Highest temperature in London on July 12?

Platform comparison

Market context

London is experiencing a sweltering heatwave with temperatures peaking at 35C on Thursday 9 July, yet the current day, Sunday 12 July, shows a drop to 24C–27C with thunderstorms expected to break the heat later this week [4]. The crowd-implied 0% probability for a specific high temperature on this date reflects the immediate cooling trend, as models predict peak temperatures will remain around 27C before dropping to 24C by Saturday 18 July [4]. Historical data for London City Airport confirms July is the hottest month, with an average high of 72°F (22°C), though recent extremes have pushed well beyond this baseline [3].

Traders should monitor the Met Office’s amber heat alert, which officially expires at 9pm tonight, and watch for the thunderstorms forecast for Thursday 16 July that will end the current heat spell [4]. The resolution source, Weather Underground, will record the highest temperature at London City Airport (EGLC) for all times on 12 July, a station where current observations show 13°C with high humidity and falling pressure [6]. Unlike Kalshi’s decimal odds or Betfair’s spread betting, Polymarket displays this as an implied probability, while Smarkets offers a lower fee structure but requires stricter KYC verification for UK residents, creating divergent entry costs for this weather event.

The divergence in book mechanics means a 0% implied probability on Polymarket represents a near-zero chance of the event occurring, whereas a decimal odds of 1.00 on Kalshi would imply the same but with different fee implications. Given the Met Office warning that temperatures will not reach the previous 35C peak again in this round, the market’s pricing aligns with the forecasted cooling [4]. Traders comparing platforms must note that while Polymarket allows crypto access without traditional banking, Kalshi and Betfair restrict access based on US or UK licensing, respectively, affecting liquidity for this specific London weather contract.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in London on July 12? 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 mid is the canonical probability; the side-by-side columns benchmark fees, KYC, settlement currency and deposit rails so you can choose the venue that fits your jurisdiction and trade size.

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). On-chain settlement clears in minutes — the fastest payout path of the four.

FAQ

What does Polymarket cost vs Kalshi?

Polymarket: 0% fees, only Polygon network costs (~$0.01/trade). Kalshi: up to 7% per trade plus spread. For high-frequency traders, Polymarket is dramatically cheaper.

Is Betfair a Polymarket alternative?

Only partially. Betfair Exchange is UK-focused with a sports-betting emphasis; they have politics markets but with thinner liquidity than Polymarket. Settlement in GBP/EUR, 2-5% commission on winnings.

Which platform is accessible globally?

Polymarket is geo-blocked in the US/UK/EU. Kalshi is US-only. Betfair and Smarkets are UK-restricted. Kalshi Alternative UK has a different geo footprint and routes to Polymarket's order book at 0% fees.

Are all these platforms regulated?

No. Kalshi is CFTC-regulated (US). Betfair and Smarkets are UK Gambling Commission licensed. Polymarket operates without explicit regulation — a different risk profile than a regulated sportsbook.

Which platform supports Klarna/SOFORT?

Directly: none. Polymarket accepts only USDC on Polygon. Kalshi Alternative UK offers a fiat on-ramp via Klarna or SOFORT (DE/AT/CH) and converts internally to USDC for the Polymarket order book. T+1 processing.