Highest temperature in London on May 22?

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Market context

London City Airport’s temperature on 22 May will be set by the highest reading recorded there during the official day, with settlement drawing on the final Wunderground history data. The crowd is currently pricing 0% for a very warm outcome, which points to an expectation of a fairly ordinary late-spring maximum rather than a notable heat spike. That is consistent with London’s May climate, where average highs sit in the mid-teens Celsius and extremes above 27C are uncommon even in a warm spell.

The main historical guide is how quickly south-east England can swing from cool, cloudy conditions to brief warmth under a ridge of high pressure. London’s all-time May record is 32.8C, but that belongs to rare one-off events rather than the usual distribution. More relevant for this market is that values in the high 20s tend to require a clean, sunny day with little marine influence; once cloud cover or a breeze off the North Sea develops, the ceiling usually sits much lower.

For traders, the key catalysts are the Met Office forecast updates, any changes to the pressure pattern over southern England, and whether sunshine lasts long enough into the afternoon for London City Airport to print a late peak. The 12:00 UTC settlement window means the day’s maximum must be registered by midday, so overnight and early-morning forecast revisions matter more than late-day warmth. Wunderground’s final station record will decide the outcome, so any slight adjustment to the airport’s observed peak temperature can move the market’s exact range.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on May 22? across five venues. We show live odds for Polymarket-based markets (sourced from the Polygon order book); for other venues we list platform attributes, since the comparable contracts are not exposed via a public API on every venue. Every CTA points at PolyGram — the application we operate, where you trade directly against the Polymarket order book at 0% fees.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

FAQ

Where can I trade this market with the lowest fees?

On PolyGram, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

PolyGram is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What does it cost to trade on PolyGram?

Zero. PolyGram routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.