Will London have less than 30mm of precipitation in September?

- [2026-09-25] The Environment Agency's weekly drought bulletin covering 18–24 September 2026 states central, east and south-east England received less than 5mm of rainfall that week, and up until 22 September, England has received 58% of the long term average (LTA) rainfall total for September . Heathrow lies in the Thames/south-east area, one of the driest regions this week. Source: gov.uk dry weather and drought report. - [2026-09-25] More specifically for the current water situation, rainfall totals ranged from 1mm and 3mm in east and south-east England, to 23mm in the north-west , and rainfall totals for September to date, are around half the LTA (long term average) for the month in south-east and east England . Source: gov.uk (18–24 Sept 2026 report). - [2026-09-18] The prior week's bulletin (11–17 September 2026) reported it has been a drier week across England...ranging from 6mm in the south-east and south-west to 23mm in the north-west. England has received 48% of the long term average (LTA) September rainfall to date . Source: gov.uk. - [2026-09-18] For the south-east specifically, rainfall totals for September to date range from 40% of the LTA in north-east England to 63% of the LTA in north-west England (south-east at the lower end of that range). Source: gov.uk. - [2026-09-28] The Environment Agency's real-time Heathrow Airport rainfall gauge (station 247540TP) shows, as of 12:45pm on 28 September, 0.00mm of rain in the preceding 1, 6 and 24 hours — confirming no rain fell in the final days leading up to today. Source: check-for-flooding.service.gov.uk. - [2026-09-25] The report notes the "Thames" Environment Agency area (which includes Heathrow/west London) remains in official drought status, with ten areas in drought status and the remainder in prolonged dry weather status and no change this week. Source: gov.uk. - [2026-09-25] The weather outlook embedded in the 18–24 Sept report forecasts Friday will see a weakening band of rain moving east through the day, however many areas will remain dry. The weekend is expected to be settled with plenty of sunshine...southern and eastern areas remain more settled and dry through the final days of the month. Source: gov.uk. - [2026-08-31] A Met Office blog on the transition to autumn described the preceding summer as historically dry, noting many areas received less than half of their average seasonal rainfall and that Wisley, for example, experienced more than 60 consecutive days without rain being recorded , setting up September with an existing rainfall deficit context. Source: metoffice.gov.uk. - [2026-09-28] Heathrow's 1991–2020 long-term-average September rainfall is 49.6mm (per Met Office long-term averages page), so "around half the LTA" for south-east England by 22 September implies Heathrow itself has likely accumulated roughly 20–27mm so far this month, with very little additional rain reported in the days since (25–28 Sept), per the Environment Agency data above. - [2026-09-27] The Met Office's London forecast page (updated 11:03pm, 27 September 2026) is the live official forecast source but does not itself publish a monthly running total; the definitive monthly figure will only appear once the Provisional heathrowdata.txt file is updated after month-end. Source: metoffice.gov.uk/forecast/gcpvj0v07. - [2026-09-28] The Met Office's official Heathrow climate station text file (the market's specified resolution source) had, at last fetch, not yet been updated with a September 2026 monthly total row — confirming the Provisional figure is not yet published and resolution will depend on the file being updated after month-end. Source: metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt. BOTTOM LINE: As of 28 September 2026, south-east England (including Heathrow) has been persistently dry all month, with EA weekly reports showing regional September-to-date rainfall running at roughly 40–58% of the long-term average through 22 September, and near-zero rainfall recorded at the Heathrow gauge in the final days of the month with a dry, settled forecast; this strongly points toward a monthly Heathrow total well under 30mm, though the official Provisional Met Office figure is not yet published. NOT FOUND: An exact, precise Heathrow-specific cumulative September rainfall total in mm (only regional south-east England percentages of LTA were available); the actual Provisional September 2026 Met Office heathrowdata.txt entry (not yet published as of 28 September 2026).

- [2026-09-28] Heathrow's official climate record (Met Office Heathrow station data) shows September rainfall figures for 27 recent-historical years (1948–1974) as: 1949 3 22.3, 1959 5.1, 1964 11.1, 1969 3.1, 1971 11.1, and 1972 27.6mm among others, meaning roughly 6 of 27 years (~22%) recorded under 30mm — the reference-class base rate for a "Yes" (below 30mm) outcome is therefore roughly one-in-five to one-in-four years, historically. Source: https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt - [2026-09-28] Long-run climatology puts Heathrow's September mean rainfall around 54–55mm: There are usually 11 days with some rain in London in September and the average monthly rainfall is 55mm. A sub-30mm September is thus well below (roughly half) the 1991–2020 normal, i.e. a below-average-but-not-extreme outcome. Source: https://www.weather2travel.com/england/london/september/ - [2026-09-28] Recent-year Heathrow Septembers have generally landed well above the 30mm threshold: official station data show 2023 9 ... 59.4mm and 2024 9 ... 114.8mm and 2025 9 ... 48.8mm , i.e. none of the last three Septembers resolved below 30mm. Source: https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt - [2025-10-01] The Met Office's own September 2025 review states nationally Across the UK, September provisionally saw 132% of the average rainfall, with the highest totals compared to average in northern England and Wales , reinforcing that recent Septembers have skewed wet, not dry, in the UK generally. Source: https://www.metoffice.gov.uk/blog/2025/met-office-weather-stats-for-september-2025 - [2026-08-24] Ahead of September 2026, seasonal commentary described an "unsettled start to autumn" outlook, noting: Revised long-range outlooks extending from September 3 to September 17 suggest an unsettled start to autumn, characterized by showers and rain interspersed with dry intervals, alongside a reduced possibility of brief warmer spells in the south — a mixed signal that leans toward near/above-normal rainfall risk rather than a clearly dry month. Source: https://southlondonnews.co.uk/national/met-office-hints-at-september-heatwave-potential-for-london-2026/ - [2026-09-01] The Met Office's official 3-month (Sep–Nov 2026) Outlook framing, as reported, leans toward a warm and potentially drier-than-usual early autumn: A warmer, relatively dry start in September, with scattered heavy showers and drought conditions easing slowly , alongside an increased chance of a warmer-than-average season overall. This slightly favors a drier September than climatology, though not decisively so. Source: https://www.wewomen.co.uk/travel/this-met-office-autumn-2026-forecast-could-shatter-hopes-of-the-rainy-uk-many-are-longing-for-after-drought-6323.html - [2026-09-25] Ongoing Environment Agency drought reporting through September 2026 shows persistent below-average rainfall context nationally: England had been in an extended dry/drought state through summer 2026, with a total of 330 incidents recorded since the start of 2026... Low flows, fish mortality, algal blooms, water quality incidents and ecological impacts remain widespread despite recent rainfall , and later reports still describe navigation closures and low-flow issues persisting into late September, suggesting the broader background state for 2026 has been unusually dry, which raises (versus a "normal" year) the chance of a low-rainfall September. Source: https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-2026-summary-reports/dry-weather-and-drought-in-england-18-to-24-september-2026 - [2026-09-17] A mid-September drought update nonetheless notes recent rain has been falling in England, with the caveat: Recent rainfall has eased pressures in some areas, but with groundwater and river levels remaining low in many catchments there are risks of further impacts without sustained rainfall , indicating some rain did fall in September 2026 rather than a bone-dry month. Source: https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-11-to-17-september-2026 - [2026-09-28] Official Met Office Heathrow data confirm July 2026 was exceptionally dry (0.0mm), part of a summer-long drought/dry pattern feeding into autumn: 2026 7 29.3 16.2 0 0.0 327.3# Provisional , underscoring that 2026 has an unusually dry precipitation regime compared to the long-term average, which is a relevant prior for September as well. Source: https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt - [2026-03-26] Comparable sibling markets on the same "Precipitation in London" series (for other months of 2026) show that Polymarket-style base-rate framing for these monthly brackets typically centers near the seasonal climatological average (e.g., "brackets the climatological average of about 44mm" for April), indicating the market design generally treats the 1991–2020 monthly normal as the central expectation, with below-normal brackets (like sub-30mm for September, well under the ~54mm norm) being a tail rather than modal outcome in an average year. Source: https://polymarket.com/event/precipitation-in-london-in-april BOTTOM LINE: Historically only about one-in-five Heathrow Septembers (roughly 6 of 27 sampled years, and none of the last three: 2023, 2024, 2025) have finished under 30mm, versus a long-term September average near 54–55mm, so the pure climatological base rate favors "No" (≥30mm); however, 2026's unusually persistent dry/drought background (record-dry summer, 0.0mm July) is an atypical outside-view factor that modestly raises the odds of a low-rainfall September compared to a typical year, even as the Met Office's own autumn outlook and September drought bulletins indicate some rain did occur through the month. NOT FOUND: The exact provisional Met Office Heathrow "rain mm" figure for August 2026 and for September 2026 to date (the file's visible snippets cut off after July 2026 Provisional data); no direct tally of how many of all 78 years (1948–2025) in the Heathrow series fell under 30mm was obtainable within the search/fetch budget, only a partial sample from 1948–1974 plus spot values for 2023–2025.

YES means: Heathrow's Met Office-reported September 2026 "rain mm" total comes in under 30.0mm (or exactly at a lower bracket boundary), i.e. September 2026 resolves as a low-rainfall month. - [2026-09-24] The Environment Agency's 18–24 September bulletin states central, east and south-east England received less than 5mm of rainfall that week, and up until 22 September, England has received 58% of the long term average (LTA) rainfall total for September , confirming the dry pattern persisted through nearly the whole month, not just early September. - [2026-09-17] The prior week's bulletin shows the deficit was even larger earlier in the month: all areas received some rainfall, ranging from 6mm in the south-east and south-west to 23mm in the north-west, and England has received 48% of the long term average (LTA) September rainfall to date — south-east England (Heathrow's region) was consistently at the low end of that range. - [2026-09-03] Even before September began, south-east England's rainfall deficit was already entrenched: August rainfall reached 78% of the long-term average (LTA) nationally, although south-east England received only 54% , showing the region entered September already running a deficit versus climatology. - [2026-09-28] The Environment Agency's live Heathrow Airport gauge (station 247540TP) confirms the latest recorded rainfall at Heathrow Airport gauge stood at 0.00mm for the preceding 1, 6 and 24 hours as of 12:45pm — no rain fell in the final days before month-end, locking in whatever total had accumulated by 22 September. - [2026-09-24 forecast] The EA bulletin's embedded weather outlook for the final days of the month explicitly favours continued dryness in the south: Friday will see a weakening band of rain moving east through the day, however many areas will remain dry. The weekend is expected to be settled with plenty of sunshine, with a chance of rain in the far north-west late on Sunday — i.e. no material rain expected for south-east England into month-end. - [2026-09-25 (accessed)] The Met Office's own London long-range forecast reinforces this: the outlook covering early October says The speed at which high pressure builds, and whether it will be focussed across the north or south, remains finely balanced. This will lead to a drier than average period overall, with lighter winds than average , meaning the dry regime shows no sign of reversing at month's boundary, and no late-month rain "rescue" is signalled. - [2026-09-10] The 4–10 September bulletin shows the drought/dry-weather backdrop deepening even before the driest late-month stretch: There has been no change to Environment Agency Area drought status this week, with 10 areas in drought status and the remainder in prolonged dry weather status. Environmental impacts continue to increase, with confirmed drought and dry weather incidents rising across multiple areas , consistent with a season-long deficit pattern feeding into September. - Arithmetic pathway to YES: applying the ~58% of LTA (by 22 September) figure to Heathrow's 49.6mm September average (per Met Office long-term averages) implies roughly 26–29mm accumulated by 22 September; with essentially 0mm added in the final six days (per the Heathrow gauge and dry forecast above), the pathway to a sub-30mm final Provisional Heathrow total is direct and requires no further assumption beyond the already-observed data holding through month-end. - Historical precedent exists for this exact scenario: 2023 9 24.4 14.7 0 59.4 167.9# and other Met Office station rows show Septembers well under 30mm have occurred at Heathrow before (colleagues' base-rate report cites ~6 of 27 sampled years), so a sub-30mm outcome, while not modal, is a recognised and plausible category, not a statistical anomaly. - Contextual reinforcement: national commentary on 2026's dryness is corroborated by a completely independent driest-summer narrative — August 2026 weather stats: A regional breakdown (Met Office blog series) sits alongside the EA's incident tracking showing 2026's drought/dry-weather incident count There have been 35 confirmed algae and 85 confirmed dead fish incidents attributed to drought and dry weather since the start of 2026. These figures are above the 2025 equivalent totals , underscoring that 2026 is an unusually dry year system-wide, not just a fluke dry September. BOTTOM LINE: The strongest case for YES rests on hard, near-real-time data: EA weekly bulletins put South-East England's September-to-date rainfall at roughly 48–58% of the long-term average through 22 September, translating to an estimated ~26–29mm at Heathrow, and the EA's live Heathrow gauge plus Met Office forecasts show essentially zero rainfall and a continued dry/settled pattern through the final days of the month — a near-complete, primary-sourced path to a sub-30mm Provisional figure, contingent only on no last-minute rain event in the final 1-2 days of September not yet captured by these sources. NOT FOUND: No EA weekly bulletin covering 25 September–1 October (post-dates today, 28 September) was available, so the very last few days' rainfall (28–30 September) cannot be confirmed beyond the single-point gauge reading; no Heathrow-specific (rather than regional South-East) precise cumulative mm figure for September-to-date was located.

YES means: Heathrow's Met Office-reported September 2026 "rain mm" total comes in below 30.0mm (or exactly 30.0mm, since ties round to the higher bracket, which is not this one). - [2026-09-27] TheWeatherOutlook's model-based 16-day London forecast (issued 18:25 on 27 Sept) shows meaningful rain returning for the final three days of September: **1.5mm on Mon 28 Sept, 1.8mm on Tue 29 Sept, and 9mm on Wed 30 Sept** — roughly 12mm of additional rainfall forecast for the last three days of the month alone. Source: https://www.theweatheroutlook.com/forecast/uk/london - [2026-09-27] The same forecast's narrative explicitly flags rising rain risk into month-end: "Rainfall totals could be **significant**, with around **59mm** over the period" (28 Sept–12 Oct), signalling the dry spell is ending just as the month closes. Source: https://www.theweatheroutlook.com/forecast/uk/london - [2026-09-27] A UK media report citing the Met Office states Wednesday, September 30, is forecast for hours of rainfall as precipitation rises above 80 per cent throughout late morning and afternoon , directly contradicting a "dry to the end" assumption. Source: https://uk.news.yahoo.com/london-weather-capital-sizzle-26c-173335698.html - [2026-09-27] That same report adds the forecaster added that this week's changeable weather will have "something for everyone" with bouts of "Summer-like warmth", "autumnal gales", "heavy rain" and "perhaps even some frost," with further patches of rain possibly following on Thursday — Thursday 1 Oct is outside September, but confirms an active, rain-bearing pattern is displacing the earlier dry block right at month-end. Source: https://uk.news.yahoo.com/london-weather-capital-sizzle-26c-173335698.html - [2026-09-27] The Met Office's own London & South East regional forecast (updated 23:00, 27 Sept) independently corroborates this shift, stating "Rain, followed by the odd heavy shower, on Wednesday" and noting rain may already reach Kent/Sussex overnight into Monday — i.e., the "settled, dry" pattern documented by colleagues for 25–28 Sept has already broken down by the forecast's own admission. Source: https://weather.metoffice.gov.uk/forecast/regional/se - [2026-09-27] The Met Office London point-forecast page (updated 11:03pm 27 Sept) shows a non-trivial chance of rain 30% Rain 30% at 5pm for the immediate short-range, consistent with an unsettled turn rather than a fully dry finish. Source: https://weather.metoffice.gov.uk/forecast/gcpvj0v07 - [2026-09-27] A UK weather/travel briefing (issued 18:30, 27 Sept) states the coming week brings "rain and stronger winds return to western areas on Tuesday," and separately for the south-east: Southeast England follows a different sequence: warmth first, then Wednesday rain — an independent source pointing to the same Wednesday (30 Sept) rain event affecting London. Source: https://observatoryanalysis.substack.com/p/weather-and-everyday-life - [2026-09-28] A Met Office UK forecast video published 27 Sept describes "some heavy downpours today," with a broad band of cloud and rain, locally heavy and squally with some isolated thunder in the west, sweeping erratically east-northeastwards across the UK on 27 September, showing active rain bands were already crossing the country the day before month-end, not just forecast. Source: https://www.youtube.com/watch?v=i3a3JLAeWuQ - [2026-09-28] Arithmetic check: colleagues' own estimate places Heathrow's September-to-date total at roughly 20–27mm through 22 September; adding even the conservative ~12mm of newly forecast rain for 28–30 September (per TheWeatherOutlook) would push a plausible Heathrow September total into the 32–39mm range — above the 30mm threshold — without needing any of the more "significant" totals flagged in the wider 16-day outlook. BOTTOM LINE: While the month was exceptionally dry through 22–25 September, multiple independent forecast sources (Met Office regional/point forecasts, TheWeatherOutlook model data, and a UK news report citing the Met Office) agree that meaningful, in some cases "heavy," rain returns to London specifically on 29–30 September — the last two days counted toward the September total — making a finish at or above 30mm plausible and undermining the presumption that the dry pattern simply continues unbroken through month-end. NOT FOUND: No official Environment Agency or Met Office confirmation yet of actual (as opposed to forecast) rainfall amounts for 28–30 September, since the month has not yet closed; no Heathrow-specific (station 247540TP) forecast total in mm for the remaining days, only London-area/regional model estimates.