Second Tornado Outbreak Expected On The Plains Saturday

All signs point to a second tornado outbreak developing across the southern and central Plains on Saturday as a multi-day severe weather event unfolds over the region.

A moderate risk for severe weather—a 4 out of 5 on the scale measuring the threat for severe thunderstorms—is in place for much of Oklahoma and portions of northern Texas and southeastern Kansas. 

Multiple violent, long-lived tornadoes are possible from Texas north toward Iowa, including major cities like Dallas, Oklahoma City, Wichita, Kansas City, and Omaha. Severe storms will also be capable of producing hail larger than golf balls and destructive wind gusts of 75+ mph.

Storms were already developing on the western edge of the risk areas as of this post's publication around 11:30 a.m. CDT. We'll see thunderstorms increase in coverage and intensity through the afternoon, with the greatest threat pushing into the moderate risk area through the late-afternoon and early evening hours. 

Saturday's severe weather follows a horrible tornado outbreak that struck the central Plains on Friday, including more than a dozen confirmed tornadoes. The worst storms hit Nebraska, where multiple violent and long-track tornadoes tore through communities in the central and eastern portions of the state.

One of the tornadoes near Lincoln, Nebraska, was caught on a traffic camera on I-80 as the storm roared across the highway. Forecasters will survey the damage once conditions settle down, and it's likely that a few of the twisters will receive high-end ratings on the Enhanced Fujita Scale.

The big news from Friday's storms, though, is the fact that there were apparently zero fatalities amid all the damage. It's a miracle of modern science and warning technology that multiple intense twisters levelled neighborhoods and—at least as of now—nobody died. 

Friday's warning success story is a testament to the power of tornado warnings and good weather communications. A more widespread outbreak on Saturday makes it even more important to ensure you have a way to receive severe weather warnings the moment they're issued.

Ensure emergency alerts are activated on your phone for tornado warnings. These free push alerts pop up on your phone the moment your location is placed within a tornado warning. The alerts are geotargeted to only alert you if you're in the warning polygon—you'll only get it if you're in danger.

It's important to have multiple ways to receive alerts in case one method gets delayed or outright fails. Keep tabs on the radar so you know what's coming in advance.

Take a look at the weather apps on your phone and make sure they're set to deliver tornado warnings for your current location. Local television news will run wall-to-wall coverage when tornado warnings are in effect. Most stations run livestreams online if you don't have cable or antenna. 

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NWS Unveils New 'HeatRisk' Forecasts to Highlight Dangers of Extreme Heat

Heat kills more Americans every year than tornadoes, hurricanes, lightning, and flash floods combined. A new product released by the National Weather Service aims to cut down the tremendous number of heat-related illnesses and fatalities we see across the country every year.

HeatRisk is the culmination of a joint effort by the NWS and health experts with the Centers for Disease Control to increase awareness of the dangers of extreme heat throughout the U.S.

The new product is similar to the Winter Storm Severity Index in that it uses a five-category scale to relay the dangers posed by conditions on a particular day.

According to the NWS, forecasters will consider 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

Those are important considerations when it comes to heat safety. A heat wave in May might warrant a higher rating as it may deliver a greater "shock to the system" (so to speak) than similar heat in August. Time, place, and duration all play a major role as well. A week of 90°F readings in Florida might not affect residents as much as a week of 90°F readings in Vermont.

HeatRisk will show up in products and on maps using a five-category scale ranging from 0 to 4, with "little to no risk" on the low end to "extreme impacts" on the high end. These categories are designed to quickly convey the severity of heat in the forecast for any particular area.

If you're in the red for "major impacts," for instance, it's going to be hot enough that fans won't effectively cool down indoor spaces, and anyone outdoors in the heat of the day—even healthy individuals—are at risk for heat-related illnesses.

Why this standardized scale matters

Excessive heat is a silent killer. A widespread heat wave can kill dozens and even hundreds of people without ever making the news. Elderly people, folks living with chronic conditions, and people working and living outdoors routinely succumb to heat exhaustion and life-threatening illnesses like heat stroke.

We're bombarded by alerts for tornadoes, hailstorms, hurricanes, and even wildfires. But heat—a deadlier threat than them all—routinely gets shrugged off. It's just summer, after all, what's the big deal?

This kind of a product is a long time coming. For years, we've relied on the heat index and the wet bulb globe temperature (WBGT) to measure the impacts of heat on the human body.

Meteorologists and medical scientists worked together to create the heat index to measure the combined impact of temperature and humidity on the human body. The NWS uses the heat index as a metric to issue heat advisories and excessive heat warnings, the thresholds for which are higher in areas like Phoenix or Miami than they are in cooler climates like Boston or Seattle. 

The wet bulb globe temperature (WBGT) goes a step further by factoring in more than just the temperature and humidity, including parameters like cloud cover, winds, and the sun angle to more accurately judge heat stress on the human body. The WBGT is especially useful for keeping athletes safe on hot days. 

Those two metrics often lead to confusion for the general public. Making matters worse is the widely believed lie that the heat index is "made up" for ratings (oh brother).

HeatRisk seeks to cast aside those ignorable digits in favor of an easy-to-understand scale that can help everyday folks use the forecast to stay safe, with the added benefit of alerting local officials and hospitals that they may need to provide relief and assistance to those who need it the most.

Right now, HeatRisk forecasts are still in the "experimental" stage. The NWS often introduces new products like this as experimental services that aren't used in everyday forecasting and decision-making.

You can provide feedback on the HeatRisk program directly to the NWS, and they'll use all the comments, concerns, and suggestions they receive to tweak the product before making it an official service.

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Severe thunderstorms might blot out the eclipse for parts of the U.S.

A long-duration spell of rainy, stormy weather will cover much of the southern United States through the upcoming week, kicking off with a round of severe thunderstorms on the southern Plains on Monday.

Did you know there's also a total solar eclipse happening on Monday? I know! They kept that secret really well.

It's going to be a strange day across the area as thunderstorms are expected to coincide with the moon's shadow as it passes over the region, blotting out the sun for several minutes along the path of totality.

Some lucky folks in Texas, Oklahoma, and Arkansas will see three to four full minutes of night-like darkness at the peak of the eclipse early Monday afternoon, complete with colors on the horizon that make it appear as if you're surrounded by a 360° sunset.

Millions of visitors are flocking to the path of totality across the U.S. and Canada hoping to catch a glimpse of the special moment. Darkness descends regardless of cloud cover, but folks who manage to see the total eclipse amid clear skies will experience a once-in-a-lifetime moment.

The position of the total solar eclipse in five-minute increments, overlaid on the SPC's severe weather outlook for Monday.

But those pesky clouds are likely going to get in the way for much of the eclipse's track across the southern U.S.

A trough digging across the southern Rockies to begin the week will kick off a round of strong to severe thunderstorms throughout the southern Plains. Widespread severe weather is expected through Monday afternoon and evening, according to the Storm Prediction Center. Much of the action will focus on Texas, with a risk for severe storms spilling into neighboring states.

Damaging wind gusts and "very large" hail are the predominant risks with Monday's storms, the SPC said in its outlook on Saturday. This is a little riskier than normal given the number of people visiting the region. The risk for traffic jams is bad news on a normal severe weather day, let alone when there's a hailstorm during a mass exodus.

Hightailed it south at the last minute to escape a thunderstorm and catch eclipse. Temp dropped 8°F. Light changed. So glad I got to see it. pic.twitter.com/G5kmD9FGI5

— Dennis Mersereau (@wxdam) August 21, 2017

View-wise, it's not the end of the world if your view of the eclipse is obscured by clouds. Storms popped up here in North Carolina during the August 2017 eclipse. We had 94 percent coverage of the sun at the peak of the eclipse, and I could still see the crescent sun through the storm clouds that day.

If nothing else, this will be an interesting case study for how the eclipse affects active weather. I wrote a bit about how eclipses affect the weather for The Weather Network last year.

Temperatures noticeably drop along the path of totality, so much so that we see fair-weather cumulus clouds dissipate for several hours in the wake of the moon's shadow. The temporary loss of daytime heating may have a tiny effect on any thunderstorms ongoing during totality.

Looking beyond the eclipse, stormy weather will continue throughout the week as a robust and slow-moving low-pressure system develops.

Aside from the risk for more rounds of  severe thunderstorms, we could see a threat for widespread flooding 3-5+ inches of rain falls on a huge swath of the south and Ohio Valley through the end of the week.

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Widespread severe thunderstorms expected overnight into Tuesday

We're in the midst of the first widespread severe weather outbreak of the season across a large swath of the central United States as a feisty low-pressure system cuts across the region.

The Storm Prediction Center issued a moderate risk—a 4 out of 5 on the scale measuring the risk for severe weather—for Oklahoma on Monday and again for much of Ohio on Tuesday. These are the first moderate risks issued anywhere in the U.S. since August 7 of last year.

All modes of severe weather are likely with the storms that fire up over the next couple of days. We've already seen multiple severe thunderstorms roll across the southern Plains and the Midwest on Monday, with plenty of large hail and a few reported wind gusts of 70+ mph.

The Setup

The hubbub is the result of a low-pressure system trucking across the central Plains tonight. This low will continue strengthening as it heads toward the Great Lakes into Tuesday.

The Weather Prediction Center's surface forecast for Tuesday afternoon.

It's the classic springtime severe weather setup. A steady stream of warm, humid air flowing out of the Gulf will provide ample fuel for thunderstorms to flourish as this system moves through the region.

Upper-level winds are favorable for thunderstorms to quickly turn severe, growing into both supercell thunderstorms and robust squall lines.

Safety Tips

This is our first widespread severe weather outbreak in a while. Anxiety is high, made worse by social media storm enthusiasts who treat it like an adrenaline sport.

Not everyone under the risk for severe weather will get hit by severe weather. Keep an eye on the radar, look out for severe weather alerts, and have a plan ready to take shelter from bad storms whether you're at home, work, school, or even the grocery store.

Strong winds are the single greatest threat to safety during severe weather—almost entirely due to trees blowing into homes and vehicles. If you live in an area at risk for overnight severe weather, please consider sleeping in a room where trees or tree limbs don't loom outside. 

Make sure you have a way to receive severe weather alerts when you're asleep, and ensure that emergency alerts for tornado warnings are activated on your smartphone. These noisy push alerts can provide critical moments of heads-up before bad weather arrives.

Round One: Monday Night into Tuesday

Our first round of storms was already in progress by the time this post went live around 8:30 p.m. Eastern on Monday.

Multiple supercells in Texas, Oklahoma, and Kansas left behind large hail and wind damage in their wake. Supercells are thunderstorms with rotating updrafts, a feature that makes these storms resilient and capable of producing more intense severe weather.

As we so often see during these outbreaks, these supercell thunderstorms will eventually merge into a long, broken squall line that'll chug east through the overnight hours. 

Forecasters expect these storms to continue producing widespread severe weather across Missouri, Arkansas, and Illinois overnight Monday and into early Tuesday morning.

A model image showing a potentially severe squall line around 2:00 a.m. CDT on Tuesday. (WSV3)

The main threat with the overnight squall lines will be damaging straight-line winds, with many of the storms capable of producing significant wind gusts of 75+ mph. These storms will push east through early Tuesday morning, likely reaching Indiana and Ohio in time for the morning commute.

There's also a risk for tornadoes embedded in these squall lines—you'll sometimes hear them called "QLCS tornadoes," taking their name from the technical term for a squall line. These tornadoes happen quickly and often with reduced tornado warning lead time.

Round Two: Tuesday

We'll see the low-pressure system moving into the lower Great Lakes during the day Tuesday, dragging a cold front into a vast plume of warm, humid air parked over the region.

Forecasters expect the atmosphere to recover from Tuesday morning's storms in time for a fresh round of severe thunderstorms to build over the Ohio Valley and Mid-South by the afternoon hours.

A model image showing the general areas where we might see severe storms around 5:00 p.m. EDT Tuesday. (WSV3)

The strongest thunderstorms are likely over eastern Indiana and much of Ohio covered by the moderate risk. Dynamics here are favorable for supercells that would be capable of producing tornadoes—some of which could be strong and long-lived—as well as hail larger than golf balls and damaging wind gusts.

Farther south, storms are likely to form into one or more squall lines as they push through Kentucky, Tennessee, and northern Alabama. Damaging winds and embedded tornadoes would be the predominant threats with these storms. 

The risk for severe weather will continue pushing east overnight Tuesday into Wednesday, with severe storms possibly crossing the Appalachians and heading into the Virginias and Carolinas. Damaging winds and an isolated tornado would be the main threat with these remaining storms.

[Satellite image via NOAA]

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