Cooperative observer
Definition
- Related pages
- 4
- Last revised
- 23 August 2026
A cooperative observer is a volunteer who keeps a weather station at a fixed site, usually a home, a farm or a utility yard, with instruments the National Weather Service issues and inspects, and who records temperature, precipitation and related readings once a day, every day. The programme is as old as the Weather Service itself, created by the same act, and its stations are the backbone of the climate record for most of the country. A separate volunteer network measures rain, snow and hail with a standard gauge and a hail pad, and its observers are trained to report hail by stone size and duration.
An observer differs from a spotter in what is asked of them. A spotter reports an event while it happens, from wherever they are; an observer measures at a site, on a schedule, with a calibrated instrument, whether or not anything happened. An observer's hail report is therefore made at a known point with a known method, and the site has a history a reader can check against. It is also bounded by the site: it says what fell in that yard.
The fixed site is the observer's limit as well as the strength: a gauge reads what fell on one yard, and a storm that crossed the county a mile north is absent from it, which is why the record prints the site's distance from the address. An observer network and a forecast office's reports are counted as separate independent sources, because they reach the record by different routes.
In the report
How the document prints it
In the report an observer's hail measurement is a row in the record table under hail, with the date, the size, the distance and bearing from the address and the source that carried it, marked as measured. The citation for that source under Sources and method describes the network and states the radius it was searched at. In the findings it is one kind of evidence, a ground observation, and a day carried by an observer and by a forecast office's reports is still one kind, however many sources of that kind agree.
From the record
Ground observations in the record
- Independent ground sources
- 6
- Searched nationally
- 4
- Settled record from
- 1996
- All independent sources
- 9
The record draws ground observations from 6 independent sources, 4 of them searched nationally, with the earliest settled national coverage beginning in 1996. Observer networks and forecast offices are counted among them separately, because their reports reach the record by different routes.
Measured Detected, not measured
Related
The terms this page uses and the guides that go further. Each is shown against its own example from the record.
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Term
Trained spotter
A volunteer who has completed National Weather Service spotter training and reports severe weather to a forecast office by an agreed method.
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Term
Spotter report
An eyewitness report of hail, wind or a tornado made by a person at the scene and passed to a forecast office, with the place and time attached.
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Term
Independent source
A record-keeping route by which a storm reached the archive, counted once however many rows it produced, so that agreement between routes can be measured.
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Guide
How far away a hail report can be and still count
A hail report is a point: where a person stood, or where a radar placed a signature. A property is another point. The distance between them is the first thing a reader checks and the first thing a reader misreads. This guide states what a distance establishes, how the report bands it, and why a record filed to a county cannot be measured from at all.
Sources
The primary references. Each opens on the agency's own site.
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.
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
- Drawn from the archive when the page was compiled, 24 August 2026, and rebuilt daily as the record deepens. Every figure in the panel marked From the record is computed, not written, and links to the page it came from.
- 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.