Updated: 2026-08-09
The warmest stretch on record at London's St James's Park lasted 101 consecutive days with high temperatures above 20 °C. This remarkable warm spell began on 7 June 2022 and ended on 15 September 2022, enveloping much of the British summer in persistent warmth. The 101 days represent the longest unbroken run above the 20 °C threshold in a series spanning from 1912 to 2025.
When Londoners say "summer," they are usually describing days when it is genuinely warm enough to eat outdoors, sit in the park without a jacket, or go for a long bike ride. Meteorologically, the 20 °C threshold captures this well: days with a maximum temperature above 20 °C mark the point where the British capital starts to feel decisively summery. The duration of such a warm spell is more than a statistical curiosity—it shapes energy demand, public health patterns, and the rhythm of outdoor life in the city.
In 2022, London enjoyed the longest continuous summer of the entire 114-year record. The first day above 20 °C in that run fell on 7 June 2022, and the chain of consecutive days did not break until 15 September 2022. That makes a straight run of 101 days of golden, warm or even hot weather, stretching across three months of the year. It is a striking contrast to the rest of the record, where such long uninterrupted warm periods are uncommon.
The station at London St James's Park (the Met Office site identifier 00697) has been recording temperature data since at least the beginning of the twentieth century. The earliest entry in this composite series is dated 1 January 1912, while the most recent is 31 December 2025. This spans more than a century of daily observations, enough to map out the normal rhythm of London's summer warmth with confidence.
When we look at the mean monthly maximum temperature across the year, the warmest month is July, with an average high of 22.6 °C. August follows closely at 22.3 °C; June sits at 20.8 °C. These three months are the only ones with a mean maximum above the 20 °C line, which puts the 2022 run into context: for a full 101 days to stay above that threshold, both June and September needed to start and end well within the warm range.
| Month | Mean daily maximum (°C) |
|---|---|
| January | 7.7 |
| February | 8.2 |
| March | 10.9 |
| April | 13.9 |
| May | 17.7 |
| June | 20.8 |
| July | 22.6 |
| August | 22.3 |
| September | 19.7 |
| October | 15.5 |
| November | 10.9 |
| December | 8.6 |
Autumn and spring clear the 20 °C bar on many individual days, but the monthly averages show how tenuous the warmth is outside summer. September's mean maximum is 19.7 °C, a hair below the threshold, so any late warm spell must overcome a substantial cool start or finish. October's average of 15.5 °C indicates that the warm season normally winds down well before the clocks change.
The 2022 season stands out precisely because it jumped the hurdles of a still-chilly early June and a normally fading September. Starting on 7 June and persisting until 15 September, the spell crossed the full meteorological summer and spilled into early autumn.
To give this some perspective, the monthly mean maximums suggest a core warm season of approximately three months—June, July and August—when the average daily high is already above 20 °C. A run of 101 consecutive days above that level means the warmth did not merely cover the climatological summer; it started late enough in spring to merge seamlessly into the core summer and lasted well into September. That long breathing time of warm weather is what records are made of, and it reflects the kind of persistent high-pressure pattern that occasionally locks over southern England.
For daily life, the difference between a warm spell of a few weeks and one that spans 101 days is enormous. It is the difference between one heatwave and a whole season of reliably warm air. People plan outdoor events, summer festivals and garden gatherings around this. Tourists flock to London when the weather holds. The 2022 run had all the hallmarks of a classic warm British summer, only elongated.
The record also matters for how we think about climate. The series starting in 1912 captures many warm summers: 1947, 1959, 1976, 1989, 1995, 2003 and 2018 are all remembered for strong summer warmth. Yet none of them produced a continuous run that outlasted the 101 days reached in 2022. That date range, beginning on 7 June and ending on 15 September, remains untouched at the top of the list.
Because this is an analysis of consecutive days, the break in the run matters as much as the start. To achieve 101 days, the city had no single day between 7 June and 15 September in which the maximum temperature dropped to 20 °C or below. Any cool, rainy, or overcast day would have ended the streak. That it survived the entire British summer is a testament to how unusually settled and warm the weather pattern was.
The methodology used for this series takes the daily maximum temperature at London St James's Park, begins with the first day above 20 °C and counts forward without interruption while each successive day also exceeds the threshold. The single longest such chain in the 1912–2025 series is thus the 101 days that ran from 2022-06-07 to 2022-09-15. The raw data come directly from the Met Office's integrated data archive, the MIDAS system, which holds the national weather station network's records.
It is worth repeating that the run length is what makes this an extreme event. A summer can be warm on average yet still see intermittent cooler days. What 2022 produced was an unbroken ribbon of warmth, likely to be remembered as one of the most sustained warm seasons in the capital's modern meteorological history. While the series covers many decades of weather at the park, the combination of early summer onset and late autumn extension seen in 2022 has not been matched in the available record.
London's climate is famously mild, but the 20 °C threshold is not guaranteed every day even in high summer. Cloud, rain, and cooler maritime air can pull a July day below this mark. This makes the 2022 run all the more remarkable: the city experienced 101 straight days of warmth, probably enjoying the kind of long, balmy summer that rarely visits northern Europe. The numbers are grounded entirely in the official station data, so anyone planning around London's warm season can take confidence in the pattern described here.
The contrast with monthly averages is sharp: July and August are the only months with means above 22 °C, yet September sits at 19.7 °C. For the 2022 spell to extend to 15 September, each late-summer day had to beat the climatological average. The persistence of high pressure over southern England during that period is what carried the temperature across the finish line.
The warm season in London, measured by this definition, rarely fits neatly into the calendar, but the 2022 run set a standard that will be hard to beat. Any future challenger needs a spring that jumps above 20 °C early and an autumn that stays generous into the third week of September, all without a single miss in between.
People planning ahead for summer events, or simply wondering what a truly warm London season looks like, can look at 2022 as the benchmark. It was not merely a hot summer; it was a long one, and the length of that warmth is what made it exceptional. The 101-day stretch remains a powerful reminder that occasional extremes are part of London's climate record, and that the duration of summer warmth can vary dramatically from year to year. As the climate evolves, the frequency of such long spells may change, but the 2022 season will stand in the record books as the definitive long summer of the series so far.
Data source: Met Office, London St James's Park. Period of record: 1912–2025.
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