Nighttime Tornadoes More Than Twice as Likely to Be Deadly

Tornadoes at night are more than twice as likely to be deadly as those during the day, according to a study.

After examining roughly 48,000 tornadoes in the United States from 1950 to 2005, the study led by Walker Ashley from Northern Illinois University found that roughly one in every 20 overnight tornadoes were killers, compared to roughly one in every 50 daytime tornadoes.

Nocturnal tornadoes only make up about 27% of all tornadoes but are responsible for 39% of tornado deaths and 42% of killer tornadoes in that 55-year period.

Why More Nighttime Deaths?

Some reasons for this are more obvious.

Unless lit by at least somewhat frequent lightning, you may not see a tornado at night. One challenge the meteorological and social science communities face is getting the public to take shelter immediately, without first "confirming the threat" of a tornado by looking outside and wasting precious seconds to reach shelter.

Fewer storm spotters may be willing to take the risk of storm chasing at night, reducing the ability of meteorologists to confirm tornadoes in progress at night.

Most people are at home and asleep at night and can be unaware of an approaching tornado threat.

That's why it's so important to have multiple ways to receive tornado warnings. This could include a NOAA weather radio or your smartphone.

Where Nighttime Tornadoes Are Most Common

A disconcerting finding in the study is that for many of the most tornadic states in the U.S., a sizable number of tornadoes occur at night.

One-third to just under one-half of all tornadoes in 11 states from Oklahoma to West Virginia from 1950 to 2005 touched down at night, according to the study.

The state with the greatest percentage of nighttime tornadoes is Tennessee, with 46% of all tornadoes there coming at night.

Add population growth in the South, primarily in large cities and their suburbs, and you can understand the overall increasing vulnerability of this region to these events.

Nighttime Tornadoes a Year-Round Concern in the South

Unlike other parts of the country enduring harsh winter cold that eliminates the instability needed, tornadoes can be a concern any time of year in parts of the South. 

Thus, given the fewer hours of daylight, contributed to by standard – rather than daylight – time, any cold-season Southern tornadoes have a greater chance of occurring after sunset.

Even the core winter months of December through February have averaged three to six nocturnal tornadoes in the U.S. from 1953 through 2015, according to NOAA's Storm Prediction Center.

There's also a pronounced nighttime tornado maximum in November, coinciding with the often-discussed "second season" for severe weather targeting the Deep South. 

These colder-month tornadoes often occur with a very strong jet stream, meaning winds aloft can move the parent supercells or squall lines in which these tornadoes are embedded at speeds of 60 mph or more, giving little time to seek shelter.

Also, the public's overall awareness of severe weather may not be as high during the winter months, even in areas that can and do experience severe weather any month of the year.

What You Can Do

How can you be warned if you're sound asleep? Here are some tips:

-Buy a NOAA weather radio. You can find these at most electronics retailers. They feature warning alarms that can be set to sound loudly when any National Weather Service tornado or severe thunderstorm watch or warning is issued.-Your smartphone can alert you. Most newer smartphones are capable of receiving wireless emergency alerts from your local NWS office. These include tornado warnings. Make sure your smartphone is charged sufficiently and left on overnight, and a special tone and vibration will occur twice when a tornado warning is issued. Note, however, this will not sound for a tornado watch or severe thunderstorm warning.-Other weather apps can also alert you. Many weather apps, including The Weather Channel app, can also send alerts to your smartphone, tablet or smartwatch.-Know where to go. Have a plan in place in advance for where you will seek shelter.

In general, your awareness of the threat of overnight severe weather, before you go to sleep, is very important. 

Is a severe thunderstorm or tornado watch extending into the overnight hours? Or is there a threat of severe weather developing overnight? Make sure your weather radio or smartphone is ready to alert you. It may save your life.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.