The National Weather Service (NWS) has nearly completed a major modernization
program to improve the quality and reliability of its products and
services. One important key to the modernization is the new Doppler
weather surveillance radar (Model WSR-88D). The WSR-88D (also known
as NEXRAD) excels in detecting the severe weather events that threaten
life and property, from early detection of damaging winds to estimating
rainfall amounts for use in river and flood forecasting.
NEXRAD Tower
The WSR-88D uses Doppler radar technology to:
- Substantially increase tornado warning lead time.
- Improve the detection and measurement of damaging winds, severe
turbulence, wind shear and hail storms.
- Improve the forecast of the location and severity of thunderstorms.
- Increase the accuracy of identifying areas that are threatened.
- Substantially reduce the number of incorrect forecasts and false
alarms.
The WSR-88D capabilities will also:
- Increase the accuracy of rainfall estimates for flash flood warnings.
- Improve water resource management and river flood forecasts.
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 new WSR-88D can often identify
the conditions leading to severe weather. A developing tornado, for
example, can often be detected forming thousand of feet above the
earth before it reaches the ground. This can be an important tool
in the early detection of the precursors to tornadoes, as well as
data on the direction and speed of tornadoes once they form.
Tornado Depicted by NEXRAD
A Tri-agency Approach
In cooperative effort with the Department of Defense and
the Federal Aviation Administration, the NWS completed the deployment
of some 164 radars during the mid-1990s. Through an integrated network
spanning the entire United States and its island territories, from Guam
to Puerto Rico, WSR-88D has dramatically enchanced our ability to safeguard
life, property and commerce.
To learn more about radar meteorology in general...check out this [tutorial.]
www.srh.weather.gov 
