March 24, 2020

Some Strong Tornadoes Are Possible In Alabama And Tennessee On Tuesday Evening

Not for nothing, but the recent questions about whether it's safe to break social distancing to seek shelter from tornadoes in community storm shelters wasn't a hypothetical. There's a risk for severe thunderstorms across parts of the southeastern United States this afternoon and evening, with a risk for damaging winds, large hail, and tornadoes. Some of the tornadoes could be strong or long-tracked. The threat will ramp up in the late afternoon and evening hours, clearing out as the night progresses.

Today's setup is common for what you'd see on a late March afternoon. A weak low over southeastern Oklahoma will set the stage for the severe weather today. Thunderstorms will develop in the warm, muggy air over the southeastern states as the low moves east through the evening.

Severe thunderstorms are possible this afternoon and evening across a wide area from Little Rock to Myrtle Beach. Any thunderstorms that form across this area today could produce damaging wind gusts in excess of 60 MPH, hail the size of quarters or larger, and tornadoes.

There's plenty of wind shear in the atmosphere for thunderstorms to organize into supercells along and near the warm front. As a result, the Storm Prediction Center issued an enhanced risk for severe weather in northern Alabama and southern Tennessee, including Huntsville, Decatur, and Florence. The area under the enhanced risk got upgraded due to a 10% risk for "significant" tornadoes, which means the environment is capable of supporting strong (EF-2+) or long-tracked tornadoes.

Most folks are home right now as a result of school and business closures. It's important to pay attention to the weather even as we try to distract ourselves from the boredom at home. Peeking at the radar on a weather app, leaving local news or The Weather Channel on in the background, keeping the NWS open in another tab...anything that keeps the weather in constant view is a good plan today so warnings don't pop up by surprise.

The best way to receive tornado warnings is to activate the emergency alerts on your smartphone. Even if all the other alerts are disables, make sure tornado warnings are switched on. These alerts go off the moment a tornado warning is issued for your location. They've alerted me to tornado warnings when I wasn't paying attention before, and I'm constantly staring at the radar. It's a good system to have.

Oh, one more thing. Please...pretty please...don't rely on tornado sirens for tornado warnings. These systems are only designed to be heard outdoors and there's no guarantee they'll work at all in the middle of a raging thunderstorm.

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March 23, 2020

Storm Shelters: It's OK To Skip Social Distancing For An Hour If It Means Surviving A Tornado

Most Americans are parked at home right now as we try to slow the spread of a dangerous virus that's moving through communities here and around the world. But even as we adjust our lives to spare one another, the world continues around us just as it ever would. We're quickly moving into the heart of severe weather season and it won't be long before we have to deal with tornado outbreaks on top of everything else that's going on. It's important to remember that sheltering from a tornado is an urgent matter of life or death that (at least, temporarily) overrides our need to practice social distancing.

This may seem like a weird question to ponder for folks who live outside of the southern United States, but it's a pressing concern for lots of people who don't have safe shelter at home.

The concept of "community storm shelters" has grown in popularity in the south, especially after several devastating tornadoes and tornado outbreaks during the 2010s. A community storm shelter is a large reinforced room designed to hold lots of people—sometimes an entire neighborhood—who don't have a better alternative to ride out a storm.

Now that we're trying to slow the spread of COVID-19, huddling together with a few dozen of our neighbors doesn't sound like the best thing to do right now. The rapid approach of severe weather season is going to force people to choose between social distancing and staying safe from a tornado. Seeking shelter from a tornado is absolutely the best bet. In a dangerous situation like this, it's absolutely riskier to stay in an unsafe home and hope the tornado misses than it is to come in close contact with your neighbors.

The Alabama Department of Public Health released a joint statement with the National Weather Service offices in Huntsville, Birmingham, and Mobile, on Sunday addressing this concern. Their advice is simple: the urgent risk posed by a tornado temporarily outweighs the risk of the virus, and to seek shelter if one is available.

As the statement points out, it's critically important to know whether or not a shelter is open before severe weather strikes. If not, make alternate plans to stay somewhere safe before a warning is issued.

Tornado safety advice tells us to seek shelter in an interior room on the lowest level of a home or building. The goal is to put as much distance between you and the wind and flying debris as possible. The aftermath of stronger tornadoes often leaves just an interior bathroom or closet standing even as the rest of the house is swept away.

That's not always an option for some communities. Millions of people live in mobile homes that can barely withstand the wind gusts of a potent thunderstorm, let alone the violent winds of a tornado. Millions more live in homes without basements, modular homes, or apartment buildings, all structures in which you're often reduced to picking the least-worst option to ride out a tornado.

Folks who live in homes that can't withstand strong winds have to go somewhere else to stay safe ahead of a tornado. It's common practice for folks who live in mobile homes, for instance, to spend the day at the library or at a friend's or relative's house on a severe weather day. Unfortunately, there aren't many public spaces left open to seek shelter—libraries, schools, restaurants, and most other businesses are closed, which can limit one's options in a pinch.

Do what you need to do to stay safe. But during a tornado, it should go without saying that you've got to get to a safe place to ride out the storm.

Weather safety advice has come a long way in the last couple of decades, but there are still some pressing questions for which there's no easy answer. The most analogous scenario to this "distance or shelter?" question was a situation faced by thousands in and around Houston during Hurricane Harvey in 2017. The storm produced historic flooding in southeastern Texas, and, as we commonly see during a landfalling tropical system, many of those heavy thunderstorms wound up spawning tornadoes. This put lots of people in the horrible situation of choosing between staying low in the water to escape the tornado or climb high away from the water and hope the tornado missed.

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March 19, 2020

A Widespread Threat For Severe Weather Will Cover The Central U.S. On Thursday Evening

A widespread risk for severe weather will develop across much of the central United States on Tuesday as warm, humid air surges northward behind a warm front. Several rounds of severe thunderstorms will develop through Thursday night, bringing the risk for damaging winds, tornadoes, and large hail. The greatest tornado risk appears centered on the Mississippi and Ohio Rivers.

Today's severe weather threat looks like the first large-scale severe weather threat of the season, with a slight risk extending from Waco to Milwaukee, Grand Island to Columbus, and everywhere in between. The Storm Prediction Center issued two separate enhanced risk areas for Thursday evening; one covers the threat near the center of the low-pressure system across portions of Iowa, Missouri, and Nebraska, while the other covers the threat for severe storms between central Arkansas and southern Indiana.

Source: Tropical Tidbits

You can see the basic setup by glancing at a map of dew points this afternoon. There's a beautiful low-pressure system centered right over the Colorado/Kansas border this afternoon—look at the moisture swirling around its center!—with a series of warm fronts extending from there all the way east to the Delmarva Peninsula. This swath of warm and humid air will fuel the development of thunderstorms this afternoon and evening, and strong wind shear through the atmosphere will allow many of the storms to grow severe. The warm front will serve as a focus for the tornado threat across Iowa, Missouri, and Nebraska, while a low-level jet will drive this evening's tornado risk in the Mid-South and Ohio Valley.

A 10% risk for tornadoes exists across both of the enhanced risk zones, with slightly lower threats radiating out from there. That doesn't sound like much, of course, but when you consider there's typically about a 0.1% to 0.2% risk for a tornado within 25 miles of any location across today's risk areas on an average March 19, today's 10% risk should make everyone's ears perk up and pay attention to the radar.

Damaging winds are likely in any of the thunderstorms that form today. Don't sleep on the damage that can result from 60+ MPH wind gusts. It's important to take severe thunderstorm warnings seriously, as well. Flowers and leaves are developing on the trees now, which can act like little sails by catching the wind and adding stress to limbs and trunks.

Any of today's severe thunderstorms could produce large hail (the size of quarters or larger), but there's a risk for "significant" large hail—the size of golf balls or larger—across the enhanced risk in IA/MO/NE.

Nighttime tornadoes are exceptionally dangerous because people are tuned-out, asleep, or they can't fight their urge to look outside and visualize the threat before they take action. As always, make sure wireless emergency alerts are activated on your phone before you tune-out or go to bed tonight. Given the advanced radar technology available to meteorologists today, you can trust that you're at risk if your location goes under a warning.

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March 12, 2020

There's A Risk For Some Strong Tornadoes Over The Western Ohio Valley On Thursday

Severe thunderstorms are likely across parts of the Ohio Valley and Mid-South on Thursday afternoon. Some of the thunderstorms will be capable of producing tornadoes, some of which could be strong or long-tracked. 

The Storm Prediction Center issued an enhanced risk for severe weather from southeastern Missouri to central Kentucky, with slight and enhanced risks radiating out from there to cover a wide area from northern Texas to central North Carolina. The bullseye for severe weather is the western Ohio Valley, including Bowling Green and Evansville. This is the area where conditions are most favorable for supercell thunderstorms capable of producing tornadoes.

A low-pressure system developing over the mid-Mississippi Valley on Thursday morning will provide the focus for strong to severe thunderstorms to develop across the risk area. There’s enough lift and wind shear for thunderstorms to develop into supercells capable of producing tornadoes. Conditions appear favorable enough across the enhanced risk area that some of the tornadoes could be “significant,” per the SPC, which means that the tornadoes could be strong or long-tracked. This is most likely along or near the warm front, since surface boundaries tend to serve as a focal point for tornadoes.

If you’re in or anywhere near the areas that could see severe thunderstorms today, the best way to prepare is to make sure that the emergency alerts are activated on your phone. It’s the best way to receive tornado warnings the moment they’re issued for your location. Emergency alerts are located prominently in your phone’s settings. Folks tend to disable all of the alerts after one ill-timed disruption for a flash flood or AMBER Alert; leaving these alerts enabled for tornado warnings is a good idea no matter how many disruptions they cause.

Source: NWS Nashville

The region is still reeling from last week’s severe weather. Several destructive tornadoes moved across central Tennessee early in the morning on March 3, producing severe damage up to EF-4 intensity across a path dozens of miles long. One of the tornadoes moved through the northern part of downtown Nashville, the second intense tornado to strike the city center in the last 22 years. (An F3 hit the downtown core in 1998.)

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March 3, 2020

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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