HailEvidence → methodology

Methodology & sources

Everything on this site and in every report is derived from two cited federal sources. Nothing is modeled, estimated, or proprietary — which is the point: an adjuster can verify every line against the official record.

Sources

1. NOAA NCEI Storm Events Database — the official record

The official National Weather Service storm record, 1950–present. Yearly files are re-compiled by NCEI; this site stamps the compile vintage it serves. We load the yearly bulk files (https://www.ncei.noaa.gov/pub/data/swdi/stormevents/csvfiles/) for hail, thunderstorm wind, high wind, strong wind, and tornado events. NCEI re-compiles yearly files; we re-pull the current and prior year monthly and refresh the archive annually, replacing whole years so amended records replace stale ones. Every page and report stamps the compile vintage it was generated from. Currently on file: 1,189,226 events, vintage c20260527, with final records through 2026-02-28.

2. NOAA SPC daily storm reports — the same-day feed

Same-day local storm reports relayed by NWS offices; preliminary and later reconciled into the Storm Events database. All times UTC. We ingest the daily hail/wind/tornado CSVs nightly (re-fetching the prior three days, which SPC amends). These reports are preliminary: NWS later reconciles them into Storm Events. To avoid double-counting, reports and pages use Storm Events up to its coverage horizon and SPC only after it — and every row is labeled Storm Events · final or SPC · preliminary. Currently loaded through 2026-06-11.

How the numbers are computed

Distances are great-circle miles from recorded NWS coordinates to the city centroid (city pages), ZCTA centroid (ZIP pages), or the geocoded address (reports — geocoding via the free US Census geocoder; "lat, lon" input accepted). NWS positions are reported relative to landmarks and can be approximate.
City pages count events within 10 miles of the centroid; ZIP pages within 5 miles of the ZCTA centroid (a ZIP is an area — neighboring ZIPs overlap, and we say so).
Hail sizes are as recorded (inches; SPC reports sizes in hundredths of an inch). Wind speeds in Storm Events are knots — we display mph (1 kt = 1.15078 mph) with the original value in reports. "UNK" values are shown as not recorded, never guessed.
County-level records: many pre-1996 Storm Events records carry no coordinates. In reports they appear as county-level matches with no distance — assigning one would be fabrication.
City universe comes from the US Census 2026 gazetteer (place and ZCTA centroids). Pages exist for the launch metros and every city with recorded hail nearby this season, growing nightly as storms happen.

Honest limits

NWS records are point and path observations. The absence of a nearby report does NOT prove that no hail fell at this address — it means no observation was logged nearby. A report of nearby hail documents the event; it does not by itself prove damage to a specific structure. Additionally: source records can be wrong, late, amended, or missing. We reproduce them faithfully and stamp vintages so you can check what we checked.

Corrections

Spot an error — about a storm, a place, or anything a page says? Reply to any email from us, and a human will verify against the source records and correct or remove it promptly.

Storm Events vintage c20260527 SPC loaded through 2026-06-11 last ingest 2026-06-12