Definition
A network of high-resolution Doppler weather radars operated jointly by the National Weather Service, the FAA, and the Department of Defense, which detects precipitation and atmospheric movement and produces the radar weather imagery widely used in aviation weather products. Each site transmits a radar beam, measures the energy reflected back from precipitation, and uses Doppler shift to determine the speed and direction of that precipitation, allowing the system to display intensity, coverage, and movement of weather across the United States.
Plain English
NEXRAD is the country's main weather radar network. It bounces radar signals off rain, snow, and storms to show where the weather is, how strong it is, and which way it's moving. The colored radar pictures pilots see in cockpit weather displays and on briefing websites come from this system.
Context Anchor
Seen on multi-function displays and other cockpit weather displays when reviewing datalink weather during flight planning or while in flight.
Derivation
Doppler refers to the Doppler effect, named after Austrian physicist Christian Doppler, which describes how the frequency of a returning signal shifts when the object reflecting it is moving. That shift is what lets NEXRAD measure not just where precipitation is, but how fast it is moving toward or away from the radar.
Why Pilots Care
Gives pilots an immediate view of hazardous weather so they can plan routes that avoid thunderstorms, heavy rain, and areas of strong winds.
Analogy
NEXRAD on a cockpit display is like checking a traffic map that was updated a few minutes ago. It is very useful for seeing the big picture, but it may not show the exact situation at this instant.
Intuition Check
Do not assume NEXRAD is live onboard radar. It is ground radar information that has been processed and sent to the aircraft, so the displayed weather may lag behind the actual weather.
Example Sentence 1
The pilot checked the NEXRAD image during preflight and saw a line of strong returns moving across the planned route.
Example Sentence 2
With NEXRAD data available, the crew adjusted their altitude to stay clear of the heaviest precipitation cells.