Tornadoes: When, Where & Why?
Why do tornadoes form?
Tornadoes are formed due to large super cells. Super cells are nothing but a huge cluster of thunderstorm clouds. A simple explanation to its formation is as follows: warm air rises up as it has a low vapor pressure and cold air drops down because of its high vapor pressure. Due to this, the warm air in the end forms a vortex and forms a funnel cloud, otherwise known as a tornado. A characteristic green color appears in the sky when a tornado is completely formed and ready for destruction.
The formation of tornadoes is followed in a set pattern of simple steps.
Firstly, when the thunderstorm approaches, the wind direction speed changes in the upper area of the atmosphere and causes an invisible horizontal spinning effect in the lower region.
Secondly, the horizontal air is tilted to vertical because of the rising hot air’s updraft. It eventually forms into a spiral with diameter ranging from 2-6 miles of rotating air.
Thirdly, a rotating wall cloud originating from the center of the storm (eye of the storm) is formed as the base cloud. This region is rain-free. Just moments later, a tornado is formed and it starts revolving around violently at high speeds and cause havoc in and around the environment.
Where do tornadoes happen?
- Occur in every state
- About 800 reported every year
- About 180 people killed every year
- Season runs March – August but tornadoes can occur any time of year
- Can occur any time of day but most likely to occur 3:00 p.m. to 9:00 p.m.
- Annual damage can be hundreds of millions
Computer forecast models
Meteorologists often rely on massive computer programs called numerical weather prediction models to help them decide if conditions will be right for the development of tornadoes. These models are designed to calculate what the atmosphere will do at certain points over a large area, from the Earth’s surface to the top of the atmosphere. Data is gathered from weather balloons launched around the globe twice each day, in addition to measurements from satellites, aircraft, and temperature profilers and surface weather stations. The models start with these current weather observations and attempt to predict future weather, including supercells, using physics and dynamics to mathematically describe the atmosphere’s behavior. The predictions are usually output in text and graphics (mostly maps).
Computer models work great if the weather follows the rules we have set. When the weather breaks the rules, the predictions have trouble too. Another technique being developed is the concept of “ensemble forecasting.” Instead of using just one model, a supercomputer runs several models at one time – an ensemble. If each run looks similar, then we can assume the weather will likely follow the rules. If the runs look different in different places, then we understand that something in the atmosphere is causing the weather to misbehave.
Another technique is to run the same model several times with varying starting weather conditions. This approach results in a number of predictions that produce a range of possible future weather conditions.
Interpreting the model output is key, and takes a lot of practice. Forecasters use their experience, knowledge, persistence (what makes us think the weather is going to change from what it is now?) and eyes (looking out the window!) to fine-tune their forecasts. An important advancement has been made in model displays – the output used to be on black and white maps. Now forecasters can look at the output on their computer workstations and use different colors to understand more clearly what is happening.
- A highway overpass is a safe place to take shelter under during a tornado
- Opening windows during a tornado will help balance the pressure between the inside and outside of the house and may prevent destruction of the structure
- One should seek shelter in the southwest corner of a house or basement.
- During any storm, listen to local news or a NOAA Weather Radio to stay informed about tornado watches and warnings.
- Know your community’s warning system. Communities have different ways of warning residents about tornadoes, with many having sirens intended for outdoor warning purposes.
- Go to a pre-designated area such as a safe room, basement, storm cellar, or the lowest building level. If there is no basement, go to the center of a small interior room on the lowest level (closet, interior hallway) away from corners, windows, doors, and outside walls. Put as many walls as possible between you and the outside. Get under a sturdy table and use your arms to protect your head and neck.
- In a high-rise building, go to a small interior room or hallway on the lowest floor possible.
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