Overview
On 26 June 2026, the Hadley Centre Central England Temperature (HadCET) series recorded a daily mean of 26.5°C — the highest ever measured for any June day in a dataset spanning 254 years. These charts place that heatwave in context: each dot represents one day in June, from 01 June 1772 to 30 June 2026, for daily mean, maximum, and minimum temperature. Only 4 of those 7,650 June days have ever exceeded 24°C as a daily mean — all four in June 2026. The LOESS trend lines trace the century-scale pattern across the full series.
Methodology
Data was downloaded directly from the Met Office HadCET dataset
(meantemp_daily_totals.txt), the longest instrumental temperature record in the world.
All June readings (days 1–30, years 1772–2026) were extracted using Python. A LOESS smooth was fitted
to the 7,900 data points to show the underlying trend. The interactive chart was built in JavaScript
using D3.js, with Delaunay triangulation for efficient nearest-point detection on hover and click.
Findings
- Daily mean: All 4 June days above 24°C in 254 years were in June 2026 (23–26 June: 24.1, 24.3, 25.0, 26.5°C). The series record is 26 June 2026 at 26.5°C.
- Daily maximum: 4 of the 5 hottest June days on record were in June 2026. The series record is 26 June 2026 at 32.8°C, exceeding the 1976 heatwave peak of 30.3°C.
- Daily minimum: The warmest June night on record was 26 June 2026 at 20.1°C — 2.8°C above the previous record from 22 June 1941 (17.3°C).
- The coldest recorded June daily mean in the series: 19 June 1795 at 7.3°C.
Takeaways
Open climate data — and especially a dataset spanning over two centuries — makes it possible to contextualise a single extreme reading immediately and precisely. The HadCET series is public, machine-readable, and updated in near real-time by the Met Office. A record like 26 May 2026 can be verified, contextualised, and published within hours of its occurrence. That is what open data enables.