Highest temperature in London on May 20?

Platform comparison

Active sub-markets

Market context

London City Airport’s observed maximum on 20 May was well above the lower temperature bands, with the Met Office-style local station record used for this market pointing to a warm afternoon rather than a cool one. That matters because the contract settles on the single highest reading during the day, so even a brief early or late peak can decide the outcome.

For context, mid-May in London is usually much cooler than the conditions seen this week. Climate normals and recent forecasts from AccuWeather put typical highs in the high teens Celsius, while Polymarket’s own London temperature markets for adjacent dates have already priced 20°C-plus outcomes as the clear favourites. A prior London market for 20 May also resolved at 20°C, underlining that late-spring warmth is plausible, but not routine, and that a one-day spike can sit well above the monthly average.

The main traders’ focus is the day’s official station trace rather than broad city weather. If the airport’s afternoon high comes in at or above the nearest quoted band, the market should follow that reading once Wunderground finalises the daily history. The key dependency is any late update to the station’s recorded maximum, but with the settlement window ending at 12:00 UTC on 20 May, the relevant move is already determined by the day’s early-to-midday warmth.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on May 20? 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

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

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's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

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 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.