Highest temperature in London on May 25?

Platform comparison

Active sub-markets

Market context

On 25 May 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The settlement hinges on data from Weather Underground's historical records for that specific station, with the window closing at noon UTC. Polymarket's 0% implied probability on this particular outcome suggests either extreme confidence in alternative ranges or minimal liquidity; by contrast, Kalshi's weather markets often display tighter spreads on UK temperature bands due to their regulatory structure and KYC reach into institutional traders. Betfair and Smarkets, operating under different odds formats (decimal vs fractional), may show divergent probability representations for the same underlying event, though their settlement sources typically align.

London's May temperatures have historically ranged between 12°C and 28°C, with the long-term average high around 19–20°C. The 2022 heatwave saw May peaks exceed 25°C in parts of southern England, though City Airport—situated near the Thames estuary—typically records slightly cooler maxima than central London due to maritime influence. This context matters: traders comparing across platforms should note that Polymarket's decimal odds format can obscure whether the crowd genuinely expects cooler conditions or simply favours other temperature brackets with better odds ratios.

The Met Office publishes extended forecasts from mid-May onwards; monitoring their 16-day outlook from early May will signal whether anomalous warmth is expected. Atmospheric patterns in late spring depend heavily on jet stream positioning and Atlantic pressure systems, typically confirmed only 10–14 days ahead. Fee structures differ materially—Polymarket charges 2% on withdrawals, whilst Kalshi's flat-fee model may favour smaller position sizes on low-probability outcomes.

Methodology

We read Highest temperature in London on May 25? 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

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). PolyGram routes every trade directly into Polymarket's on-chain settlement, which is why payouts land fastest.

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 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.

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.