Highest temperature in London on May 20?

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Active sub-markets

Market context

Polymarket is currently pricing this London temperature contract as a near-certainty against a high outcome, with the market at 0% YES for a very warm reading on 20 May. The contract settles on the highest temperature recorded at London City Airport Station, using the final Wunderground history entry for that day, and traders on Polygon are effectively buying and selling conditional tokens in USDC against that single station observation. Because settlement depends on a fixed hourly-to-daily maximum rather than a broader city average, the gap between a warm afternoon elsewhere in London and the actual EGLC reading can be material.

The historical frame is straightforward: London in May often sits in the mid-teens Celsius, with warmer spells capable of reaching the low 20s, but these are not the norm. The Met Office has recently highlighted how quickly early-season warmth can push parts of southern England above 20°C, yet official observations still show strong day-to-day variability. That makes a zero-probability market plausible when the forecast profile points to a cooler or mixed day, particularly if the airport station sits a little lower than inland parts of the capital.

For traders, the key inputs are the short-range Met Office forecast, any changes to cloud cover or wind direction, and the timing of the daily maximum near the settlement window at 12:00 UTC. London City Airport can run a few degrees below warmer suburban sites, so a last-minute shift in sea breeze, cloud, or frontal timing matters more than headlines about “London heat” in general. Recent Met Office commentary on the UK’s May warmth shows the pattern to watch: one brief warm peak can lift temperatures sharply, but a return to cooler air can cap the airport reading well below citywide anecdotes.

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

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.

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.

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.

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.