# KNMI daily weather data

Daily values from over fifty weather stations: temperature, rainfall, sunshine and wind. The De Bilt series starts in 1901.

- Publisher: Koninklijk Nederlands Meteorologisch Instituut
- Area: Netherlands · Finest detail: weather station
- Period: 1901 – 2026 · Refreshed: daily
- Access: Open · Licence: CC BY 4.0
- Join keys: stationsnummer, datum
- Status: bad
- URL: https://www.knmi.nl/nederland-nu/klimatologie/daggegevens

## What can you do with it?
- **Was this summer exceptional?.** Compare this summer's mean with all summers since 1901 and see where it ranks.
- **Count the tropical days.** A tropical day has a maximum of 30 °C or more (variable TX). Count them per year.
- **Build your own warming stripes.** One stripe per year, coloured by deviation from 1901–1930. The chart on this page is exactly that.

## How to process it
1. **Choose station and variables.** De Bilt is 260. Variables: TG (mean), TX (max), TN (min), RH (rain), SQ (sunshine).
2. **Fetch daily values.** One POST request with start and end date. JSON is easiest.
   `curl -d "stns=260&vars=TG:TX&start=19010101&end=20251231&fmt=json" https://www.daggegevens.knmi.nl/klimatologie/daggegevens`
3. **Divide by ten.** Temperature and rain are in tenths. -1 for rain means less than 0.05 mm.
4. **Average per year or season.** Drop or flag years with missing days, or the average will be skewed.

## Interesting combinations
- More nuisance in warm weather? → [politie-overlast](https://www.opendataindex.nl/en/bron/politie-overlast.md) via datum (maand). Compare monthly temperature with reports and with the same month in cooler years.
- Is air worse in still weather? → [luchtmeetnet](https://www.opendataindex.nl/en/bron/luchtmeetnet.md) via datum en uur. Wind (FG) and hourly air quality together show how much the weather determines.

## Similar sources
- [era5](https://www.opendataindex.nl/en/bron/era5.md): A grid over all of Europe, including where no station stands, but coarser.
- [KNMI Data Platform](https://dataplatform.knmi.nl): Hourly data, radar and models. Requires a free API key.

## What to watch out for
- **Raw measurements, not a trend series.** Changes in instruments and surroundings are part of this series. KNMI also publishes a homogenised De Bilt series; use that when comparing periods before 1951.
- **One station is not the whole country.** On the coast summers are cooler and winters milder than in De Bilt. Pick the station that fits your question.
- **Values in tenths.** TG = 115 means 11.5 °C. Rainfall is in tenths of a millimetre.
- **Recent days are provisional.** The most recent days may still be corrected after validation.

## How to fetch it
```bash
curl -d "stns=260&vars=TG&start=20250101&end=20251231&fmt=json" \
  https://www.daggegevens.knmi.nl/klimatologie/daggegevens
```