June 17, 2024

Extreme heat kills. It's no joke. Folks shouldn't treat it like one.

If a tornado outbreak killed a few hundred people, it would be remembered as a national tragedy. 

When a heat wave kills a few hundred people, it's the butt of countless jokes. 

People are wimps. Just turn on a fan.

Get used to it like we are down here. It's just called summer.

That kind of nonsense shows up every time there's a prolonged extreme heat event and it's never any less enraging.

Extreme heat is one of the deadliest weather events in the world.

It's not a made-for-television disaster, but it's there whether we see it or not—silently claiming parents and grandparents, striking down perfectly healthy kids at football games, exacting a horrible toll on lower income people already struggling to make ends meet.

Heat waves are responsible for nearly half of all disaster-related fatalities. Heat has claimed an average of 188 lives per year over the past decade, compared to 103 flood-related deaths and 48 tornado-related fatalities over the same period.

Hot temperatures are relative. A 90°F day with humidity requires a level of acclimatization to handle. Someone living in Orlando, Florida, will have an easier time slogging through a scorching day than someone up in Burlington, Vermont. But not even everyone in the south has access to air conditioning. Extreme heat still kills and injures vulnerable people in the humid southeast and the deserts of the southwest.

It's not just a matter of what you're used to.

Lots of homes in the northern United States and throughout Canada still don't have air conditioning—whether by design or simply for lack of affordability. These homes become unbearably hot when the outside temperature climbs above just 80°F. Throw higher readings and some heat-retaining humidity into the mix and you have a recipe for extreme physical stress just trying to exist.

Heat waves also compound on themselves. Humid heat doesn't allow for any relief at night. Hot days spilling into hot nights wrap around you like a wet blanket when you don't have air conditioning to stay cool. Fans don't help in that kind of setup.

You're left with a situation where hundreds of thousands of vulnerable neighbors, friends, and family members are left to their own devices, hoping they see relief at the end of a days-long nightmare. They're lucky if they can get to a cooling center or visit someone for some relief from the stifling air. Many of them are forced to grin and bear the suffering, hoping that they're able to stay hydrated enough to stave off heat exhaustion or heat stroke.

Extreme heat is no joke.

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June 16, 2024

Tropical disturbance, unusually hot ocean likely to fuel Gulf Coast flooding this week

A tropical disturbance slowly moving into the western Gulf of Mexico will bring copious amounts of rain over the next couple of days, leading to a threat for flash flooding across coastal portions of Texas and Louisiana.

Forecasters expect the heaviest precipitation to fall over coastal Texas, where 5-10 inches of rain is possible through the middle of the week. Locally higher totals are possible. The region has famously poor drainage—especially the Houston metro area—so the likelihood of flash flooding during heavy rain is almost a given.

Remember, never try to drive across a flooded roadway. It's impossible to tell how deep the water is until it's too late, and the road may be washed out beneath the floodwaters. It only takes a few inches of moving water to lift up a vehicle and carry it downstream.

The slug of moisture is arriving with a tropical disturbance moseying into the western Gulf of Mexico. The National Hurricane Center gives the area a 60 percent chance of developing into a tropical depression over the next few days as it moves into the region.

Heavy rain is coming whether or not this develops into a named system. Some of the worst heavy rain events are the result of unnamed tropical disturbances—just look at what happened in Florida last week.

A tropical disturbance sent a vast amount of tropical moisture streaming over southern Florida. Persistent thunderstorms developed over the region, wringing out that moisture in the form of drenching rains that fell at several inches per hour at times.

Some areas wound up with more than two feet of rain, with the National Weather Service's latest precipitation analysis showing even more than that over the past ten days.

This latest tropical disturbance is a reminder that the Atlantic Ocean is open for business—and this season could mean business.

All major hurricane forecasts are calling for an extremely active hurricane season with predictions rivalling the busiest seasons on record. We could see more than 20 named storms this year if the forecasts pan out.

Extremely warm sea surface temperatures are driving those forecasts—and they're also likely driving the persistent heavy rain we've seen (and will soon see) across the Gulf Coast.

Warmer waters raise air temperatures over the ocean, allowing the air to hold more moisture than it would otherwise. It's likely that warmer sea surface temperatures are increasing the amount of moisture we're seeing over the region, which is enhancing rainfall totals in turn.

How unusually warm is the ocean right now?

Sea surface temperature anomalies are running 1-2°C above normal throughout almost the entire tropical Atlantic basin. 

Compare that to this time last year, where the extent and intensity of anomalies were still ugly, but a little less intense than we're dealing with this year:

It's worth noting that last year's very warm temperatures were able to fuel one of the most active hurricane seasons on record, overpowering the influence of El Niño which tends to subdue tropical activity in the Atlantic. 

This year, though, we've got even warmer waters and a La Niña in the Pacific, which is favorable to tropical development in the Atlantic. It could be a long, rainy summer. Hold on.

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June 12, 2024

High-impact heat set to build over much of the U.S. through mid-June

The jet stream is moving to Canada—and you might also want to head north after seeing the temperatures on the way over the next week or longer.

A long-duration spell of warmer-than-normal temperatures will bathe the eastern half of the United States through the middle of the month as a ridge takes hold over the region.

Not only will this pattern crank up the heat, but it may finally shut off the Ferris wheel of severe thunderstorm outbreaks we've endured since early spring.

The Temperatures

It's already plenty hot across the Plains and the southeastern corner of the country, where temperatures on Wednesday easily climbed into the 90s for many locations.

We'll see that heat spread north and east as the ridge builds into place through the weekend, with daytime highs pushing into the upper 80s and lower to mid-90s by Sunday.

The warmth isn't going anywhere in a hurry, with highs in the 90s likely across the eastern seaboard all through next week and possibly into the following weekend.

Here's a look at the National Weather Service's forecast high temperatures on Monday, June 17...

...and here's a look at Tuesday's predicted high temperatures:

The Setup

A jet stream parked over the northern tier of the United States has driven the drumbeat of severe weather over the past couple of months. One low-pressure system after another cresting the Rockies and roaring through the central U.S. has fueled a healthy thunderstorm season.

We just experienced our second-most tornadic April on record, and the Storm Prediction Center announced Tuesday that last month was one of the most severe Mays on record.

Image: Tropical Tidbits

The jet stream tends to migrate north as summer settles in, which helps push severe weather farther to the north—while also letting the heat build to the south.

Models are consistently showing ridges of high pressure parked over the eastern half of the United States through the middle of the month. Air sinks beneath ridges, warming up as it descends toward the ground.

A persistent ridging pattern will keep temperatures much warmer than normal for a week or longer, which is no small thing considering average temperatures in the latter half of June are pretty warm to begin with.

Heat Impacts

This is the first large-scale test of the National Weather Service's new HeatRisk product, which measures the potential impact of high heat on certain regions. HeatRisk takes into consideration factors like:
  • The time of year
  • How far above normal temperatures are for that time of year
  • How long the unusual heat will stick around
  • Temperatures reaching thresholds known to cause heat-related illnesses
Urban areas are regions farther to the north are likely to experience higher risk from heat than communities down south. Access to cooling and your body's physical acclimation to heat plays a significant role in heat impacts. A 90°F and humid day is far different for folks living in Mobile, Alabama, than it is for a lifelong resident of Detroit, Michigan.

The potential for major to extreme heat impacts light up the board across the central and northern U.S. over the next week given the latest NWS temperature forecasts. The greatest risk focuses on the Midwest by the end of the weekend, pushing toward the Great Lakes by the beginning of next week.

The compounding effects of hot, humid days and stuffy, muggy nights will take a toll on vulnerable people—especially those without reliable access to air conditioning. Take care if hot temperatures are on the way to your area. It's easier to succumb to heat exhaustion or worse than you think, even for someone who's otherwise healthy.

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June 9, 2024

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.


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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June 4, 2024

Extreme heat builds across the western U.S. this week

The atmosphere looked at the calendar this week and decided to turn up the heat.

We're at the beginning of a multi-day stretch of dangerously hot temperatures across the interior West, with temperatures in the triple digits expected for the deserts and California's Central Valley.

Excessive heat warnings are in effect for much of the region.


Image: Tropical Tidbits

A powerful ridge of high pressure building over the western U.S. is responsible for the impressive heat we'll see over the next few days. Air warms up and dries out as it sinks beneath an upper-level ridge, keeping temperatures much hotter than normal beneath the blazing sunshine.

That ridge will put in work this week as temperatures soar from Oregon to Texas.

The National Weather Service has issued excessive heat warnings and heat advisories for much of the region to warn folks of the hazards they'll face through the end of the week.

Daytime highs will climb over 100°F in Sacramento, Las Vegas, and Phoenix on Tuesday, with the worst heat arriving on Wednesday and Thursday.

This is the first widespread test of the NWS's new HeatRisk product, which offers guidance on the impacts of extreme heat across the country.

We'll see major to extreme impacts for many communities affected by the hot temperatures over the next couple of days, with the most widespread impacts likely during the day Wednesday.

Even though nighttime lows will provide some relief from the extreme daytime heat, this is going to be a dangerous spell of hot temperatures for vulnerable people. Fans alone won't be adequate to cool indoor spaces. People will need air conditioning to avoid heat-related illnesses, which can set in quickly when temperatures rise into the 100s.

Extreme heat affects people who are otherwise healthy. It's very easy to get dehydrated in extreme heat, especially out west where humidity is often quite low during major heat events. Sweat evaporates more efficiently when it's dry outside—too dry and too hot and you'll quite literally sweat yourself into dehydration, which can quickly lead to heat exhaustion or heat stroke.

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May 24, 2024

Rinse and repeat: yet another wave of dangerous storms expected Saturday

One active pattern after another sweeping across the U.S. this season will just keep on going as we head into the start of the Memorial Day weekend.

The Storm Prediction Center (SPC) issued a moderate risk, a level 4 out of 5, for much of Oklahoma and Kansas on Saturday as widespread severe thunderstorms are expected to develop across the region.

"Strong to violent tornadoes" are possible, the SPC said in its forecast on Friday afternoon.

The Setup

Fresh on the heels of a low-pressure system that generated powerful tornadoes comes...yet another low-pressure system that could generate powerful tornadoes.

Forecasters expect a low to quickly develop and strengthen over the central Plains during the day Saturday.

Image: Twister Data

Ample heat and humidity over the southern Plains, combined with lift provided by the approaching low and strong wind shear aloft, will set the stage for widespread severe thunderstorms from northern Texas through southern Nebraska.

The model graphic above from TwisterData.com is valid for about 7:00 p.m. CDT on Saturday, showing the Energy Helicity Index (EHI).

EHI is a parameter that takes into account both instability and wind shear. Values above 2.00 are sufficient for supercells, with higher values indicating a more favorable environment for supercells that could produce tornadoes. It's not hard to see how favorable the setup is for tornadic and hail-producing supercells on Saturday afternoon and evening across the areas highlighted by the SPC.

The worst of the weather is expected across much of Oklahoma, Kansas, and far western Missouri. This includes Oklahoma City, Tulsa, Wichita, and Kansas City.

The Risk

The SPC's moderate risk is in effect due to the potential for all modes of significant severe weather across the region. 

TORNADOES: A growing risk for intense and long-lived tornadoes will exist within any discrete supercell thunderstorms that form away from other clusters of storms. These supercells could also produce very large hail the size of golf balls or larger.

WINDS: As the evening wears on, and as we so often see, those individual thunderstorms will begin to merge into one or more squall lines that races east through the overnight hours. These lines will carry a risk for widespread damaging winds with gusts of 75+ mph possible. There is a risk for fast-moving embedded tornadoes within these squall lines. Damaging winds are a particular risk through areas like Tulsa, Wichita, and Kansas City.

TIMING: Thunderstorms will begin to bubble through the western half of the risk area during the day on Saturday. The greatest risk will evolve through the early evening hours, continuing into Saturday night and the wee morning hours Sunday.  

Safety Tips

Be proactive. Don't let storms take you by surprise. Keep an eye on the radar and local news for live storm coverage, and stay aware of storms heading in your direction.

Make sure you have a way to receive severe weather warnings the moment they're issued. Take a look at your phone and ensure emergency alerts are turned on for tornado warnings. These free push alerts are proven lifesavers, and they only warn you if your location is included in the warning so you know it's nothing to ignore. 

Do not rely on tornado sirens as your first line of defense. Tornado sirens are not meant to be heard indoors. These systems are unreliable and prone to failure.

Form a plan in advance for where you'll seek shelter if you're under a tornado warning. Stay on the lowest level of the building in an interior room, putting as many floors and walls between you and flying debris as possible. Keep blankets, pillows, and a bicycle helmet handy to wear while sheltering. 

Manufactured and mobile homes offer no protection from even the weakest tornado. If you're in one of these unsafe structures, have a secondary shelter location in mind and go there before the storms arrive.

Wear closed-toe shoes today to protect your feet if you have to walk through debris.

If you're driving when a tornado warning is issued, do not stop under an overpass. Bridges offer no protection from tornadic winds or flying debris—they actually make the winds stronger. Stopping under a bridge to shelter from a tornado or large hail often causes traffic jams that can lead to serious car accidents or worse if a tornado hits that location.

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