Data sources and methodology

What records do we use?

We use preserved ERA5 reanalysis data retrieved from the Open-Meteo Archive API, covering 100 cities over 2010–2025. This is gridded data combining observations and models, rather than a dataset consisting only of direct weather station observations.

How do we count?

The daily thresholds are maximum temperature ≥ 33°C, precipitation ≥ 30mm, maximum wind gust ≥ 70km/h, and minimum temperature ≤ -10°C. A year counts once if at least one day in the period meets any threshold. Overlapping conditions do not count twice in the overall total.

The weekly table compares 52 seven-day intervals starting on January 1. February 29 and December 31 are excluded from weekly aggregation. The full period covers 16 years (2010–2025), and the recent period covers 8 years (2018–2025). Date-range exploration uses the actual calendar. Ranges crossing the year boundary or including leap day can have different numbers of valid years. Always read the denominator shown in the app.

The historical share is the number of years meeting a threshold divided by the number of years compared. Counts for individual weather conditions use all valid years and can overlap. Do not add weekly counts to obtain annual event totals. Missing records are shown as unavailable, never as zero.

How are the records maintained?

We apply the same rules to preserved source data and check whether the data has changed.

What can these records tell us?

Historical statistics are not forecasts or probabilities that guarantee weather on your travel dates. Gridded data cannot capture every elevation, coastal or microclimate difference within a city. The gust threshold does not directly classify typhoons, and these four thresholds cannot describe every aspect of travel comfort. The current MVP operates within the non-commercial scope of Open-Meteo’s free plan.