Highest temperature in San Francisco on August 5?

Platform comparison

Market context

San Francisco International Airport’s peak temperature on 5 August will be decided by the day’s highest reading at KSFO, not by the citywide average or the late-evening low. The current Polymarket book is pricing a 0% YES crowd view on the event, but the live ladder is already split across narrow Fahrenheit bands, with 72–73°F and 74–75°F among the front outcomes, which matters because these airport-temperature markets are often clustered tightly around the marine-layer regime rather than swinging into very hot tails.[1]

Historically, San Francisco in August is a low-variance temperature venue, so the market tends to reward traders who anchor to coastal moderation rather than inland heat. That also helps explain why different books can look meaningfully different on the same event: Polymarket shows outcome percentages directly, whereas Kalshi typically displays contract prices in dollar terms that map to implied probability, and Betfair or Smarkets quote decimal-style prices that already embed commission or exchange fees. For a small-range weather market, those presentation differences can make the same consensus look more or less certain depending on whether the book is quoting net odds, gross odds, or a fee-adjusted price.

The main catalyst is the actual intraday weather profile at SFO: marine stratus, timing of morning clearing, and any local offshore push that briefly lifts the afternoon high. The San Francisco Chronicle has flagged a broader California heat wave beginning around 8 August, with temperatures likely to spike from 5–8 August, but that is a regional signal rather than a direct guarantee of a hotter reading at the airport on the 5th.[16] Traders on platforms with stricter KYC access, or those priced in different fee structures, will usually key off the official Wunderground station history once the day is complete, so the market should remain sensitive to any revised airport observation rather than headline city forecasts.[2][7]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in San Francisco on August 5? 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

Polymarket settles via UMA Optimistic Oracle on Polygon. A proposer posts the outcome with a bond, the two-hour window runs, then the smart contract pays USDC.

Kalshi settles USD through the CFTC-regulated clearinghouse — the cleanest variant, with heavier KYC. Betfair Exchange settles in account currency (GBP/EUR), net of 2-5% commission. Smarkets follows the same model as Betfair with a lower default 2% commission.

UK Frequently Asked Questions

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.

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. Kalshi Alternative UK has a different geo footprint and routes to Polymarket's order book at 0% fees.

Polymarket vs Betfair Exchange: which is better for UK prediction trading?

Betfair Exchange offers UKGC regulation, GBP settlement, and potentially tax-free winnings — but focuses on sports and politics only. Polymarket has deeper liquidity, 0% platform fee, global event coverage, and crypto/geopolitical markets Betfair doesn't offer. For UK traders: Betfair for regulated GBP sports markets; Polymarket for broader, global prediction events.

Is Kalshi available in the UK?

Kalshi is a US CFTC-regulated prediction exchange. UK residents can create accounts but must use USD and US payment methods. Kalshi's product range overlaps with Polymarket but with lower liquidity on most contracts. For UK traders, Polymarket typically offers better prices due to higher global volume.