Highest temperature in London on May 22?

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Active sub-markets

Market context

The settlement depends on the highest temperature recorded at London City Airport on 22 May 2026, not on a London-wide average or a forecast high. Late-May normals in London are typically in the low- to mid-20s °C, but the city can warm quickly in a settled southerly flow, and recent extremes show that 28°C or above is unusual but not out of reach. That helps explain why the crowd on Polymarket is effectively assigning a near-certain outcome around the upper-20s, while a book such as Betfair or Smarkets would usually present the same view through much shorter decimal prices after commission rather than a simple implied-probability display.

For comparison, the London record for May is far above normal and the Met Office has already observed a very warm spell this month, so traders are really focused on whether the airport’s final reading lands a degree or two either side of the likely band rather than on a broader climate context. On Kalshi, if this event were listed, the key difference would be the contract structure and access: US-facing exchange rules, KYC requirements and market pricing in cents, versus Polymarket’s crypto-settled interface and UK books’ familiar odds format. Wunderground’s final station history is the source that matters for resolution, so any late adjustment in that archive, rather than a London weather summary page, will decide the payout. Catalysts are limited but important: the Met Office observation feed, any evening temperature spike before the 12:00 UTC settlement cut-off, and whether the station records its day’s high before temperatures level off.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in London on May 22? from four platform perspectives: Polymarket (on-chain CLOB), Kalshi (CFTC-regulated exchange), Betfair Exchange (sports book exchange), Smarkets (peer-to-peer betting exchange). Polymarket's live quote comes directly from the Polygon order book; the other three are listed with their platform attributes — fees, KYC, settlement currency, payment options — because a 1:1 contract comparison without API access would be guesswork.

Resolution & payout

Polymarket settles via UMA Optimistic Oracle on Polygon. A proposer posts the outcome with a bond, the two-hour window runs, then the smart contract pays USDC.

Kalshi settles USD through the CFTC-regulated clearinghouse — the cleanest variant, with heavier KYC. Betfair Exchange settles in account currency (GBP/EUR), net of 2-5% commission. Smarkets follows the same model as Betfair with a lower default 2% commission.

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 fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, PolyGram triggers a quick verification flow that finishes in minutes.

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.