What Technology Tools Do Meteorologists Use To Monitor Tornadoes
Julia Kozub
Thunderstorms occur in all 50 states. They can occur, at any time, day or night, throughout the entire year. Thunderstorms are most common in the late afternoon and evening during the warm months. It has been estimated that 1800 thunderstorms are in progress at any given moment around the world and that lightning strikes the earth 100 times every second. Thunderstorms are basically beneficial providing necessary rainfall. In the United States, only about five percent of thunderstorms become severe and only about one percent produce tornadoes.
A list of weather brochures and learning aids are available at
Your local National Weather Service Office provides severe weather spotter training under a program called SKYWARNTM. It is provided free-of-charge with the request that when you do encounter severe weather, you report it to the National Weather Service. The spotter training class includes computer and video presentations that help you learn how to pick out visual clues from clouds to help determine the severity of a storm and other tips on reporting hazardous weather. It is highly recommended that the assigned district "Severe Weather Administrator and each school assigned "Severe Weather Coordinator" take the training. Although, any number of teachers and administrators are welcome to attend and receive the training. The enclosed books provide information about storms and spotting, however, they are not a substitute for official training.
what technology tools do meteorologists use to monitor tornadoes
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The National Weather Service uses a combination of radar, satellite, lightning detection, and surface observations, including volunteer spotter reports for detecting and tracking severe weather. The new sophisticated Doppler radars (WSR-88D) around the country have greatly increased the National Weather Service's ability to pinpoint severe thunderstorms and possible tornadoes and warn the public as to where the storm is moving and what actions to take. Spotter reports tell forecasters the size of hail, the depth of snow or flood waters, if wind damage is occurring, or if a tornado is sighted. These reports provide ground truth to the images seen on the Doppler radar.
The WSR-88D (Weather Surveillance Radar - 1988 Doppler) is the new radar system for NWS, the Federal Aviation Administration, and the Department of Defense (DOD). It is a very sensitive radar designed specifically for the detection of weather phenomena. The computers that compile the radar data can produce as many as 100 different radar products every 5 minutes for forecaster interpretation.
Typically radar has been used to tell meteorologists where precipitation is occurring, how intense it is, and where it is moving. The ability of the new radars to detect radial velocity (movement of radar targets, such as rain, toward or away from the radar derived from the "Doppler Effect") allows meteorologists to see rotation of thunderstorm updrafts and sometimes the development of tornadic circulation. Supercell thunderstorms displaying strong radar signatures (storm rotation) may allow forecasters to provide up to 20 minutes lead-time on warning for a tornado before it touches down. Computer and mapping skills with the new radar system also help meteorologists determine rainfall amounts and pinpoint areas with potential flash flood problems.
Like all technology, radars have their limitations. Radar beams can not see through mountains. This means that weather at the valley floor between mountain ranges will not be detected. Because of the curvature of the earth, as the radar beam moves away from its source, it gets higher and higher in the atmosphere and is no longer sampling the lower portion of the storm clouds. The NWS compensates by using trained severe weather spotters which help forecasters to fill in the gaps and provide ground truth information.
Geostationary satellites (stationary above a point over the equator) and polar orbiting satellites allow meteorologists to watch the development of clouds and weather systems. Satellites are extremely useful for tracking weather systems over the vast ocean areas where no radar exist and only a few surface observations are taken. For example, satellites greatly improved meteorologists' ability to detect the formation and movement of hurricanes over the tropical waters. Satellites also help meteorologists to track movement of air masses that are either very dry (such as off the mountains) or very moist (such streams from the Eastern Pacific Ocean). This can greatly influence a storm's development. Cloud patterns also tell forecasters about the strength and movement of the jet stream which plays a large role in storm development.
While satellites provide meteorologists with much information, they also have limitations. The satellite views a cloud from above, but does not tell what has formed below it (such as a tornado). Severe thunderstorms and tornadoes can develop and dissipate fairly rapidly. Even if a satellite picture indicated a severe storm, the time delay for receiving the satellite picture may be 15 to 30 minutes which can be too long to properly warn for an event such as this.
Lightning detection systems map where cloud-to-ground lightning strokes are occurring. While this allows meteorologists to know that thunderstorms are indeed in progress and the frequency of lightning strokes, it tells little about the severity of the thunderstorm. People often report "vivid lightning" or "severe lightning," but lightning is not a criterion for whether a storm is severe, according to the NWS definition of "severe." Lightning assists forecasts in preparation for Fire Weather Forecasts and Products used by land management agencies and local fire fighters.
Surface observation are the "ground truth" for tools such as radar and satellite. Because thunderstorms are very localized (the severe weather potion of the storm may only affect an area one mile wide), it would be impossible to have weather observers everywhere.
It is the combination of surface reports and remote sensing tools that brings the entire picture together for forecasters and increases their ability to issue effective, informative, and timely warnings. While the new technology has enhanced the meteorologist's ability to issue a timely warning, it will be of little use if the people who receive the warning do not know what safety actions to take.
Since tornadoes form from the bottom of a thunderstorm, a satellite can't "see" tornadoes. However, pre-tornadic conditions such as overshooting tops on visible and IR images or an unstable atmosphere depicted by satellite sounder profiles are always available.
To look at a storm from the surface up to the bottom of a cloud, meteorologists rely on another remote sensing device that detects microwave energy, or weather radars. Radar is an acronym for "radio detection and ranging." Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. The strength and origin of "echoes" from objects hit by the microwaves is received by computers attached to the originating radar and monitored by meteorologists. A Doppler radar can detect wind speed and direction, rotation often signifies tornadic development.
Once a tornado is detected, both radars and satellites are used to track the storm. Satellite images often show details of tornado damage, especially from high resolution POES images as seen below.
Fade between before and after images to see the path of the Siren tornado in northern Wisconsin from 2001. Traveling from west to east, the twister killed three people, destroyed homes, uprooted trees, and flattened crops.
Besides weather satellites, atmospheric measurements, and computer models, meteorologists use weather radar to monitor and forecast the weather. Weather radar provides important information on where rain or snow is falling. Looking at several radar images over a period of time can give clues about where and how fast the rain or snow is moving. A loop of several images can also help show if the rain or snow is growing or shrinking in area or if it is becoming more intense.
Coarse low resolution radar images similar to those that would be present during 1970s. Left: radar image of severe thunderstorm from 1960s and right: 74C radar image of squall line with trailing area of light rain. Source for both images is medialine.com
Today's weather radars operated by the National Weather Service are highly sensitive and include Doppler capabilities. They provide fine resolution measurements of reflectivity and velocity and multiple categories of analysis products. Data and information from these radars allow forecasters to look inside storms and infer wind speed and direction.
Additionally, an upgrade to dual polarization products in all National Weather Service radars in 2012-2015 allows forecasters to better determine atmospheric target type, size and diversity. These new dual polarization capabilities allow forecasters to better identify precipitation type, which ultimately helps with winter weather forecasting and hail detection, improves precipitation estimation, filters out non-meteorogical targets so forecasters can only focus on meteorological phenomena, and identifies airborne debris which can assist in locating tornadoes.
Dual Polarization improvements to the NWS radars occurred in 2012-2015. Image at left shows the algorithm that indicates the most likely precipitation type. Image at right shows different dual polarization elements for a tornadic thunderstorm. Source for both images is NWS Jackson, MS.
While radar displays in 1975 were different shades of gray, radar displays today are in digital format with advanced color curves to highlight specific features. In 1975, the radar meteorologist had to manually trace the outline of rain and snow areas on an overlay to see where it was. Today's radars use geographic information systems (GIS) to allow for quick identification of storms and rain or snow areas near various cities or towns, parks, rivers, and highways. Radar data today can also be merged with other data types such as satellite cloud top temperatures and lightning strikes to determine the trend of a storm and to estimate rainfall rates and hail size within the storm.
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