Tornado Forecasts

An example of a radar hook echo Click on image for full size (28K JPEG) and description Image courtesy of NWSFO/Tusla, OK Tornadoes are hard to forecast. They don't last very long so there's not much time to figure out what's happening. Also, scientists don't really know how they form. They know what the weather's like when past tornadoes have formed, so that's what they use to make forecasts. Meteorologists take measurements of the air called soundings. One of the things these measurements tells them is how stable the air is. Other measurements tell them the temperature and humidity. Using these measurements, meteorologists can tell if tornadoes are likely to form. When an area looks like it might get hit, they issue a tornado watch. By using a new kind of weather radar, meteorologists can detect a tornado as it's forming--up to 20 minutes before it forms a funnel! Using conventional radar, they might have been able to see the tornado after it already formed. (A tornado would show up as a hook echo.) That doesn't leave much time to issue a tornado warning. Also, tornadoes don't always show up on radar. Tornado spotters are needed to give reliable observations of the weather. The more time people have before a tornado, the fewer people will be hurt or killed because they'll have more time to seek shelter.

Tornado Forecasts

An example of a hook echo Click on image for full size (28K JPEG) and description Image courtesy of NWSFO/Tusla, OK It's hard to forecast tornadoes. They don't last very long and are also very complicated. Scientists don't really know how they form, but they do where they tend to form. Using what they know about the atmospheric conditions from past tornadoes, meteorologists can tell when they may form. Every twelve hours, meteologists send up weather balloons to take what is called a sounding of the atmosphere. The balloons carry equipment to measure conditions such as atmospheric stability, temperature, and humidity. Using these measurements, forecastors can tell if a tornado is likely to form. Some of the conditions that are needed are high instability and high humidity. If these conditions exist, they will issue a tornado watch. Using a new kind of weather radar, meteorologists can detect a tornado as it's forming--up to 20 minutes before it touches down! With conventional radar, they usually could only detect a tornado only after it had formed. The tornado would appear as a hook echo on the radar return. This also wasn't reliable so forecastors had to rely on spotter reports. The new radar gives forecastors the lead time they need to issue a tornado warning early enough that the public can seek shelter.

Tornado Forecasts

An example of a radar hook echo Click on image for full size (28K JPEG) and description Image courtesy of NWSFO/Tusla, OK The short duration and complicated nature of tornadoes make them nearly impossible forecast. Meteorologists don't really know the specifics of how they form, but they do know what atmospheric conditions were present during past tornadoes. They use this knowledge to try and identify tornado threats before they happen. The earlier they realize that a tornado is going to strike, the earlier they can notify residents of the areas which will be hit. The more warning people have, the fewer people will be killed. To know the current atmosphere conditions, meteorologists send up weather balloons every twelve hours to take soundings of the upper atmosphere. The equipment on the balloons measure conditions such as the atmospheric stability, temperature, and relative humidity. Two conditions tornadoes need to form are high instability and a high dew point. When these conditions exist, they issue a tornado watch. A new type of weather radar can greatly improve the time between tornado detection and tornado touchdown. Conventional radar could only be used to detect a tornado after it had formed, usually by seeing a shape such as a hook echo on the radar return. The echo doesn't appear with every tornado, so forecastor can't rely on just that information. They also need observations from tornado spotters in order to issure a tornado warning.

Last modified prior to September, 2000 by the Windows Team

The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer