Tornado season doesn’t officially begin until late April or early June, but it’s time to think about it. Although, here in Terry County and surrounding counties, there has not been much measurable rain and it looks like a severe drought might plague our area soon. Howevr, tornado’s can happen in a small thuinder storm.
What is a tornado?
A tornado is a narrow, violently rotating column of air that extends from a thunderstorm to the ground. Because wind is invisible, it is hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris. Tornadoes can be among the most violent phenomena of all atmospheric storms we experience.
Where do tornadoes occur?
Tornadoes occur in many parts of the world, including Australia, Europe, Africa, Asia, and South America. Even New Zealand reports about 20 tornadoes each year. Two of the highest concentrations of tornadoes outside the U.S. are Argentina and Bangladesh.
How many tornadoes occur in the U.S. each year?
About 1,200 tornadoes hit the U.S. yearly. Since official tornado records only date back to 1950, we do not know the actual average number of tornadoes that occur each year. Plus, tornado spotting and reporting methods have changed a lot over the last several decades, which means that we are observing more tornadoes that actually happen.
Where is Tornado Alley?
Tornado Alley is a term coined by the media to describe a vast region in the central United States that experiences a relatively high frequency of tornadoes. Various maps labeled as “Tornado Alley” can differ significantly because tornado occurrences can be measured in several ways: by all tornadoes, by specific tornado county segments, by focusing only on strong and violent tornadoes, and by using different databases over various time periods.
However, the concept of “Tornado Alley” can be misleading. The tornado threat in the U.S. shifts seasonally; it moves from the Southeast during the cooler months to the southern and central Plains in May and June, and then to the northern Plains and Midwest during early summer. Tornadoes can and do occur in all fifty states.
It’s important to remember that violent tornadoes also happen outside of “Tornado Alley” every year.
When are tornadoes most likely?
Tornado season generally refers to the time of year when the United States experiences the highest frequency of tornadoes. For the southern Plains states, such as Texas, Oklahoma, and Kansas, the peak tornado season occurs from May to early June. In contrast, the Gulf Coast typically sees tornadoes earlier in the spring. In the northern Plains and upper Midwest, which includes North and South Dakota, Nebraska, Iowa, and Minnesota, tornado season usually takes place in June or July. However, it’s important to note that tornadoes can occur at any time of year and at any time of day or night, although most tornadoes tend to happen between 4 p.m. and 9 p.m.
What is the difference between a Tornado WATCH and a Tornado WARNING?
A Tornado WATCH is issued by meteorologists at the NOAA Storm Prediction Center, who monitor weather conditions 24/7 across the entire U.S. for the potential of tornadoes and severe weather. A watch can cover parts of a state or multiple states. During a watch, it is important to prepare for severe weather and stay updated via NOAA Weather Radio for any warnings that may be issued.
A Tornado WARNING is issued by local meteorologists at your NOAA National Weather Service Forecast Office, who observe weather conditions 24/7 in a specific area. A warning indicates that a tornado has either been reported by spotters or detected by radar. This means there is an immediate and serious threat to life and property for those in the tornado’s path. A tornado warning signifies that you should ACT NOW to find safe shelter! Warnings can cover parts of counties or multiple counties within the danger zone.
How is tornado strength rated?
To determine the strength of a tornado, experts analyze the damage it causes. This information allows us to estimate the wind speeds associated with the tornado. In 2007, the National Weather Service introduced the “Enhanced Fujita Scale” (EF-Scale) to provide a more consistent and accurate rating of tornadoes. The EF-Scale considers more variables than the original Fujita Scale (F-Scale), incorporating 28 different damage indicators, such as the types of buildings, structures, and trees affected.
For each damage indicator, there are eight levels of damage, ranging from the first signs of damage to complete destruction. The original F-Scale did not account for these details. Although the historical data of the original F-Scale will remain unchanged—meaning that a tornado rated as an F5 years ago will still be considered an F5—the wind speed associated with that tornado may have been overestimated.
A correlation has been established between the original F-Scale and the EF-Scale, allowing for ratings to be expressed in terms of either scale while preserving the historical database.
How do tornadoes form?
The truth is that the understanding of tornado formation is still incomplete. The most destructive tornadoes typically form from supercells, which are rotating thunderstorms characterized by a well-defined radar circulation known as a mesocyclone. Supercells can also produce damaging hail, severe non-tornadic winds, frequent lightning, and flash floods.
Tornado formation is believed to be primarily driven by phenomena occurring at the storm scale, particularly within and around the mesocyclone. Recent theories and findings from the VORTEX2 program suggest that once a mesocyclone is established, the development of a tornado is influenced by the temperature differences across the edge of the downdraft air that wraps around the mesocyclone. However, mathematical modeling studies have shown that tornado formation can occur even without these temperature patterns. In fact, very little temperature variation was observed during some of the most destructive tornadoes in history, such as the one on May 3, 1999.
Clearly, we still have a lot of work to do in understanding tornado formation.
What do storm spotters look for when trying to identify a tornado or a dangerous storm?
Inflow bands are irregular formations of low cumulus clouds that extend from the main storm tower, typically toward the southeast or south. The appearance of inflow bands indicates that the storm is drawing in low-level air from a distance of several miles. If these inflow bands exhibit a spiraling pattern, it suggests that there is rotation within the storm.
The beaver tail is a smooth, flat cloud band stretching from the rain-free area’s eastern edge to the east or northeast. Typically, it runs along the southern edge of the precipitation zone and indicates a potential rotation in the atmosphere..
A wall cloud is an isolated cloud that hangs down from the rain-free base of a thunderstorm. It is typically located behind the area where rainfall is occurring. A wall cloud capable of producing a tornado can form 10 to 20 minutes before a tornado actually touches down, although this is not always the case. A wall cloud may exhibit persistent rotation (often visible), experience strong surface winds flowing into it, and show rapid vertical motion, which is indicated by small cloud elements quickly rising into the rain-free base.
As the storm intensifies, the updraft pulls in low-level air from several miles around. Some of this low-level air is drawn into the updraft from the rain area. This rain-cooled air is very humid, and the moisture quickly condenses below the rain-free base, forming a wall cloud.
The rear flank downdraft (RFD) is a downward rush of air located on the back side of a storm, descending alongside a tornado. The RFD appears as a “clear slot” or “bright slot” just to the rear (southwest) of the wall cloud. It can also resemble curtains of rain wrapping around the circulation at the cloud base. The RFD produces gusty surface winds that sometimes include embedded downbursts. This downdraft is responsible for the hook echo feature observed on radar.
A condensation funnel consists of water droplets and extends downward from the base of a thunderstorm. If the funnel makes contact with the ground, it is classified as a tornado; if it does not touch the ground, it is referred to as a funnel cloud. The presence of dust and debris beneath the condensation funnel indicates that a tornado is present.
Be careful! Tornadoes can form and be in contact with the ground without a fully condensed funnel!
