NEXRAD (Next-Generation Radar) is the network of about 160 high-powered Doppler radar stations operated by the National Weather Service that supplies the radar data behind nearly every rain map, weather app, and severe storm warning in the United States.
A Nationwide Web of Radar Towers
Each NEXRAD station, officially designated WSR-88D, sits inside the large white dome you may have spotted near an airport or Weather Service office. The stations are spaced across the country so their coverage areas overlap, giving forecasters a near-continuous view of precipitation from coast to coast, though coverage does thin out over parts of the mountain West and offshore.
What Each Station Actually Sends Out
Every NEXRAD site continuously sweeps the sky at multiple angles, sending back both reflectivity data (how heavy precipitation is) and velocity data (wind direction and rotation), the same two data types described in our guide to how Doppler radar works. That raw data feeds directly into the National Weather Service’s warning system and is also what most third-party weather apps and websites display, including a live rain radar map.
Why Some Areas See Better Radar Coverage Than Others
Because the radar beam curves slightly and rises with distance from each tower, locations near a NEXRAD station typically get a clearer, lower-altitude view of precipitation than locations sitting between two distant stations. Mountainous terrain can block the beam entirely in some valleys. Our article on radar blind spots goes into more detail on where and why coverage gaps happen.
The Dual-Polarization Upgrade
Between 2011 and 2013 the entire NEXRAD network was upgraded to dual-polarization, and it was the most significant improvement in the system’s history. Before the upgrade each radar sent out pulses oscillating in one plane only. Afterwards they transmit both horizontally and vertically.
That sounds like a technicality but it changed what radar can identify. Comparing the two returns reveals the shape of what the beam is hitting. Raindrops flatten as they fall, so they return wider horizontally. Hailstones tumble and are roughly spherical. Snowflakes are irregular. Insects, birds and windblown debris look different again.
The practical result is that forecasters can now distinguish rain from hail from snow from non-weather clutter, estimate hail size, and detect the debris lofted by a tornado already on the ground — a signature that confirms a tornado is doing damage even when no one has seen it.
Where Coverage Runs Thin
About 160 stations sounds comprehensive, and across the eastern two-thirds of the country it broadly is. But NEXRAD coverage has real gaps, and they follow a pattern.
- The mountain West. Terrain blocks beams and stations are further apart. Parts of the Great Basin and the northern Rockies have poor low-level coverage.
- Beam height at range. Because the Earth curves, the beam is around 3,000 metres up at 150 km from the station. Shallow low-level precipitation between distant stations is simply missed.
- Offshore. Coverage extends only so far out to sea, which is why approaching tropical systems are tracked by satellite until they close on the coast.
- Alaska. Coverage is sparse relative to the land area.
How NEXRAD Data Reaches Your Phone
Raw NEXRAD output is public. The National Weather Service distributes it in two forms: Level II, which is the full-resolution raw data, and Level III, which is processed products derived from it.
Nearly every consumer weather app builds on this. They ingest the public feed, apply their own colour scale and smoothing, sometimes blend in satellite estimates for areas outside coverage, and present the result. This is why different apps can look quite different while showing identical underlying weather — and why they all tend to fail in the same places, because they share the same gaps.
Frequently Asked Questions
What is NEXRAD?
NEXRAD, short for Next-Generation Radar, is the United States network of about 160 WSR-88D Doppler weather radar stations operated by the National Weather Service. It supplies the radar data behind most American weather apps, rain maps and severe storm warnings.
How many NEXRAD radar stations are there?
Approximately 160 across the United States and its territories, positioned so coverage areas overlap, though gaps remain in the mountain West, offshore and across Alaska.
What is dual-polarization radar?
An upgrade completed across the NEXRAD network by 2013 in which radars transmit pulses both horizontally and vertically instead of in one plane only. Comparing the returns reveals the shape of what the beam hits, allowing forecasters to distinguish rain from hail from snow, estimate hail size and detect tornado debris.
Is NEXRAD data free to use?
Yes. The National Weather Service distributes NEXRAD data publicly as Level II raw data and Level III processed products, which is why so many commercial and free weather apps can display American radar.
Why does NEXRAD miss rain in some areas?
Mainly because of beam height and terrain. The Earth curves away from the straight radar beam, so at long range the beam scans thousands of metres up and misses shallow low-level precipitation. Mountains also block beams outright, creating shadows behind high ground.
Does NEXRAD cover the ocean?
Only near the coast, within roughly 150 to 250 km of a station. Tropical systems approaching from open ocean are tracked by satellite and reconnaissance aircraft until they come within radar range.
In Conclusion
The next time you check a rain map, you’re looking at data gathered by one of roughly 160 government-operated radar towers scanning the sky around the clock. NEXRAD is the quiet infrastructure behind almost every weather warning you’ve ever received.
