes

Past its prime, the large supercell that produced the Fairdale tornado is in the waning stages of its life.

The supercell is beginning to merge into the squall line chugging through northern Illinois, which brought rough weather to the city of Rockford just a few minutes earlier. Rain-cooled air and the nearby thunderstorms are disrupting the supercell's structure, forcing it to break down.

7:50 p.m. CDT | Elapsed Time: 2 hours, 16 minutes

Just over two hours after a tiny shower in central Illinois grew into a supercell that dropped a violent tornado, the storm has fully absorbed into the squall line and is no longer its own, independent storm.

Animation

One of the most striking aspects of the storm was how the violent tornado itself developed.

If we animate the radar at the storm's peak strength, we can see that a tiny shower ingested into the inflow that fed the storm its supply of unstable air. There have been plenty of similar cases over the years where a nearby shower or thunderstorm brushes past or gets ingested into the hook of a supercell thunderstorm, enhancing the spinning and stretching motions needed to spawn a powerful tornado.

This tragic event provided a remarkable opportunity to watch the evolution of a destructive thunderstorm from infancy to dissipation. It's sometimes easy to forget that even the mightiest storm begins as a single puffy cloud. 

[Top image courtesy of the NWS. All radar images courtesy of Gibson Ridge and compiled/annotated using Canva.]

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A Powerhouse Supercell Managed To Travel 300 Miles Across Three States

A real powerhouse of a supercell thunderstorm rolled across hundreds of miles of southern woodlands on Wednesday evening, ramping up in east-central Texas on Wednesday afternoon before finally petering out nearly eight hours later over the Mississippi River near Natchez, Mississippi. The supercell produced multiple tornadoes along its path, even prompting a tornado emergency as it approached Fort Polk, Louisiana.

Wednesday saw a classic springtime severe weather event across the southern Plains and lower Mississippi Valley. A line of tornadic supercells developed along a dry line in central Oklahoma, including a tornado that killed two people and grew to frightening strength in a matter of seconds.


The environment was just as ripe for severe weather farther to the south in Texas. A single supercell managed to survive for eight hours as it tracked from College Station, Texas, to Natchez, Mississippi. The video above shows a radar loop (video by me, radar by College of DuPage) of the storm along its track from College Station to Natchez. It's the southernmost storm that begins on the bottom-left and ends just right of center in the frame.

The thunderstorm near College Station that'd grow into the long-track supercell. (Gibson Ridge)

A thunderstorm began to develop broad rotation near College Station, Texas, around 3:00 PM CDT, slowly growing more organized over the next couple of hours as it moved east of the town. Things got going in a hurry as the supercell moved south of Lufkin, Texas, around 5:30 PM CDT, producing the first in a series of tornadoes that would touch down between there and central Louisiana through the evening.

A tornado east of Jasper, Texas. (Gibson Ridge)

The supercell neared peak strength once it got into far eastern Texas, cycling through stronger and weaker phases as it moved into Louisiana. The radar image above shows the storm around 7:30 PM CDT, as it approached the Texas/Louisiana border. It's broken down into four panels:

• The top-left panel shows reflectivity, or precipitation.
• The top-right panel shows velocity, or wind. Green shows wind blowing toward the radar (to the east), while red shows wind blowing away from the radar. When you have a strong, tight cluster of red and green right next to each other, it shows strong rotation within a storm.
• The bottom-left panel shows correlation coefficient. The radar beam can tell us how similar in shape and size the objects are that it's intercepting. Uniform objects like raindrops have a high correlation coefficient (red/purple), while mismatched objects like tornado debris have a very low correlation coefficient (blue). When you see a dark blue dot in the same spot as tight rotation, you're looking at debris swirling around a tornado.
• The bottom-right panel is normalized rotation, or NROT. This is an algorithm within Gibson Ridge's radar program that helps you quickly spot areas of rotation. Higher NROT values can indicate stronger rotation.

A tornado approaching Fort Polk, Louisiana, on April 22, 2020. (Gibson Ridge)

This storm appears to have produced several strong tornadoes across eastern Texas and central Louisiana. The National Weather Service in Lake Charles, Louisiana, had to issue a tornado emergency for Fort Polk, a military training site that houses thousands of troops and their families, as a confirmed tornado moved very close to the heart of the base.

The storm continued producing possible tornadoes as it passed southeast of Alexandria, Louisiana, before the updraft weakened and the storm finally started falling apart as it crossed the Mississippi River south of Natchez, around 11:00 PM CDT. The storm powered along almost uninterrupted for eight hours (!!!) before it finally fell apart.

A supercell is powered by a rotating updraft. Strong wind shear can cause horizontal rolling motions in the atmosphere. If a strong thunderstorm can develop in that environment, the updraft will push that rotation into the vertical and the updraft itself will begin to rotate. This rotating updraft then tilts downwind, allowing the storm to ingest unstable air and vent cooler air without choking itself off like a "normal" thunderstorm would.

This was a rather unusual testament to the endurance of a supercell when it's in a near-pristine environment. We usually don't see this kind of a marathon run outside of major outbreaks.

We're used to hearing about supercells after a tragic tornado or major hailstorm, but the vast majority of supercells are relatively—relatively—weak and don't last for very long. Supercells can be extremely fragile, falling apart if their outflow moves too quickly or if nearby storms contaminate the environment ahead of them with stable air. It's quite something to watch a supercell on radar practically disappear in just a few frames.  But there was nothing in this storm's way and it took full advantage of the situation.

Update: I changed the headline from "Tornadic Supercell Travels Farther In One Day Than You've Gone In The Last Two Months" to "A Powerhouse Supercell Supercell Managed To Travel 300 Miles Across Three States" because...well, do I really need to explain? 

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A Meteorologist's Nightmare: A Strong Tornado Struck Downtown Nashville After Midnight

Nashville lived through a nightmare early Tuesday morning as a strong tornado struck the city’s core in the middle of the night. The tornado—or tornadoes, if there were several along a path—touched down west of Nashville after midnight and likely continued well to the city’s east, killing at least nine people and damaging hundreds of homes and businesses. The tornado was strong enough to loft debris thousands of feet into the air just as it began moving over the heavily populated downtown core.

The long-lived supercell began in west-central Tennessee and moved toward the Nashville region around midnight. The Storm Prediction Center issued a tornado watch for central Tennessee at 11:20 PM CST as they watched the supercell move toward the area. (Yes, they really do issue watches for single thunderstorms, and for good reason!)

The National Weather Service issued a severe thunderstorm warning for Nashville and surrounding areas at 12:11 AM. The supercell’s well-defined hook echo tightened up considerably as it approached Nashville proper, prompting a tornado warning at 12:35 AM. Debris began showing up on radar within a few minutes, and a debris ball was clearly visible on radar a few miles northwest of Nashville by 12:38 AM (shown in the screenshot at the top of this post). The fast-moving tornado struck the north side of downtown Nashville at about 12:42 AM, continuing east of the city over the next hour.

An employee of NWS Nashville caught video of the rain-wrapped tornado as it moved through the city’s core. It’s hard to see the tornado as it’s obscured by rain and the dark of night, but power flashes caused by transformers failing in the strong winds make the path easily traceable as it races through town.

The supercell that spawned the tornado (or tornadoes) is an example of how it only takes a brief moment of the right ingredients coming together to create an exceptionally dangerous situation. The SPC’s discussion of the tornado watch mentioned how the storm “may maintain its organization in a marginally favorable low-level air mass for a few hours before weakening.” It sure did. The supercell found just enough instability and low-level wind shear along a surface boundary north of Nashville to spin up a strong tornado. 

Meteorologists will survey the damage on Tuesday and issue a preliminary rating based on the damage they find.

The very situation that played out in central Tennessee last night is one of the scenarios that keeps meteorologists and emergency managers awake at night. A tornado approaching a city center is terrifying any day, but a strong, fast-moving tornado at 12:30 in the middle of the night is near the top of the list when it comes to dangerous situations.

Severe weather is possible across parts of the southern U.S. over the next couple of days. As we head through this period of active weather—and start climbing toward the peak of springtime severe weather—it’s important that you have multiple ways to receive severe weather warnings. You don't want to get caught off guard by a storm anytime, but especially at night when you're tuned-out or asleep.

Make sure your cell phone is set to receive Wireless Emergency Alerts for tornado warnings. Spring a few bucks for a programmable NOAA Weather Radio if you can. It may seem redundant or outdated given all the technology we have now, but phones and weather apps don’t always work. It’s good to have a backup.

[Screenshot: Radarscope]

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A Rare Tornado Hit A Small Town In Northern Canada, One Of Only 4 Recorded So Far North

A tornado struck a tiny town in northern Canada’s vast wilderness on June 2. The tornado damaged homes and businesses in Fort Smith, Northwest Territories, leaving residents shocked by the storm that just hit them. Tornadoes are rare at such a high latitude, and it’s even more rare that the tornado managed to hit such an isolated community.

Environment Canada confirmed that an EF-1 tornado touched down in Fort Smith on the afternoon of June 2, causing some structural damage and bringing down trees and power lines. Photos obtained and posted by CBC North show significant tree damage, crushed vehicles, and what appears to be a metal shed that was tossed and smashed in someone’s yard.

Residents in this part of the country have no reliable way to know a tornado is coming unless they see it for themselves. Environment Canada only has 31 weather radar sites set up across the country, centered on population centers near the southern border and in parts of the tornado-prone Prairie provinces. The nearest weather radar to Fort Smith is more than 350 miles away—that’s like using the radar at Washington’s Dulles Airport to see a storm over Providence, Rhode Island. This leaves folks up north to rely on satellite imagery or old-fashioned sky watching to stay ahead of an approaching thunderstorm.

Folks in Fort Smith probably never thought they'd see a tornado there. Tornadoes are extremely rare this far north. This is reportedly only the fourth tornado on record to strike Northwest Territories. It’s possible there are more tornadoes than we realize in interior and far-northern Canada, but communities are so few and far between that it takes a direct strike like we saw in Fort Smith for a tornado confirmation.

Tornado data maintained by Environment Canada shows more than 1,800 confirmed tornadoes across the country between 1980 and 2009, mostly focused around populated areas where people are actually around to witness tornadoes. Most tornadoes in Canada are relatively weak, though some tornadoes on the Prairies and in southern Ontario have been quite strong. The strongest tornado in Canadian history was an EF-5 that hit Elie, Manitoba, on June 22, 2007.

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The 1999 Okla. Tornado Sticks With Us Because It Was Our First Immersive Weather Disaster

Twenty years ago today, a mile-wide tornado touched down in central Oklahoma and forever changed the way Americans viewed severe weather. The F5 tornado was so strong and so destructive that it's served as a benchmark for all tornadoes since. People who otherwise wouldn't pay any mind to the weather, even people who live thousands of miles away from Oklahoma, can usually recall that one storm because it was our nation's first experience with the shock of fully immersing ourselves in the scope and power of a natural disaster.

24/7 news fundamentally changed the way we process emergency situations in faraway places. When we watch a disaster unfold on television or online, we're not watching something that already happened. We're taking in the disaster before we know the outcome. You can flip on any news channel and hear the screams and the gunshots and see the fireballs and the towers fall and monitor live footage from storm chasers who follow so close to the tornado that you can practically see the occupants of newly-destroyed houses getting pelted by their shredded living rooms if you look hard enough.

It's like you're right there as it happens, and that leaves a mark.

YouTube

The tornado in 1999 turned into a national trauma because we saw it happen live and you could relive the storm from every possible angle. A news helicopter chasing the tornado hovered over leveled homes before the people inside had a chance to crawl out of the debris. Live footage from the ground showed a mile-wide wedge of darkness tearing into neighborhoods like a desk fan through playing cards. A news station's chief meteorologist sternly told viewers that they needed to be underground to survive the storm while the television screen showed neighborhoods so freshly destroyed that the debris hasn't stopped falling from the sky yet.

The Bridge Creek-Moore tornado was a horrific storm that's served as the high water mark for every tornado in the 20 years since that day. It was one of the strongest tornadoes on record and it was one of the deadliest tornadoes ever recorded in Oklahoma. And it was the first time many Americans actually saw what happens when a tornado hits your house rather than just seeing footage and photos of the aftermath. It took the curiosity spawned by the movie Twister three years earlier and made it real and personal. That could really happen. And it's stuck with us for the last two decades.

There had been big natural disasters before. Hurricane Andrew was a seminal moment in hurricane history that you could watch unfold on The Weather Channel. But up to that point, we'd only had piecemeal footage of large-scale natural disasters, and usually well after the fact. Most of the scale-topping tornadoes since the Super Outbreak of 1974 were filmed or photographed from a great distance. At the time, the 1999 tornado was likely was the most documented tornado in history. There are dozens, if not hundreds, of recordings both from a distance and right within the tornado itself.

See Also: Living With Storm Anxiety As a Weather Geek

Every national tragedy sparks those "where were you" conversations. Where were you when you heard Kennedy was shot? Where were you when you heard the planes crashed? We don't have to ask that anymore because we're always there now. Modern technology allows us to experience the psychological trauma of every attack or shooting or tornado or hurricane from every angle as it unfolds. The tornado in 1999—occurring at a time when camcorders were ubiquitous, documentaries were a mainstay on cable TV, and right in the middle of the internet boom—was the first of countless tornadoes to have been documented in such fine detail that you can watch it as if you were standing right there.

We've had plenty of tornadoes like this in the last 20 years. The tornado outbreak of April 2011 was documented in frightening detail. The tornado in Joplin, Missouri, just a month later was so ruinous that it leveled every building as far as the eye could see. And there was another EF-5 tornado in Moore, Oklahoma, that left behind similar death and destruction with even greater documentation than the storm 14 years earlier. Those tornadoes are all memorable, but none so memorable for so many people as the F5 tornado that touched down on May 3, 1999. That storm 20 years ago today was our first full experience with this new era of watching the weather. And it was terrifying.

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Deadly Alabama Tornado Tests The Boundaries Of Advanced Tornado Warnings

A significant tornado outbreak in the southeastern United States on Sunday killed at least 23 people despite hours of advanced warning that dangerous storms were on the way. Most of the fatalities occurred in Lee County, Alabama, likely making that tornado the country's deadliest in nearly six years. Both the strength of the tornado and the types of homes in the storm's path are a stark reminder that advanced tornado warnings can only go so far in keeping people safe.

The Storm Prediction Center recorded 38 tornado reports as of 12:00 AM Central Time on Monday. Many of those tornado reports were likely duplicates from the same long-track tornadoes as they moved across Alabama and Georgia. The worst tornado moved through Lee County, Alabama, around 2:00 PM CST on Sunday afternoon. The tornado killed at least 23 people, with officials warning that the death toll could climb as rescuers comb through the debris.

It may not seem like it given the high death toll, but Sunday's tornado outbreak was a well-predicted and well-warned event. The SPC issued an enhanced risk for severe weather with its update on Saturday morning, giving residents a full day to prepare for the risk for dangerous thunderstorms.

Sunday began with an enhanced risk for tornadoes across the hardest-hit areas. The black hatching within that 10% risk zone indicated the risk for strong, long-lived tornadoes. The amount of wind shear and instability across the region was ideal for the development of supercells capable of producing strong tornadoes.

The SPC issued a tornado watch for the region at 11:40 AM CST, about two hours before the fatal tornadoes touched down. The storms were hauling toward the east at highway speeds, but meteorologists were able to keep up and issue alerts and warnings well ahead of their arrival.

The above radar image is enough to put a knot in your stomach when you know the environment is ripe for severe weather. If you're a frequent reader of my posts, you'll know that one of my go-to lines ahead of a severe weather day is "the severe threat will come in two rounds—first in discrete storms, then with the squall line that follows." Discrete storms are more likely to produce tornadoes and large hail, while the predominant threats with a squall line are damaging winds and occasional tornadoes.

Discrete thunderstorms are able to fully engage with the environment in which they develop. If they're far enough away from other storms, they can take advantage of all the instability and wind shear they need to attain the maximum strength the environment will allow. We saw that happen in abundance on Sunday. There were dozens of tornado warnings in effect at one point across the southeast, with many meteorologists remarking on Twitter that they can't remember how long it's been since we saw so many confirmed tornadoes occurring at once.

That discrete-before-the-squall scenario doesn't always materialize during a severe weather event. Oftentimes we'll see sloppy storm modes that result in widespread, blobby masses of thunderstorms that are rough, sure, but not what they could've been given the amount of wind shear and instability.

That's what happened up near Memphis during last week's severe weather threat. All of the ingredients were there...it's just that only a couple of storms were able to take advantage of it. (It turns out that the rare storm that could fully engage produced an EF-3 tornado in Columbus, Mississippi.)

A mesoscale discussion—basically a localized heads-up from the SPC—issued a full hour before the lethal tornado in Lee County, Alabama, actually pinpointed the affected areas as having the maximum risk for a strong tornado as the storms moved through. "Given the ample buoyancy and intense shear profile in place, it appears tornadogenesis will likely occur within the next 30-60 minutes with the possibility of a strong tornado occurring."

The NWS office in Birmingham issued a tornado warning for Lee County at 1:58 PM CST, continuing the warning polygon from the storm's previous track. The tornado was already on the ground by the time it entered Lee County's tornado warning. Radar imagery shows how quickly the storm wrapped up and produced an intense tornado. Forecasters soon upgraded the warning to a rare tornado emergency once it was clear that a destructive tornado was underway.

If you're familiar with radar imagery, you know this image. We've seen it too many times. This is a supercell like you'd see in a textbook. The tornado is the pendant at the end of the hook, right at the intersection of where the inflow of unstable air wraps in to meet the rear-flank downdraft pumping around the back of the system. The dark purple circle within the hook isn't just rain and hail—it's debris swirling around in the tornado. That's pieces of homes and trees and vehicles being picked up by the radar.

The long-track tornado appears to have followed the entire length of Lee County, continuing for a while across the Georgia border. The storm missed several dense population centers, including Auburn and Opelika to its north and Phenix City to its south.

Unfortunately, the storm missing population centers didn't keep the death toll down. A cursory look at satellite imagery along the tornado's path—confirmed by a scientist who study tornadoes in the southeast—shows that many of the homes damaged or destroyed in the storm were likely mobile homes. There are dozens of them on satellite imagery, some directly beneath the debris signature in the different radar images.

Meteorologists and other scientists are always working to lengthen the lead time ahead of a tornado. The longer ahead of time someone has a warning, the longer they have to get into a safe place and brace for impact. The SPC warned of the threat hours ahead of time and the NWS issued a tornado warning before the storm arrived. Local news channels showed the debris swirling around in the air on radar imagery as the tornado moved from town to town.

From beginning to end, this was a well-warned event.

We always focus on making sure as many people as possible hear a tornado warning the moment it's issued. But all of the advanced warning in the world can only go so far in preparing people for one of nature's strongest forces. Sunday's tornado was at least an EF-3 and probably stronger than that. The storm was moving at 60 MPH. Many of the residences in its path appear to have been mobile or modular homes. A human being simply cannot survive that kind of storm without being underground or deep within a much stronger structure. Many people in weaker homes out in the country simply have nowhere to go to ride out a storm like that. A tornado warning is only as good as your ability to act on it.

[Maps: me | Supercell Radar Images: Gibson Ridge]

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A Rare Tornado Touched Down Near Seattle on Tuesday

A strong tornado touched down in Port Orchard, Washington, on Tuesday, damaging several homes and businesses along its path. Meteorologists will conduct storm surveys on Wednesday to assign the tornado an EF-Scale rating, but pictures from local news organizations and social media seem to show that this was a formidable tornado in a part of the country that doesn't typically see this kind of weather.

Today's tornado in Port Orchard—which is next to Bremerton and about 30 miles west of Seattle—is a stark reminder that A) tornadoes can happen anywhere in the United States, and B) a significant number of tornadoes in the United States truly occur without warning.

The nasty weather today in the Pacific Northwest is directly tied to the same low-pressure system that generated all of the epic waves that hit the West Coast a couple of days ago. A long fetch across the northeastern Pacific Ocean allowed wave heights to reach 50 feet, posing significant risk to anyone ill-advised enough (to put it nicely) to go swimming or even just wander to the ocean's edge.

Each dot represents a lightning strike on December 18, 2018. Source: LightningMaps.org

Bursts of showers and thunderstorms moved across western Washington during the day on Tuesday, producing dozens of lightning strikes along the way. (That's nothing east of the Rockies, of course, but even one rumble of thunder out west is a talking point for days.) At least one of the thunderstorms was strong enough to tap into enough low-level wind shear to begin rotating.

The thunderstorm that produced today's tornado had a fairly pronounced signature on it as it crossed the Kitsap Peninsula. The storm's rotation grew strong enough to produce a short-lived tornado once it reached Port Orchard. Social media lit up as onlookers recorded a funnel that was mostly obscured by heavy rain but clearly present due to the immense amount of debris kicking up into the air. The thunderstorm quickly fell apart after the tornado touched down as more stable air wrapped in and choked off the instability feeding the storm.

We only had five-minute radar scans of the storms in northwestern Washington today—we're spoiled by rapid-scan radar imagery these days—but we did get a radar sweep at a critical moment: 1:51 PM PST, during or immediately after the tornado touched down and caused the most damage. That sweep took place at just the right moment to allow us to see debris in the air.

**BREAKING** New video showing a tornado near Port Orchard, WA, Tuesday afternoon just before 2. The @NWSSeattle is working to determine the extent of the damage and will have a storm survey team go out Wednesday morning. #wawx pic.twitter.com/2PRaaWqTCY

— WeatherNation (@WeatherNation) December 18, 2018

Dual polarization technology allows us to see the size and shape of the objects showing up on radar. Correlation coefficient (CC) tells us how similar or dissimilar airborne particles are to one another. Raindrops have a high CC value because they're all pretty much the same size and shape. Tornado debris, on the other hand, has a low CC because you're seeing everything from branches to vehicles being lofted into the air by the tornado.

Here's a two-pane radar image from Port Orchard around the time of the tornado. The left pane shows CC values while the right shows precipitation.

The debris on the CC imagery stands out as the dark blue circle near the center of the pane on the left. The radar beam is about 3,100 feet above ground level when it reaches the location of the tornado. Even if we didn't have videos of the tornado in progress, a quick look at that kind of a debris signature that high above the ground is a sign of a strong and sizable tornado.

It's common to see this somewhere like Alabama or Kansas, but not Washington. The Storm Prediction Center has more than 62,500 tornadoes in its database since reliable records began in 1950. Since then, only about 100 of those tornadoes occurred in Washington.

Heck, there are so few tornado tracks in Washington that you can barely make them out on a map of the whole country. You have to zoom in on the state to see them.

Most of the tornadoes reported in Washington over the past seven decades occurred along the coast, in valleys, and in the eastern part of the state where thunderstorms aren't as hampered by terrain and a stable marine layer as out west. The majority of Washington's tornadoes were relatively weak and short-lived.

The Storm Prediction Center's tornado database shows 121 tornadoes recorded in Washington between 1950 and 2017. More than half of those tornadoes—69 of them—were an F0 or EF-0 on the Fujita and Enhanced Fujita scales. (The Fujita scale was updated as the Enhanced Fujita Scale in 2007.) Only three tornadoes in Washington have produced F3/EF-3 damage. Based on pictures of the damage, today's tornado is likely to get at least an EF-1 rating, if not higher.

Tornadoes are rare in Washington, and strong tornadoes are even rarer yet. They're so rare, in fact, that the National Weather Service office in Seattle hasn't issued a tornado warning in more than four years—including today. Residents of Port Orchard had no tornado warning or severe thunderstorm warning before the tornado touched down. They only knew there was a tornado if it hit them, they saw it, or they heard about it afterwards.

For all the talk of false alarms when it comes to tornado warnings, an uncomfortable fact we have to live with is that quite a few tornadoes actually wind up going unwarned. The National Weather Service fails to issue a tornado warning for 30-50% of all tornadoes that form each year. The agency does better warning for tornadoes that occur during organized outbreaks than in one-off situations like we saw today.

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The Anatomy of the April 15, 2018 Tornado in Greensboro, N.C.

One of the strongest and longest-track tornadoes to hit North Carolina's Piedmont Triad in years touched down on the evening of Sunday, April 15, 2018. The EF-2 tornado developed just east of downtown Greensboro shortly after 5:00 PM on Sunday and tracked north along a 33-mile path before dissipating south of Danville, Virginia. The tornado damaged more than 1,000 buildings in Guilford County, North Carolina, alone, and resulted in one indirect fatality and at least 14 injuries. The thunderstorm responsible for the tornado left behind a path of wind and tornado damage from central South Carolina through central Virginia.

The Setup

April 15 was the third day of severe weather in an outbreak that began on the Plains on the evening of Friday, April 13. The storms that formed over the two previous days resulted in at least one fatality in Louisiana and injured a dozen more people as strong winds and tornadoes caused a swath of damage focused on Louisiana, Arkansas, and Mississippi.

The system responsible for the previous severe weather continued into the Ohio Valley on the morning of Sunday, April 15. Strong southerly winds near the surface raised temperatures and dew points into the 60s and 70s across the southeast during the day on Sunday, helping to provide enough instability to fuel severe thunderstorms. Winds from the southwest in the middle- and upper-levels of the atmosphere provided the wind shear necessary to organize the thunderstorms into squall lines and allowed some storms to rotate and produce tornadoes.

The Storm Prediction Center issued a risk for severe thunderstorms across the southeast and Mid-Atlantic during the day on Sunday. The threat stretched from the foothills of eastern Ohio south through the Florida Peninsula. An enhanced risk for severe weather existed across portions of the Carolinas and south-central Virginia due to the elevated risk for tornadoes.

Forecasters noted that there was a 10% risk for tornadoes across an area stretching roughly from Savannah, Georgia, north through Martinsville, Virginia, in response to strong wind shear that could allow thunderstorms in or ahead of the squall lines to begin rotating. This was only the seventh time in the past ten years that the immediate Greensboro area found itself under a 10% or greater tornado risk in a SPC forecast.

The Thunderstorm

Most of the storms that formed on April 15 were part of squall lines moving west to east across the southeast. You can trace the individual thunderstorm that produced the Greensboro tornado from its formation around 10:30 AM in southern Georgia all the way until it produced another destructive tornado near Lynchburg, Virginia, almost eight hours later. 

This thunderstorm was the most persistent and destructive out of all the individual cells that formed in the southeast on April 15. The storm began as part of a squall line in southern Georgia around 10:30 AM, quickly strengthening as it moved toward Columbia, South Carolina. The airport in Columbia reported a 74 MPH wind gust as the storm moved through. 

The National Weather Service in central South Carolina confirmed four tornadoes west of Columbia as the storm moved through: one EF-2, two EF-1s, and one EF-0. These tornadoes all had a path length of 3 miles or less, which is common for storms that form as part of a squall line. The tornadoes occurred between 2:00 PM and 3:00 PM.

It appears that the storm gradually acquired characteristics of a supercell as it moved into North Carolina. It developed a sustained mesocyclone (rotating updraft) as it moved east of Charlotte and toward Asheboro. The storm in question eventually separated from its main squall line as it moved along Interstate 74 between Asheboro and Greensboro. 

The storm separating from the squall line appears to have allowed it to fully engage with the favorable environment it encountered—sufficient instability and strong wind shear—to produce the tornado near Greensboro. The rotation weakened as the storm once again merged into the squall line from which it came, and the storm regained its rotation when the storm yet again broke away from its parent squall line as it approached Lynchburg.

The Guilford-Rockingham Tornado

The tornado touched down just north of Interstate 40 on the eastern side of Greensboro, North Carolina, at 5:07 PM. The tornado damaged multiple homes and Peeler Elementary School as it strengthened and moved north.

Hampton Elementary School took a direct hit from the tornado as it reached its peak intensity with 135 MPH winds at 5:10 PM, producing damage that was right on the border between EF-2 and EF-3 intensity on the Enhanced Fujita Scale. Meteorologists from the National Weather Service in Raleigh estimated the tornado's peak intensity by the complete destruction of mobile classrooms at the elementary school.

Television station WFMY had to delay their live coverage of the tornado as their crew and staff sought shelter in a hallway while the tornado tore up neighborhoods not far from the station.

A tree fell on a car near the intersection of E. Cone Blvd. and Cesar St. in Greensboro. The driver passed away from his injuries. This was the only fatality caused by the storm, but it was far enough away from the tornado's track that it appears strong thunderstorm winds took down the tree rather than the tornado itself.

The tornado continued damaging hundreds of homes as it moved north away from the school and out of Greensboro city limits into unincorporated Guilford County. The path of damage shows the tornado slowly changed course toward the northeast until the storm eventually paralleled U.S. Highway 29.

Guilford County Emergency Services estimates that more than 1,000 structures were damaged by the storm in Guilford County alone; 199 homes and businesses suffered major damage (162) or were completely destroyed (37).

Raleigh's storm survey estimates that the tornado was an EF-0 with 80 MPH winds when it crossed into Rockingham County at 5:24 PM.

A significant amount of debris fell on southern Reidsville (where I live) as the tornado weakened and passed a few miles to the southeast of the city around 5:30 PM.

I witnessed several pieces of plywood and insulation fall from the sky before the winds picked up. I took a walk around my apartment complex after the storm and found a significant amount of insulation, large shards of plywood from buildings, many shingles, several large pieces of metal, a computer cable, a window screen, a six-foot strip of vinyl siding, and some other structural debris that fell during the storm. Several large pieces of sheet metal, presumably used as roofing material, also managed to make it up to Reidsville.

It's common to hear of light objects like papers or photographs traveling many dozens of miles after a strong tornado, but the amount of debris that fell on Reidsville surprised me. Most of the debris was able to make it the 15+ miles from Greensboro to Reidsville because it was light enough to easily float in the wind or its surface area was great enough that the debris caught the wind like a sail. Some of the pieces of metal were easily 10 or 20 pounds—so heavy that I couldn't throw them 10 feet let alone the 15 miles they were carried by the tornado—which is a testament to the power of both the tornado and its parent thunderstorm.

It appears that the reason so much debris from Greensboro fell on Reidsville is that the storm weakened as it approached Rockingham County and the tornado itself changed direction even as the winds in the lower- to mid-levels of the atmosphere stayed the same. Doppler radar data shows debris lofted nearly 20,000 feet into the atmosphere as it moved through eastern Greensboro. The radar data shows the debris moving with the thunderstorm over the next 20 minutes as it slowly descends before the bulk of the debris falls out over southern Reidsville.

A couple of minutes later, the tornado restrengthened and reached EF-2 intensity with winds of 125 MPH as it destroyed a mobile home and damaged multiple homes along Grooms Road in eastern Reidsville. The mobile home tumbled several hundred feet across the road, striking a moving vehicle and critically injuring the driver and his son.

The tornado continued through Ruffin, North Carolina, before finally dissipating at 5:46 PM.

Two more tornadoes would occur along the path of this storm for a total of seven during the thunderstorm's lifespan. The storm produced another tornado in the City of Danville shortly after the storm crossed into Virginia, leaving behind EF-1 damage along its 12-mile path. A little more than an hour later, the same storm produced an EF-3 tornado near Lynchburg, Virginia, destroying many homes and injuring at least 12 people along a 20-mile track.

The initial tornado warning for this storm was not issued by NWS Raleigh until 5:09 PM, two minutes after the tornado touched down. The warning was amended at 5:16 PM to indicate that a tornado was confirmed due to the presence of debris on radar. NWS Blacksburg issued a tornado warning for Rockingham County at 5:18 PM, six minutes before the tornado crossed the county line and 15 minutes before it injured people in Reidsville.

You can read the storm surveys conducted in Guilford County and Rockingham County, as well as the text of the tornado warnings for both Guilford and Rockingham Counties.

Triad Tornadoes

Significant tornadoes aren't common in the Piedmont Triad, which encompasses Greensboro, Winston-Salem, Burlington, and surrounding communities. Tornadoes that do form in the Triad are typically weak and short-lived. Before last week, only five tornadoes in the past 20 years to form in this area were rated F2/EF-2 or higher on the Fujita Scale.

Tornadoes are most common in the eastern part of North Carolina where the ingredients for outbreaks are more often present due to the flatter terrain and more favorable environment closer to the ocean. The presence of stable air and influence of the mountains typically reduces (but by no means eliminates) the tornado threat in central and western North Carolina.

Not only was the tornado uncommonly strong for its location, but the Guilford-Rockingham tornado remained on the ground for 33.6 miles—a rare feat for tornadoes in North Carolina. The National Weather Service recorded 1,255 tornadoes in North Carolina between 1950 and 2016. The average path length for tornadoes in North Carolina is just 3.55 miles. Only 18 of those 1,255 tornadoes (1.4%) had a path length of 30 miles or longer, and the vast majority of those long-tracked tornadoes occurred in the eastern part of the state. Sunday's tornado was the 19th such storm.

[Maps and Images by Dennis Mersereau | Radar: Gibson Ridge]

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