Weather radar is vital for detecting and monitoring the movement and development of severe storms. Twenty-five years ago, when the Nation’s experienced its worst tornado outbreak April 3-4, 1974, National Weather Service (NWS) forecasters could see only green blobs on their radar scopes and relied on visual confirmation to issue tornado warnings. Thanks to a modernization program and an explosive growth in technology, today’s NWS has significantly advanced its radar capabilities.

Before the modernization started in the late 1980s, the NWS depended on 1950s and 1970s radar technology to operate network and local warning radars that monitored weather systems. The radar units in the national network were obsolete and difficult to service. They were so old that some of the parts were no longer manufactured.

Today, NWS forecasters detect the severe weather events that threaten life and property using Doppler weather surveillance radars (Model WSR-88D). The WSR-88D (also known as NEXRAD) observes the presence and calculates the speed and direction of severe weather elements such as tornados and violent thunderstorms. NEXRAD also provides quantitative area precipitation measurements, important in hydrologic forecasting of potential flooding. The severe weather and motion detection capabilities offered by NEXRAD increase the accuracy and timeliness of NWS warning services.


The WSR-88D uses Doppler radar technology to:

How Doppler Radar Sees Into the Future

Radar detects the presence and location of an object by bouncing an electromagnetic signal off of it and measuring the time it takes for the signal to return. This measurement is used to determine the distance and direction of the object from the radar. In the case of radar meteorology, the "objects" being measured are the particles of water, ice or dust in the atmosphere. Doppler radars take additional advantage of the fact that radar signals reflected from a moving object undergo a change in frequency related to the speed of the object traveling to or away from the radar antenna.

Therefore, using Doppler technology, the WSR-88D calculates both the speed and direction of motion of severe storms. By providing data on the wind patterns within developing storms, the WSR-88D identifies the conditions leading to severe weather. A developing tornado, for example, can be detected forming miles above the earth before it reaches the ground. This means earlier detection of the precursors to tornadoes, as well as data on the direction and speed of tornadoes once they form.


A Tri-Agency Approach

In cooperative effort with the Department of Defense and the Federal Aviation Administration, the NWS has deployed 164 radars across the country. Through an integrated network spanning the entire United States and its island territories, from Guam to Puerto Rico, the WSR-88D dramatically enhances the NWS’ ability to safeguard life, property and commerce.

For even greater detail regarding the WSR-88D, these pages will be helpful WSR-88D

NEXRAD Operational Support Facility Home Page

[ NWS Modernization Home Page ]

Maintained by the Office of Meteorology, NWS
Last modified  05/09/00.
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