Highest temperature in London on August 3?

Platform comparison

Market context

The settlement depends on the highest temperature recorded at London City Airport on 3 August, so the key question is whether the day stays in the low-to-mid 20s Celsius or breaks higher during the afternoon peak. At 02:35 UTC, broad August guidance for London still points to typical daytime highs around 21-22°C, while day-specific outlooks for 3 August cluster around the mid-20s, with some services showing roughly 24°C and others as high as 29-33°C for London more generally.[2][5][15][11]

That makes the current 0% YES reading on Polymarket look far below the range suggested by the weather context, though it may reflect the market’s exact settlement terms rather than a city-wide forecast. Comparable books also present this differently: Kalshi-style contracts usually show an implied probability directly, whereas Betfair and Smarkets quote decimal prices/odds, so the same view can look very different across platforms even before fees. On this sort of weather market, the most material divergence is often pricing mechanics and access: Polymarket is crypto-native, while Kalshi, Betfair and Smarkets typically involve fiat onboarding and stronger KYC controls, which can affect who can participate and how quickly prices adjust.

For traders, the main catalysts are the live forecast updates through the morning and early afternoon, because a modest shift in cloud cover, breeze or shower timing can move the eventual station maximum. There are no major scheduled announcements tied to the event itself, so attention falls on model refreshes and short-term observations from London stations; the practical dependency is whether clear spells develop enough for London City Airport to print a warmer peak than the citywide average implied by the monthly forecasts.[13][2][5]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares Highest temperature in London on August 3? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. The live probability is the Polymarket mid; the comparison columns summarise each venue's fee structure, KYC, settlement currency and payment rails. Every CTA routes to Polymarket Alternative, which mirrors the Polymarket order book at 0% fees.

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.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

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.

What about Smarkets as an alternative?

Smarkets is a UK betting exchange with a lower default commission (2%) than Betfair. Liquidity on political markets is below Polymarket, comparable to Kalshi. Geo-blocked in many jurisdictions.

Which platform is accessible globally?

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