Highest temperature in Seoul on May 21?

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Market context

Seoul’s temperature on 21 May is being priced at 0% for the YES outcome on Polymarket, even though the contract itself settles on the highest reading recorded at Incheon Intl Airport Station and pays out in USDC on Polygon via conditional tokens. That implies the market is effectively dismissing any chance that the day’s official top temperature lands in the relevant Celsius range for the YES bucket. With the settlement window already closed at 12:00 UTC, traders are left watching final observations rather than fresh positioning.

For context, late May in Seoul is normally a mild, warming shoulder-season period. Long-run averages put daytime highs around 21°C to 27°C, with weather-spark showing May highs rising from about 68°F to 77°F across the month and rainfall still fairly steady. AccuWeather’s May guidance for Seoul points to highs in the high 20s Celsius and overnight lows in the low teens Celsius. That makes a very hot reading possible, but still less typical than a mid-20s result. Historical data from recent May days also show meaningful spread: Visual Crossing’s Seoul history records a high above 30°C earlier in May 2026, but that is above the usual late-May baseline rather than the norm.

The main catalyst for the final outcome is the station-level observation at Incheon, not the broader Seoul forecast, so traders should care about local coastal influence, cloud cover and any afternoon warming trend near the airport. The Korea Meteorological Administration’s medium-range updates remain the most relevant official background, while the final Wunderground history page for RKSI determines settlement once the day is complete. In practice, conditional-token markets like this move on whether the observed maximum prints in the next band up or down, so any late spike in the official airport record is what matters now.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to PolyGram, which mirrors the Polymarket order book directly.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

FAQ

Where can I trade this market with the lowest fees?

On PolyGram, 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.

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 does it cost to trade on PolyGram?

Zero. PolyGram routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, PolyGram triggers a quick verification flow that finishes in minutes.