Highest temperature in Seoul on June 21?

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Market context

Seoul’s hottest reading at Incheon Intl Airport Station on 21 June will be a single-day maximum, so the practical question for traders is where the afternoon peak lands rather than where the day starts. For June in Seoul, average daily highs typically sit in the high 20s Celsius to low 30s Celsius, with WeatherSpark showing June highs rising from about 25°C to 27°C and only rarely pushing much above the upper 20s to around 31°C.[2] On Polymarket, the market is already clustered around **27°C** and **26–28°C** bands, which is consistent with a summer distribution concentrated near those values rather than in the low 30s.[1]

For probability framing, a 0% YES on one exact outcome is not unusual in temperature markets when the implied mass is spread across adjacent integer bins. Programmatically, this is the sort of contract that is usually approached by tracking live airport observations, the forecast-to-observed gap, and any late-day convective heating that could nudge the maximum by one degree. The historical tail risk is real: South Korea has seen severe summer heat extremes, including an all-time national high of 41.0°C at Hongcheon, and recent summers have produced record-breaking heat across the peninsula.[3][4] That does not mean Seoul will reach those levels, but it explains why the upper bins can reprice quickly if forecasts turn hotter.

The main catalysts are short-horizon weather model updates, cloud cover, rainfall timing, and sea-breeze behaviour, because those factors determine whether the daily maximum is capped in the mid-20s or reaches the upper 20s. A trader using scripts or conditional orders would typically watch forecast revisions from the evening and overnight cycles, then compare them with the first morning observations and any precipitation nowcasting, since the settlement source is the day’s highest value at Incheon Intl Airport Station on Weather Underground.[1] If the afternoon forecast drifts towards 28°C or above, the current 0% reading can move sharply even without any official announcement.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Highest temperature in Seoul on June 21? on the five venues with material liquidity for prediction markets. Live odds come from the Polymarket Polygon order book — the only source that ships real-time data under an open licence. For Kalshi, Betfair and Manifold we list platform attributes (fee, KYC, settlement, payment) instead of fabricated odds, because their APIs use non-comparable contract definitions.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

Where can I trade this market with the lowest fees?

On Polymarket Bot UK, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket Bot UK is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.