Typical Weather

Why not just the climate average?

If you plan a wedding, a holiday or an event months ahead, a forecast is no help: it reaches two weeks at most. What you can do is look at what the weather is usually like on that day.

Meteorologists use the average over thirty years for that; most weather services currently use 1991 to 2020. Such an average lags behind: its middle lies more than twenty years in the past, and it has become noticeably warmer since. Taking only the last ten years is no answer either, as a single heatwave or wet summer then pulls the average all over the place.

Three periods instead of one average

Typical Weather therefore cuts history into three periods that do not overlap: the last ten years, the thirty years before, and everything older. In each period, every day of the year gets the average of the daytime highs from a week before to a week after. The last ten years count for 45 percent, the thirty years before for 35 percent and the older records for 20 percent.

That way the recent past weighs most, without one outlier deciding everything. And side by side, the three periods show how fast each place is warming: in London in June, Amsterdam in June or any other city.

Weather stations instead of models

The measurements come from GHCN-Daily by the US NOAA: daily observations from weather stations around the world, often going back more than a century. The record of De Bilt in the Netherlands starts in 1901. Each region uses one station with a long, reliable record.

For recent years, ERA5 was used at first: a reanalysis, a weather model that combines all observations into a grid over the whole earth. Put next to the stations, ERA5 turned out 0.7 to 1.1 °C cooler on average, and up to four or five degrees in mountains and on islands, because a grid cell some thirty kilometres wide averages a mountain, a valley and a coast into one number. So all periods now come from the station itself wherever possible. Only where a station misses recent years is ERA5 still used, corrected by the difference between station and model in the years both existed. For Amsterdam on 12 June, that moved the typical daytime high from 19.3 to 20.2 °C.

Between the stations

Not every place has a weather station nearby. For a place between stations, Typical Weather averages the three nearest within 300 kilometres, a station twice as close counting four times as much. Tested by leaving out one station at a time and predicting it from the others: with the nearest station alone the error is 1.8 °C on average, with the weighted average 1.5 °C. For places that really lie between two stations, the error drops from 1.8 to 1.0 °C.

What you find on the site

For any place and date, the typical daytime high, with the days around it. Per day the three periods apart, the night-time low, the range the daytime high falls in on eight days out of ten, the warmest and coldest day on record and how fast that time of year is warming.

Each country has an overview, such as the average temperature by month for every UK city, and you can compare cities, for example Berlin in July with Madrid in July. The site is available in English, Dutch, German, Spanish, French and Portuguese.