Our Data & Methodology
Every number on this site is computed, not copied. This page explains exactly where each figure comes from, so you can judge - and cite - our data with confidence.
Climate averages (the historical layer)
Each city page shows monthly climate normals built from ten full years (2015–2024) of daily weather history:
- Source: the ERA5 reanalysis dataset, accessed through the Open-Meteo archive API - the same data family used in climate research.
- Resolution: daily highs, lows, precipitation, snowfall, sunshine and humidity for each city's exact coordinates.
- Aggregation: roughly 3,650 daily records per city are averaged into monthly normals; record values are the extremes within the same window.
- Climate types follow a simplified Köppen classification computed from those normals.
Because the window is fixed (2015–2024), the averages are stable and comparable across all 493 cities - they don't drift with each site update.
Live conditions and forecasts
- Source: WeatherAPI.com (current conditions, 48-hour hourly, 14-day daily, air quality, alerts, astronomy).
- Refresh: each city's bundle is cached for about 30 minutes, then refreshed on the next visit.
- Freshness labels: every live page shows when its data was last updated; if the upstream feed is briefly unavailable, we show the last good observation and say so.
Rankings
The hottest and coldest lists compare the most recent cached observation for every covered city - a live snapshot, not a climate ranking. No modeled or interpolated values are mixed in.
Editorial content
City and country descriptions are generated from each location's own climate figures - the hottest month named in a city's text is that city's actual hottest month in the data. Guides are written and reviewed by our editorial team against the primary sources listed at the bottom of each guide (NWS, USDA, FDA, EPA and peers), with a visible last-reviewed date.
Corrections
Spotted something off? Tell us - corrections ship quickly, and the fixed page updates its modification date.