Highest temperature in Seattle on August 9?

Platform comparison

Market context

Seattle-Tacoma International Airport likely peaked in the upper 70s Fahrenheit on 9 August, which is consistent with the market’s current 0% YES pricing only if traders are effectively treating the contract as already settled or as a misread of the underlying range. Polymarket shows a bracketed outcome format and crowd-implied probabilities, whereas Kalshi and Betfair typically express the same view as decimal-style prices or odds; Smarkets also uses a commission-based model rather than wide embedded spreads, so the same weather read can look cheaper or tighter depending on venue. Weather Underground’s Daily Observations table is the settlement reference here, not the summary high/low box, so any late correction in the table matters more than the headline display.

For context, Seattle’s August climate normal maximum at Sea-Tac is 79°F, with the record for 9 August at 99°F, so a sub-80°F outcome is common even in a warm month.[2] AccuWeather’s August outlook for Seattle had 9 August at 76°F, while the Polymarket event page itself cites a 77°F daily maximum from National Weather Service observations, which sits squarely in the 76–77°F range and explains why the market is already near certain.[1][3] Historical comparables show that Seattle can spike well above normal, but those hotter cases tend to require persistent inland heat and weak marine influence rather than a standard coastal summer pattern.[11][17]

The main catalysts are the final post-midnight observation sequence, any later revision to the Sea-Tac daily table, and whether the contract’s temperature band matches the published maximum exactly before the cutoff for following-day datapoints. NWS forecast pages for Seattle were updated early on 9 August, and the monthly climate product provides the normal-versus-record context traders use to sanity-check the print.[5][7] On platform choice, Kalshi’s KYC access is broader in the US than Betfair’s limited weather-market availability, while Smarkets’ fee structure can matter more than spread for a low-volatility weather contract; for a market this close to an observed airport reading, execution quality and settlement source discipline matter more than headline odds.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in Seattle on August 9? 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.

FAQ

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

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.

Which platform supports Klarna/SOFORT?

Directly: none. Polymarket accepts only USDC on Polygon. Polymarket Alternative 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.