Highest temperature in Seattle on August 9?

Platform comparison

Market context

Seattle’s temperature on 9 August will be determined by the **highest observed reading** at Seattle-Tacoma International Airport, with Weather Underground’s Daily Observations table taking precedence over any summary high if they diverge. That matters for platform comparison: Polymarket-style temperature contracts are quoted as **implied probabilities**, whereas Kalshi and Betfair typically surface **price in cents or decimal-style odds**, and Smarkets uses an exchange format with **commission on net winnings** rather than a built-in spread. Robinhood’s prediction markets also sit alongside a different KYC and access model, so the same weather outcome can look meaningfully different once fees and eligibility are factored in.

The current 0% YES crowd price is best read against Seattle’s late-summer climatology rather than any single forecast spike. August normals at Sea-Tac are around **79°F** for the daily maximum, with the record for the date far higher, but the market is settled on the actual airport observation, not citywide heat estimates.[2] Comparable August weather contracts on prediction venues have often tightened sharply only when the forecast points clearly away from the seasonal range; where the expected high sits near the upper 70s, market pricing usually remains concentrated around the most plausible band rather than the extremes.[1][11]

For traders, the main catalysts are the **official airport observations** and any late-day shift in marine layer, onshore flow, or cloud cover that affects the afternoon peak. Weather Underground’s daily table is the key resolution source in this market, so a benign-looking “day high” summary is secondary if the observation log differs. The Seattle forecast page was last updated in the morning local time, which is typically when short-horizon temperature markets can still move if the day starts cooler or warmer than expected.[7]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares Highest temperature in Seattle on August 9? 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 Robinhood Prediction Markets, which mirrors the Polymarket order book at 0% fees.

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.

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.

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. Robinhood Prediction Markets 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.