LITTLE ROCK, Ark. – February 28- March 6, 2021, has been declared Severe Weather Awareness Week by the National Weather Service (NWS) and the Arkansas Department of Emergency Management (ADEM). Today’s topic of discussion is tornadoes.
A tornado is formed when differing wind speeds at the surface and a few thousand feet up to help create a rotating horizontal tube of air. As a thunderstorm moves into the vicinity of this horizontal rotating column of air, it will ingest it and tilt it vertically. Mechanics inside a thunderstorm will then stretch this column of rotating air, causing it to spin faster and extended out of the cloud base.
If this rotating column of air does not reach the ground, it is a funnel cloud. Only when the rotating column of air comes into contact with the surface will it become a tornado.
Tornadoes are violent and sometimes unpredicatble in their movement.
Forecasting for tornadoes has come a long way, though brief, weak tornadoes can still form so quickly that radar barely picks up its signature.
Arkansas has two severe weather seasons in which tornado frequency increases- spring and fall. While that may be the case, it is important to note that tornadoes can happen during any month of the year.
It’s during these seasons when warm and cold air masses collide and have the most prevalent ingredients for tornado formation. Those ingredients include but are not limited to moisture, wind shear (winds differing in speed and/or direction), instability (energy potential), lifting mechanism (cold fronts).
In 2020, 45 tornadoes occurred in Arkansas, which is 12 above the average count (33) for the state. The most active months were January with 11 tornadoes and May with 9 tornadoes. The third busiest months were March and August with 8. August was a unique month because all tornadoes occurred from tropical systems that were moving over Arkansas.
Most tornadoes in Arkansas have been low-end or considered weak (below EF-2 rating). According to data from the local NWS office, 68% of the tornadoes that have occurred in Arkansas since 1950 have been rated EF-0/EF-1, 23% percent have been EF-2 and less than 10% are rated EF-3 or higher.
Strong and violent tornadoes, rated EF-4 and EF-5, are pretty rare. Only 1.5% of all tornadoes were rated EF 4. Since 1950, there have been no EF 5 tornadoes ever recorded in Arkansas.
The last EF 4 tornado in the state was on April 27, 2014. It tracked through Pulaski, Faulkner, and White counties, leaving a path 41 miles long and killing 16 people.
Looking ahead to 2021 Spring Season:
While statistically proven that the frequency of severe weather including tornadoes increases during the months of March, April and May, certain weather patterns like El Nino or La Nina can have an impact on that frequency.
During an El Nino phase, this pattern can help lessen the frequency of severe weather like tornadoes and hail as shown above.
In a La Nina phase, this pattern can cause the standard frequency of severe weather to have the odds of becoming even more frequent.
As we head into the Spring season, we will be in a La Nina pattern so a higher frequency of severe weather than what we normally see is possible. Again, being in one of these patterns does not guarantee higher or low frequency but increases the probability of either outcome.
While reading about the stats above, the thought about what EF stands for might have come across your mind. EF stands for Enhanced Fujita. Fujita comes from Dr. Ted Fujita who helped create the original damage scale back in 1971. In 2007, the scale was modified to account for enhancements in building design, vegetation, and other variables.
A tornado cannot be given a rating until damage from it is assessed. From there, the amount and type of damage can be translated to the wind speeds that caused it.
When severe weather is in the forecast, it’s important to know the difference between critical weather terminology and what you should do for each scenario. A few terms in particular can cause some confusion when tornadoes are mentioned in the weather forecast.
A Tornado Watch means that conditions are favorable for the development of a tornado, but it does not mean that a tornado is on the ground.
- Preparations: review your severe weather safety plan, and make sure you’re staying weather-aware throughout the day.
A Tornado Warning means that a tornado has been sighted or has been indicated on radar. Danger may be imminent.
- Take action: seek shelter immediately.
The term Tornado Emergency is reserved for rare situations in which a tornado has been spotted visually or radar strongly suggests the ongoing destruction of a tornado (debris ball signature indicating debris being lofted into the air, picked up on radar technology). The NWS uses this term when there is a severe threat to human life and catastrophic damage is likely ongoing.
- Take action: seek shelter immediately.
If there is severe weather in the forecast, or if a tornado watch has been issued, follow these guidelines to prepare for a warning:
- Have a reliable way to receive tornado warnings (TV, NOAA Weather Radios, Weather Apps with alerts/notifications turned on, following professional sources on social media).
- Have a map readily available to reference cities and counties to reference where you are
- Charge electronic devices.
- Gather flashlights and batteries in case power goes out.
- Collect blankets, bike helmets, food to place in your safe space.
What to do when a tornado warning is issued?
- Seek shelter in a basement or storm shelter.
- No basement or storm shelter? No problem. Head to the lowest level and innermost room, putting as many walls between you and the outside as you can.
- Stay away from windows and doorways.
- Get low and protect your head using blankets or bicycle helmets if nearby.
- If you’re driving, pull over and seek shelter in the nearest building.
- Do not park under bridges or overpasses. They act as a wind tunnel, increasing the speed of wind underneath the road. Debris can get lodged in the “tunnel”, making it unsafe. Plus, emergency vehicles will need to get by and stopping here leads to traffic.
- If you live in a mobile home, even if it is tied down, you are not safe. Abandaon it immediately and seek shelter in sturdier building.
Many towns and counties have an outdoor tornado siren system that is used to alert the public when a warning has been issued. These sirens are only to alert people who are outdoors. Therefore, it is not a reliable source for tornado warning alerts.
The National Weather Service is the organization responsible for issuing the warnings, however, it has no control over the sirens. City and county officials make the call on sounding the siren.