Highest temperature in Seoul on July 21?

Platform comparison

Market context

Seoul is currently gripped by monsoon rains that have pushed relative humidity to 100% and dew points to 77°F as of Monday evening, suppressing daytime highs significantly below seasonal norms[1]. This immediate deluge contrasts sharply with the dry heat typically required to breach 35°C, explaining why the market assigns a 0% probability to any outcome implying extreme heat. The stationary front moving north from Jeju Island is expected to continue soaking the Chungcheong region and southern provinces, keeping cloud cover dense over Incheon and Seoul through the settlement window[3].

Historical July data for Seoul shows daytime maximums averaging 28°C, with frequent rainfall and 16 rainy days per month, making extreme heat events rare during the active monsoon phase[4][5]. Comparable cases from early July 2026 saw apparent temperatures reach only 31°C amidst heavy rain, while typical highs hover in the upper 20s rather than the 30s or 40s required for outlier outcomes[3][8]. The current 0% implied probability aligns with this pattern, as the wet, humid conditions act as a natural thermostat preventing the temperature spikes seen in dry summer spells.

Traders should monitor the Korea Meteorological Administration’s updates on the stationary front’s northward progression, which dictates whether rain persists or clears to allow solar heating[3]. Key dependencies include the timing of scattered showers forecast for the Gyeongsang and Jeolla regions, as a sudden front collapse could theoretically expose inland areas to higher temperatures, though current forecasts suggest continued cloud cover[3]. The settlement relies on Wunderground data from Incheon Intl Airport Station, where morning lows are already forecast at 22°C, reinforcing the likelihood of a moderate maximum rather than an extreme one[3].

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is Prediction Today. 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 Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Prediction Today trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

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.