Data Sources & Methodology
Every figure on Weather On This Day traces back to an official government weather record. This page documents the datasets we use, how our analyses are computed, and how to cite our work.
Primary Datasets
| Dataset | Provider | Coverage | Used for |
|---|---|---|---|
| GHCN-Daily (Global Historical Climatology Network) | NOAA NCEI | 1970–present · 14,000+ US stations · 139M+ daily observations | Daily temperature, precipitation and snowfall history; records; historical averages |
| SPC Tornado Database | NOAA Storm Prediction Center | 1950–present · every recorded US tornado | Tornado pages: EF ratings, paths, fatalities, outbreak analyses |
| HURDAT2 Atlantic Best Track | NOAA National Hurricane Center | 1851–present · every Atlantic tropical cyclone | Hurricane season statistics, landfall counts, ENSO–hurricane analyses |
| Oceanic Niño Index (ONI) | NOAA Climate Prediction Center | 1950–present · 3-month running ERSST.v5 anomalies, Niño 3.4 region | El Niño / La Niña season classification (El Niño = ONI ≥ +0.5°C) |
| Billion-Dollar Weather Disasters | NOAA NCEI | 1980–present | Damage estimates in historical disaster rankings |
| UK Climate Extremes | UK Met Office | National records for England, Wales, Scotland, Northern Ireland | UK and European record pages |
How Our Analyses Are Computed
Historical averages for a given date and location are computed from a rolling window of daily GHCN-Daily observations at the nearest reporting stations, typically 25 years of records.
Records (“hottest ever”, “coldest ever”) reflect the full station history available, and each record is presented with its date and recording station so it can be independently verified against the upstream dataset.
ENSO classifications follow the NOAA CPC convention: a season counts as El Niño when the Oceanic Niño Index averaged ≥+0.5°C over the relevant months, with strength tiers at 0.5, 1.0, 1.5 and 2.0°C. Cross-dataset analyses (for example, storm counts by ENSO phase) state the season count and years included alongside the averages.
Provisional figures from very recent events are labeled as provisional until ratified by the source agency (for example, Met Office ratification of new UK records), and updated once confirmed.
Update Cadence
Editorial analyses on /trends carry a visible published date and an updated date when figures change. Event-driven pages (active seasons, live outbreak coverage) are refreshed as new agency data is released. Historical record pages change only when a record is broken or a source agency revises its data.
How to Cite Weather On This Day
Our analyses are free to reference with attribution. Suggested formats:
“According to Weather On This Day’s analysis of NOAA records, …” (weatheronthisday.com)
Weather data from Weather On This Day (weatheronthisday.com), sourced from NOAA Climate Data Online.
Please link to the specific analysis page you reference so readers can see the full table and methodology behind the figure.