Climate
Temperatures and rain come from daily weather-station observations for the ten most recent complete years, served by Meteostat from national weather services. For each city we take the nearest station with sufficient temperature coverage, and the nearest station within 100 km that records precipitation in every month; both are named with their distance from the city centre in the source line of every page. From the daily values we compute, for each calendar month: the mean of daily highs and lows; total precipitation; the number of days with at least 1 mm of rain; the 10th and 90th percentiles of daily highs; the number of days above 30 °C and nights at or below 0 °C; days with snow cover of at least 1 cm where the station records snow depth; and the mean high and low for the first, middle and last third of the month. Sunshine hours are shown only where the station records them.
Paris uses the ERA5 reanalysis served by the Open-Meteo Historical Weather API at the city-centre coordinates. Reanalysis agrees with station normals on temperature to within about 1 °C but counts more light-rain days than a city-centre station, because it averages over a grid cell. Airport stations, which most cities use, can run one or two degrees cooler at night than the dense centre.
Daylight
Sunrise and sunset are computed with the NOAA solar equations for the city coordinates and time zone, including daylight-saving changes. Accuracy is within about one minute.
Crowds
Where official monthly hotel-arrival statistics exist, the crowd index is each month's arrivals divided by the monthly average of the same year, using the most recent complete year published as a monthly series. The four-step scale is: low below 0.90, shoulder 0.90 to 0.99, high 1.00 to 1.07, peak 1.08 and above. Hotel arrivals include business travellers and exclude short-term rentals and day visitors, so the index describes how full the city is, not only how many tourists are at the sights. Where no monthly series is available, the scale is an editorial estimate and the page says so.
School holidays, public holidays, events
School-holiday dates come from the national or regional authority for each source market and are linked on every page. Public holidays come from the Nager.Date API or are computed from the official holiday rules. Dated events are listed only with an organiser or press source and a link; expected dates that the organiser has not yet confirmed are marked as such. Recurring events without a published date for the coming year are shown with their usual timing.
Verdicts and FAQs
The "Excellent / Good / Mixed / Off-season" label is a fixed formula: points for daytime temperature (mild or warm scores highest), rain days and crowd level. The FAQ answers are generated from the same data, so they change when the data changes. The one section written by hand is "What the numbers don't tell you", which is checked against the sources listed in its city's data file.
Updates and corrections
Pages are rebuilt when the data changes; the date at the top of each page is the last build. If you find an error, write to the editors with the page URL and the source that contradicts it.