Q: How do radars see tornadoes?
A: A weather radar consists of a transmitter and a receiver. The transmitter emits pulses of radio waves outward in a circular pattern. Precipitation scatters these radio waves.
“Reflectivity” is the amount of transmitted power returned to the radar and measured by its receiver. The intensity of this received signal indicates the intensity of the precipitation.
Measuring the time it takes for the radio wave to leave the radar and return tells us how far away the storm is. The direction pointed by the radar locates the storm.
Dirt, plant matter, and other debris thrown into the atmosphere by a tornado on the ground can be detected by radar.
NATIONAL WEATHER SERVICE
A hook echo is a pattern in a reflectivity image. It looks like a spiral rotating outward clockwise, with the precipitation “thickness” increasing – or, a hook shape. This pattern suggests that the storm is rotating and may produce a tornado. A tornado could be found at the narrow top of the spiral.
Doppler radars measure the speed at which particles in the cloud are approaching or moving away from the radar. Returning radio waves have a higher frequency if the particles in the cloud are moving towards the radar, and a lower frequency if the particles are moving away. This allows Doppler radars to identify severe weather phenomena. For example, a spinning vortex would have particles no longer moving towards the Doppler radar and then moving away from it a small distance.
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A radio wave is an electromagnetic wave and therefore has electric and magnetic fields oriented perpendicular to each other. This is called polarization. Dual polarization radars measure this polarization and can distinguish between heavy rain, hail, snow and sleet, as well as debris from a tornado.
When a tornado is on the ground, it throws dirt, plant matter, and other debris into the atmosphere. Because the radar is designed to detect the presence of airborne objects, it can show meteorologists where the debris is present and therefore the tornado.
Photos: See the deadly destruction of tornadoes over the years
May 22, 2011: Joplin, Missouri
In this May 25, 2011, photo, Beverly Winans hugs her daughter Debbie Surlin while recovering items from Winans’ devastated home in Joplin, Missouri. The deadliest tornado to hit the United States in decades struck on May 22, 2011, leveling a swath of miles from Joplin and killing 161 people.
AP Photo/Charlie Riedel
April 2011: Southeastern United States
Tuscaloosa Fire Lt. Brian Phillips climbs a pile of rubble to search for survivors or bodies in an apartment building in Tuscaloosa, Alabama, after 362 tornadoes hit the southeastern United States over three days in April 2011, killing about 321 people. Alabama was the hardest hit, with more than 250 dead in that state alone.
AP Photo/Dave Martin
February 5, 2008: “Super Tuesday” outbreak
New cars and trucks at a Chevrolet dealership lie under the wreckage of a tornado that struck Mountain View, Ark., February 5, 2008. The so-called Super Tuesday outbreak of 87 tornadoes in the southeastern states United killed 57 people.
AP Photo/Danny Johnston
April 2014: Southeast and Midwest
An American flag flies from a makeshift flagpole in front of a concrete slab that was once a home in Louisville, Mississippi, after an April 28, 2014 tornado destroyed the home. An outbreak of dozens of tornadoes, fanned by a powerful storm system, hit the Southeast and Midwest over a three-day period in April 2014 and killed 32 people in Iowa, Oklahoma, Arkansas , Mississippi, Alabama and Tennessee.
AP Photo/Rogelio V. Solis
May 20, 2013: Moore, Oklahoma
A tornado killed 24 people on May 20, 2013 in Moore, Oklahoma. The tornado had winds in excess of 200 miles per hour, giving it the most severe rating of EF-5.
AP Photo/Alonzo Adams
March 18, 1925: Missouri, Illinois and Indiana
This March 1925 photo shows an overturned house that was blown more than 50 feet from its foundation following a tornado in Griffen, Ind. The March 18 tornadoes that hit Missouri, Illinois and Indiana killed nearly 700 people, topping the list of the deadliest tornadoes in the United States.
AP Photo
May 11, 1953: Waco, Texas
Supported by heavy equipment, workers begin the mammoth task of clearing the debris left in downtown Waco, Texas from the May 11, 1953 tornado. It was one of 10 tornadoes deadliest in US history, killing 114 people.
AP Photo
November 6, 2005: Evansville, Indiana
While others are intact, debris from destroyed mobile homes litters Eastbrook Mobile Home Park following a tornado in Evansville, Ind., November 6, 2005. The tornado devastated southwest Indiana and northern Kentucky, killing 20, destroying homes and knocking out power to thousands.
AP Photo/Darron Cummings
May 10, 2008: Southwestern Missouri
A vehicle was dropped along Highway 86 north of Racine, Missouri by a tornado that struck the southwestern Missouri area on May 10, 2008. Fourteen people were killed and hundreds injured in the tornado.
AP Photo/Mike Gullett
May 25, 2008: Iowa
The first floor of a home is all that remains September 8, 2008 in Parkersburg, Iowa, more than three months after a May 25 tornado destroyed and damaged hundreds of homes in the area and killed nine people.
AP Photo/Kevin Sanders
February 29, 2012: Illinois
Family and friends try to salvage what they can February 29, 2012 in Harrisburg, Illinois after a tornado destroyed homes in their neighborhood. The devastating EF4 tornado killed eight people.
AP Photo/Seth Perlman
February 11, 2009: Oklahoma
Three-year-old Brooklyn Hickman helps dig through the rubble of his grandfather’s trailer in Lone Grove, Oklahoma on February 11, 2009, after a tornado struck, killing eight people. Weather misfortunes, including an unusual series of February tornadoes, were among Oklahoma’s top stories that year.
AP Photo/Sue Ogrocki
April 28, 2011: Virginia
Downed traffic lights are seen after an EF3 tornado hit April 28, 2011 in Glade Spring, Virginia. Three people were killed and several homes and truck stops along I-81 were badly damaged.
AP Photo/Jeff Gentner
June 8, 1984: Barneveld, Wis.
At dawn on June 8, 1984, rescuers got their first sight of a destroyed Barneveld in Wisconsin. An F5 tornado tore through the village, killing nine people and destroying most of the small community. The powerful tornado had winds of over 300 mph.
Photo from the Wisconsin State Newspaper
May 1955: Udall, Kansas
Photos of destruction from the 1955 tornado that destroyed Udall, Kan., are on display in the city museum. The May 1955 tornado was among the 25 deadliest in US history, killing 80 people.
AP Photo/Charlie Riedel
March 2, 2012: Indiana
People clean up debris from a farm field on the outskirts of Marysville, Ind., after a tornado with 150 mph winds swept through the southern Indiana hamlet March 2, 2012. The storm was part of tornado outbreak that killed 13 people in southern Indiana.
AP Photo/Charles Wilson
October 2013: Nebraska
Several buildings are damaged October 5, 2013 in Wayne, Neb., after a deadly storm system buried parts of Wyoming and South Dakota in heavy, wet snow. damage. Some of the greatest tornado damage occurred in Wayne, a town of 9,600.
AP Photo/Dave Weaver
May 4, 2003: Missouri
Steve Jones lifts his grandfather’s headstone into place at Stockton City Cemetery in Stockton, Missouri, after most of the headstones and nearly all of the trees in the cemetery were toppled by a May 4, 2003 tornado that killed five people.
AP Photo/John S. Stewart
June 11, 2008: Iowa
The remains of a ranger’s house can be seen after a tornado ripped through the Little Sioux Scout Ranch in remote Loess Hills, Iowa on June 11, 2008. The EF3 tornado killed four people.
AP Photo/Loren Sawyer – Onawa Watchman
July 8, 2014: Upstate New York
People sort through debris from a destroyed home after a storm July 8, 2014, in Smithfield, NY The National Weather Service has confirmed a tornado destroyed homes in upstate New York where four people were killed.
AP Photo/Mike Groll
December 10-11, 2021: Kentucky, Tennessee, Ohio Valley, Southern United States
A toppled tree lies in front of a home damaged by a tornado on December 11, 2021, in Mayfield, Ky. On December 10 and 11, violent and rare December tornadoes ripped through Kentucky and several other states. The death toll in Kentucky alone from the storms is now 80. In total, the storms have killed more than 90 people in five states. The National Weather Service recorded at least 41 tornadoes on December 10 and 11, including 16 in Tennessee and eight in Kentucky. According to the National Oceanic and Atmospheric Administration, eight states — Kentucky, Arkansas, Tennessee, Missouri, Illinois, Georgia, Ohio and Indiana — have reported tornadoes.
AP Photo/Mark Humphrey
“Weather Guys” Steve Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison.
