Warning polygon
Definition
- Related pages
- 3
- Last revised
- 23 August 2026
A warning polygon is the shape a forecast office draws around the storm it is warning for: a few straight sides enclosing where the storm is and where the forecaster expects it to go before the warning expires. The Weather Service moved to storm-based warnings so a warning covers the storm rather than every county it touches; the polygon is the unit of that system. Each one is published with the warning's issue and expiry times and, for most years of the record, the hail size and wind speed the forecaster tagged it with.
The polygon answers one question about a property, which is whether the property was inside it. That is a matter of geometry, not distance: an address is contained or it is not, and an address just outside a polygon was not warned, however close it stood. Containment is a real statement, because the office judged the storm would cross that ground, but it is about the forecaster's expectation and the storm's likely path, not about what fell at any point inside. A polygon is also a forecast of movement, so its far end may cover ground the storm weakened before reaching.
The product searches polygons by containment alone, never by radius, and it does not draw a hail swath from a tagged size, because a tag is what was expected. A polygon that contained an address is filed as an official warning, an independent kind of evidence beside what spotters reported and what radar detected, and it carries no distance because there is none to carry.
In the report
How the document prints it
In the report a polygon that contained the address appears as a row in the record table under the family it was tagged for, with the date and time it was issued, its tagged hail and wind where given, and its source, marked as measured because an office issued it; the distance column is blank for it, since containment has no distance. It is classed as contributing evidence, between a measurement at the place and a report some miles away, and its citation under Sources and method states that only polygons geometrically containing the address were searched. Polygons that passed nearby without containing the address are not in the document.
From the record
Official warnings in the record
- Independent warning sources
- 1
- Searched nationally
- 0
- Settled record from
- Fills when an address is run
- All independent sources
- 9
The record draws official warnings from one independent source, searched around each address when its report is run. Each is searched by containment: a polygon either held the address or it did not, and only the ones that did reach a report.
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
Severe thunderstorm warning
An official National Weather Service warning that a storm meeting the severe criteria for hail or wind is occurring or imminent inside a drawn area.
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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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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.
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.