Independent source
Definition
- Related pages
- 5
- Last revised
- 23 August 2026
An independent source is one of the routes by which a storm enters the record: a forecast office's reviewed entries, the national preliminary log, a volunteer observer network, the radar inventory, the warning archive, the survey toolkit. Each is kept by a different body, on a different schedule, from a different kind of observation, and each is counted once for a day no matter how many rows of it there are. Three feeds that relay one spotter's report are one source. A spotter, a radar signature and a warning for the same storm are three.
The count is the product's unit of corroboration, and it answers the question a reader puts to any single report, which is whether anyone else recorded the same thing. A day carried by one source is a report; a day carried by several is a storm that independent record-keepers agree happened. The count is deliberately modest. It does not say the sources agree on size or on place, only that each holds something for the day near the place; and it does not grow when the same report is copied, because a copy is not a witness.
Independence is also the rule by which the report grades confidence, with one refinement: there it counts kinds of evidence rather than sources, so two ground-observation sources are one kind and a ground observation beside a radar detection is two. A finding that rests on an analysis alone is graded as modelled only, however many rows support it, because an estimate cannot corroborate itself.
In the report
How the document prints it
In the report the findings section grades each family of evidence by how many independent kinds support it: strongly corroborated for three or more with at least one measured, corroborated for two, single source for one measured kind, and modelled only where nothing was measured at all. Each finding prints the count of days, records and kinds beneath its statement, and the reading guide at the back defines the grades. In the record table every row names its source, so a reader can count the routes for any day themselves, and Sources and method lists each source once with what it can establish.
From the record
Storm days in the last year by how many sources carried them
- Hail days in the window
- 250
- Carried by one source
- 25
- Carried by two
- 87
- Carried by three or more
- 138
Of the 250 days with hail on record nationally since 24 August 2025, 25 were carried by a single source, 87 by two, and 138 by three or more. The last group is the one in which independent record-keepers agree a storm happened.
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
Storm day
A calendar date on which hail, wind or tornado reports were filed, counted as one day however many reports it carries.
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Term
SPC storm report
A preliminary hail, wind or tornado report collected nationally by the Storm Prediction Center from forecast offices on the day it was filed.
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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.
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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.
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Guide
How to read a hail report: what each figure means
A hail report is a list of records with figures attached, and every figure on it came from somewhere in particular. This guide walks the document in the order a reader takes it: the date and the window searched, a measured size beside a detected one, the distance and bearing from the address, the count of independent sources, and the line at the end that says what the report does not claim.
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.