Highest temperature in London on May 20?

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Market context

London City Airport’s official maximum on 20 May has already landed at 20°C in the market’s referenced comparable data, which is the kind of mid-teens-to-low-20s outcome that usually dominates London in late spring. Against that backdrop, the implied probability for a specific outturn sitting at 0% looks like a clear underdog position, with consensus effectively treating the “favourite” as a repeat of a mild, dry day rather than a sharp warm-up or cool spell. For comparison, London’s May climate norm is a daytime high in the high teens Celsius, so anything materially above the low 20s needs a properly warm airmass; anything much below that typically requires cloud, wind, or rain suppressing the afternoon peak.

For traders, the key dependency is the finalised London City Airport reading on Wunderground, not a city-wide average, so local coastal influences, sea-breeze timing and any brief shower activity can matter more than broader London conditions. The main watchpoint is the afternoon heating window before the 12:00 UTC settlement cut-off: if skies clear early and winds stay light, the station can finish a degree or two higher than nearby sites; if cloud lingers, the ceiling stays tight. No major weather event is needed here, just the exact station observation, so the contrarian angle is that small mesoscale differences can decide whether a consensus favourite holds or whether an overlooked temperature band becomes the value spot.

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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

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.

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 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.