Data sources

Hailstory derives its figures from public data. NOAA does not endorse Hailstory or its figures.

Radar hail

Hail estimates come from the Multi-Radar Multi-Sensor (MRMS) maximum estimated size of hail, known as MESH, published by NOAA through the NOAA Open Data Dissemination program on AWS. Hailstory reads one daily file for each storm day, which runs from 12:00 to 12:00 UTC, from October 2020 onward.

The sizes on this site are not the original NOAA values. Hailstory changes them before storing them: sizes are rounded, speckle is removed, and only values of 12.7 mm (half an inch) or more are kept. When a result is looked up, storms in the neighbouring grid cells also count, because hail drifts as it falls. The grid is about 1 km. These steps are why Hailstory figures should not be read as NOAA data.

Ground reports and tornado tracks

Hail, wind and tornado reports come from the Storm Prediction Center (SPC) severe weather database, which covers 1950 through 2025, and from the SPC daily storm report files for 2026 onward. Preliminary daily reports can change when SPC reviews them.

Places and addresses

ZIP code and county centers and land areas come from the US Census Bureau Gazetteer files. Addresses are turned into coordinates by the US Census geocoder. When it finds nothing, a single address typed on the home page can fall back to Photon, run by Komoot, which uses OpenStreetMap data.

Maps

About these figures

Hailstory is independent. It is not affiliated with or endorsed by NOAA, the National Weather Service, the Storm Prediction Center, or the Census Bureau. Radar sizes are estimates and are not proof of damage. The accuracy page shows how they compare with ground reports.