Trade: Highest temperature in Seoul on May 21?

Market context

Seoul’s heat benchmark for 21 May is being set at Incheon International Airport, with settlement based on the day’s highest recorded temperature in Celsius before the noon UTC cut-off. In the market, Polymarket’s order book is currently pricing the event at 0% YES, so the implied probability is effectively absent and any move off zero would have to come from fresh buying or a shift in trader expectations as the day develops.

For context, late-May conditions around Seoul are usually mild rather than hot. Long-run weather references for May put Seoul’s average daytime highs around 21–24°C, with lows in the low teens Celsius, and historical May readings can still produce spikes into the high 20s Celsius on warmer afternoons. That means the relevant question is not whether May can reach warmth, but whether today’s airport reading clears the next published range on the market’s ladder.

The main catalysts are the live temperature trace through the morning and any local weather changes affecting the airport site, especially sun, cloud and rain bands. If skies stay clear, the day can warm quickly; if showers arrive, the ceiling falls back. Traders should watch the hourly forecast updates and the official Wunderground history page for Incheon once readings are finalised, as that source determines the outcome rather than city-centre conditions.

Sources: 1 · 2 · 3 · 4 · 5

Resolution source

This market settles from the official outcome published at https://www.wunderground.com/history/daily/kr/incheon/RKSI. A proposer submits the final result to the UMA optimistic oracle on Polygon; the two-hour dispute window closes and payouts clear in USDC.

Settlement window & payout timing

For this market, the resolution date is 21 May 2026. A UMA proposer can submit the outcome from that moment; the two-hour dispute window closes at 2026-05-21 14:00 UTC, and assuming no counter-claim is staked, winning USDC clears to trader balances by approximately 2026-05-21 15:00 UTC.

If a dispute is filed inside the two-hour window, the outcome escalates to UMA token-holder voting, which extends settlement by roughly 48 hours. Because this market resolves from a publicly verifiable feed (https://www.wunderground.com/history/daily/kr/incheon/RKSI), the probability of dispute is materially lower than the overall 0.5% PolyGram baseline — most disputes occur on markets with ambiguous wording or non-public resolution sources.

Withdrawal pace from your PolyGram balance is non-custodial and immediate — once payout clears, funds are yours to send to any Polygon wallet you control. Funds clear directly to your in-app USDC balance on Polygon. Withdrawals are non-custodial: send to any address you control, typical confirmation under 30 seconds, gas paid in USDC if you'd rather not hold MATIC.

Trading mechanics

Minimum order size on PolyGram is $1.00, with no maximum cap aside from available book depth. Orders route into Polymarket's on-chain CLOB on Polygon; the matching engine pairs YES buyers with NO buyers atomically — every executed trade is settled on-chain with no counterparty risk. For "Highest temperature in Seoul on May 21?", order-book behaviour for this market reflects the underlying volatility of the outcome — patient limit orders typically fill closer to mid than market orders.

The trade ticket includes a slippage box (default 2%, configurable 0.1%-10%) that caps the worst-case entry price. Your maximum loss is your stake — winning YES (or NO) shares pay $1.00 each at resolution. With this market's current book depth ($4K of resting liquidity), a $50 order should fill with single-cent slippage at the displayed mid-price.

PolyGram charges 0% house edge — no spread mark-up, no rake on winnings, no withdrawal fees beyond network gas. The platform earns exclusively from optional features (copy-trade boosts, advanced order types, the yield vault on idle USDC); the trading surface itself is at-cost.

How to trade this market step by step

The mechanics for trading "Highest temperature in Seoul on May 21?" are the same as any other PolyGram event contract. Each YES share resolves to $1 if the event happens, or $0 if it doesn't. The current price between 0¢ and 100¢ is the market's probability estimate, set live by the order book.

1. Sign in on polygram.ink with your email — no full KYC under $1,500 lifetime trading volume.
2. Deposit USDC on Polygon (lowest fees, ~$0.01 per transaction) or Ethereum. Funds credit after 12 confirmations.
3. Pick a side. Buy YES if you believe the event will happen; buy NO if you think it won't. The current YES price reflects the market's collective probability.
4. Size your position. If you stake 100 USDC at 50% YES, you'll receive shares that pay $200 if YES resolves true — a 100% gross return. If NO resolves, your shares are worth $0.
5. Set risk controls (optional). Stop-loss, take-profit, and limit-order types all supported. Use the trade ticket's slippage box to cap your maximum entry price.
6. Wait for resolution. When the event resolves on-chain via the UMA optimistic oracle, the winning side settles to 100¢ automatically and USDC hits your balance within seconds. Withdrawable to any wallet you control.

How active is this market?

$176K in lifetime turnover and $4K of resting liquidity puts this market in the top 30% by volume for weather contracts on PolyGram. Order-book depth is thin — large orders may need to be split across the book or executed as limit orders.

Last 24 hours alone saw $152K in turnover, well above the lifetime daily-average for this market — a clear sign of news catalysing trader activity right now.

The market has been open for under a month — fresh enough that information asymmetry remains a real factor.

Higher-volume markets tend to have tighter spreads and faster price discovery — meaning the displayed YES/NO percentages are more likely to reflect the true crowd-implied probability rather than a single trader's directional view.

Key terms

YES / NO share

A binary outcome token that pays $1.00 if the underlying claim resolves true (YES) or false (NO), and $0 otherwise. The market price between 0¢ and 100¢ is the implied probability.

CLOB

Central limit order book. The matching engine that pairs YES buyers with NO buyers (effectively the same trade). Polymarket's CLOB on Polygon executes trades on-chain via the conditional-tokens framework.

Liquidity

USDC capital sitting in resting limit orders inside the order book. Deeper liquidity means smaller slippage on large trades and a tighter bid-ask spread.

UMA optimistic oracle

The on-chain dispute system that settles each Polymarket market. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution.

Slippage

The difference between the displayed mid-price and your fill price. Affects market orders most; limit orders avoid slippage but may take time to fill.

Conditional token

ERC-1155 outcome share issued by Gnosis Conditional Tokens on Polygon. The token type that resolves to $1.00 or $0.00 at settlement.

This market's resolution criterion

For "Highest temperature in Seoul on May 21?", the resolution criterion is: This market will resolve to the temperature range that contains the highest temperature recorded at the Incheon Intl Airport Station in degrees Celsius on 21 May '26. The resolution source for this market will be information from Wundergrou…

See the full prediction-market glossary →

Frequently asked questions

Risk and regulatory note

Prediction-market positions can lose 100% of staked capital. Outcomes are uncertain by definition — historical accuracy of crowd-implied probabilities is high in aggregate but not for any single market. PolyGram does not provide investment advice. Trade only with capital you can afford to lose. For "Highest temperature in Seoul on May 21?", the considerations above apply directly — Trade size should reflect the binary nature of the payoff: even a 70% probability event resolves NO 30% of the time, so any single position can lose 100% of staked capital.

Regulatory status varies by jurisdiction. Germany, the United States, and most EU countries treat Polymarket-style event contracts under one of three frameworks: financial derivative, gambling product, or unregulated novel asset. Consult local counsel before trading.

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