A term of the record

NEXRAD

Next Generation Weather Radar. The national network of Doppler weather radars operated by NOAA and its partners, from which every radar-based figure in the record is derived.

Definition

Related pages: 5
Last revised: 23 August 2026

NEXRAD is the network of Doppler weather radars that covers the United States, operated jointly by the National Weather Service, the Federal Aviation Administration and the Air Force. Each radar sweeps the sky around it at a series of tilts every few minutes and records how much of its signal each volume of air returns, how fast that volume is moving toward or away from it, and, since the dual-polarisation upgrade, something of the shape of what reflects. Every radar image, every hail signature and every gridded radar analysis in the record begins as one of those sweeps.

A radar does not see hail. It sees reflectivity, and reflectivity is ambiguous: large stones, heavy rain and wet hail all return strongly. The radar also sees at height. The beam leaves the dish level and the earth curves away beneath it, so at a distance the lowest tilt passes far above the ground and what it records is the storm's middle, not what reached a roof. Algorithms turn the sweeps into detections and estimates of hail; only people and instruments measure it on the ground.

The product therefore treats radar as a family of evidence with two members. A radar detection, a signature an algorithm flagged in a single radar's sweep at a time and a place, is filed as an observation by an instrument. A radar-derived size, computed for every cell of a national grid, is filed as an analysis: detected, not measured, drawn with a hollow mark and never presented beside a ground measurement as though it were one.

In the report

How the document prints it

The report never prints the word on its own as a source; it prints the products derived from the network, each under its own citation. A radar detection appears in the record table as a row marked as measured, with its time and its distance and bearing from the address. A radar-derived size appears as a gridded analysis, qualified as analyzed wherever it is printed and drawn with the hollow mark, and the hail swath on the storm map is traced from it with a dashed edge, because no one stood at that line. The citation for each says which radar product it is and what it can and cannot establish.

The terms this page uses and the guides that go further. Each is shown against its own example from the record.

Term Radar detection
A hail, rotation or tornado signature an algorithm flagged in one radar's sweep at a recorded time and place, logged as an instrument's observation.
Term MESH
A radar algorithm's estimate of the largest hail a storm could have produced over a point: an analysis, detected and not measured, never a measurement.
Term Hail swath
The area a storm is estimated to have dropped hail of a given size over, drawn on a map from radar analysis or traced between ground reports.
Term ASOS
The network of automated weather stations, mostly at airports, that records the official surface observations of wind, temperature and precipitation.
Guide Measured and detected: radar hail sizes against spotter reports
The record keeps a stone measured on the ground apart from a size computed from radar, because a court will ask which is which. This guide names the kinds of evidence as the report names them, states what a radar-derived size can and cannot say, explains why a measurement is drawn as a filled mark and a detection as a hollow one, and shows how to read the two on the same day.

Sources

The primary references. Each opens on the agency's own site.

The next step

The glossary defines the word. The report is what uses it.

Everything above is definition: what the word means in the document, and what it does not. None of it says what reached one roof.

Run the address and the archive is searched at the property: the storm, the date, the measured size, the distance and bearing from the roof, and the federal record each figure came from, in a document that states its own method. About a minute.

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How this page is made

The text: Written by the editors and last revised 23 August 2026. It explains the record and how the report reads it; it contains no figure of its own.
The example: The archive holds nothing this page could show yet, so no example is printed. One appears, computed rather than written, as soon as the record holds a relevant day.
Measured and detected: A report from a person or an instrument is measured. A radar-derived size is detected, not measured, and is marked as such, here and in every document we issue. The two are never added together.
What this is not: A definition of a word the report uses. It is not a report on any property, and it states no opinion about one. The coverage page states what the record holds, by kind and by year.

About this record

Everything here is reproduced from public federal and volunteer weather records, as the agencies and observer networks that publish them released it. Titan Weather compiles the record; it does not observe the weather, and it is not affiliated with any source it cites.

No archive holds everything. Storms cross places where nobody is standing, instruments and spotters cover some areas better than others, sources revise their records, and recent reports can take weeks to arrive and settle. Where this page shows nothing, nothing was found in the sources searched, within the period and area it states. That is not a finding that no weather occurred.

These pages describe the public record near a place or on a date. They do not establish what reached any particular property, and nothing here is insurance, legal or engineering advice.