Seoul Temperature on May 21: Can It Hit Twenty-Two?

Seoul’s weather on May 21 sits at the center of a tight prediction market call. The contract asks whether the highest temperature that day will reach 22 degrees Celsius or above. Traders currently put that at 36 percent. That’s a minority position, but momentum is moving fast in its direction.

The contract resolves at 2026-05-21 12:00:00. The current market split sits at YES (0.36) versus NO (0.64), with total volume at $19,603 and 24-hour volume nearly matching that at $19,052. Liquidity stands at $22,087. These are thin numbers. At this volume level, a single well-timed trade can reprice the contract sharply. Here’s what the measurements are telling us about which side of that split holds up.

How the Seoul Temperature Contract Works

This contract resolves YES if the highest recorded temperature in Seoul on May 21, 2026 reaches 22 degrees Celsius or above. Polymarket sources the resolution from official meteorological data for the Seoul area. The contract closes at 2026-05-21 12:00:00. A YES payout requires the peak daily temperature to clear that specific threshold, not just approach it.

• YES (22°C or higher): Price 0.36, implied probability 36%
• NO (below 22°C, covering outcomes of 21°C, 20°C, 19°C, 18°C, 17°C, 16°C, 15°C, 14°C, 13°C, 12°C or below): Price 0.64, implied probability 64%

The NO side wins if Seoul’s peak temperature on May 21 lands anywhere below 22 degrees. The Korea Meteorological Administration typically reports daily high temperatures through its automated surface observation network. Missing the threshold by even a single degree keeps NO in the money. Mid-May in Seoul averages daily highs in the 19 to 22 degree range, which is exactly why this market is close enough to argue about.

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Momentum and Market Signals

The momentum composite here is notable. A combined 7.5 percent gain over both the one-hour and 24-hour windows, alongside a trend score of 47.87, points to a single directional push into the YES side. The most likely driver is updated short-range forecast data for Seoul on May 21. When numerical weather prediction models update and shift a peak temperature forecast closer to or above 22 degrees, traders reprice quickly.

Total volume at $19,603 and liquidity at $22,087 are thin by any standard. The market is pricing uncertainty, not science. At this depth, two or three larger trades can swing the probability by five to ten percentage points. The 36 percent YES price should be read as directionally meaningful but not deeply anchored. New forecast data or an observed warm spell in the days leading up to May 21 would test that anchor hard.

• 1h change (+7.5%) and 24h change (+7.5%): YES side gained ground consistently across both windows, suggesting fresh weather forecast data rather than a one-off speculative trade drove the move.
• Trend score (47.87): Sits below 50, indicating momentum is real but not yet dominant. The market has not flipped conviction.
• Volume ($19,603 total, $19,052 in 24 hours): Almost all trading activity happened in the last day. This is a fresh and active market, not a stale one.
• Liquidity ($22,087): Below the threshold where large institutional positions can enter quietly. Price moves here are amplified.
• Open interest ($0): No locked positions outstanding, meaning the market is entirely driven by current order flow.

Lines Analysis: Seoul Temperature on May 21

Seoul’s May climatology is the starting point. The Korea Meteorological Administration records average daily highs of around 19 to 22 degrees for the third week of May. That range straddles the contract threshold almost perfectly. The YES case rests on Seoul landing at the warmer end of its typical range, or running slightly above it. Synoptic patterns that bring southerly or southwesterly flow into the Korean Peninsula can push temperatures well above seasonal norms. A high-pressure system anchored over the Yellow Sea or southern China, combined with strong solar radiation on a clear day, has historically driven Seoul to 23 or 24 degrees in mid-May.

The NO case is straightforward. Seoul sits in a region where late spring temperatures are frequently moderated by maritime air from the Yellow Sea or frontal systems tracking through Northeast Asia. If a front passes through on May 20 or early May 21, or if onshore flow dominates, the daily high can easily stall at 18 to 21 degrees. The alternative outcomes listed in this contract cover a wide band below 22 degrees, which is exactly why 64 percent of market capital currently sits on the NO side. The probability space below the threshold is spread across many outcomes, but the collective bet is that Seoul stays under 22.

• Korea Meteorological Administration short-range forecasts for May 21 will be the single most important data point as resolution approaches.
• Synoptic weather maps showing high-pressure positioning over the Yellow Sea would support YES.
• A frontal passage or cold trough over the Korean Peninsula on May 20 to 21 would collapse YES probability rapidly.
• European Centre for Medium-Range Weather Forecasts ensemble data for the Seoul region, if available, would show forecast spread around the threshold.
• Observed Seoul temperatures on May 19 and 20 will function as a real-time calibration signal for traders.

At $19,603 total volume and 36 percent YES, the market is not settled. The data favors NO based purely on the balance of outcomes below the threshold, but the momentum signal over the last 24 hours says traders are finding fresh reasons to buy YES. Weather markets reprice fast near resolution. The next 24 hours of forecast updates matter more than anything in this contract’s history.

LINES VERDICT

Lean NO, But Watch the Forecast

The 64 percent NO position reflects reasonable Seoul climatology for mid-May, and the breadth of outcomes below 22 degrees gives the NO side structural probability. But thin liquidity means fresh forecast data can flip this quickly.

What the market says: Thirty-six percent of traders believe Seoul hits 22 degrees or higher on May 21. That’s a meaningful minority with fresh momentum. Volume is thin enough that the price could move sharply before the 2026-05-21 12:00:00 close if a warm forecast update lands.

Key unknown: The Korea Meteorological Administration’s updated 24-hour forecast for Seoul on May 21 is the single data point that will reprice this contract before resolution. If that forecast shows a peak at or above 22 degrees, YES will move fast.

Scientific Context

Seoul’s climate in late May sits in a transitional zone between the cooler spring pattern and the onset of the East Asian summer monsoon. The city’s daily high temperatures during the third week of May show significant year-to-year variability, ranging from below 15 degrees during cold spring intrusions to above 25 degrees during early warm spells. The 22-degree threshold in this contract falls near the upper half of the historical distribution for this date. That positioning is why the NO side holds 64 percent: more historical outcomes fall below 22 than above it for Seoul in mid-May. Any El Nino or La Nina influence on the Western Pacific subtropical high would affect the synoptic setup, but the resolution window here is a single day, making macroscale climate drivers less decisive than the immediate forecast. What moves this contract before 2026-05-21 12:00:00 is short-range model output, not seasonal climate signals.

Frequently Asked Questions

• What does 36 percent probability mean here? It means traders collectively estimate a roughly one-in-three chance Seoul’s peak temperature on May 21 reaches 22 degrees Celsius or higher. Prediction market probabilities reflect current information and shift as forecasts update.
• What does the NO side pay out on? NO pays if Seoul’s highest temperature on May 21 lands anywhere below 22 degrees Celsius, covering outcomes from 21 degrees down to 12 degrees or below. The Korea Meteorological Administration’s official observation determines the result.
• What data would move this market’s price the most? An updated Korea Meteorological Administration or global weather model forecast showing Seoul’s May 21 peak temperature near or above 22 degrees would push YES higher rapidly. A forecast of 18 to 20 degrees would reinforce NO.
• When does this contract resolve? The contract resolves at 2026-05-21 12:00:00. That is the closing window for Polymarket to confirm the official Seoul temperature observation for May 21.
• Is $19,603 in volume enough to trust the price? This is thin volume. At this level, a small number of trades can shift the probability by several percentage points. The 36 percent YES price is directionally informative but not deeply anchored. Treat it as a live signal, not a settled estimate.

This analysis reflects market conditions as of 2026-05-20 15:18:13. Prediction market probabilities are volatile and shift as new data and regulatory decisions emerge, especially as the 2026-05-21 12:00:00 resolution date approaches. Lines.com does not accept bets or provide financial or gambling advice. All market outcomes are uncertain.