Shanghai May 20 Low Temp: Can 21°C Hold?

Shanghai sits at the edge of a meteorological call that expires in less than 24 hours. The question is simple: will the city’s overnight low on May 20 land at exactly 21°C? The market says probably not. At 24.5% implied probability, traders are pricing this specific outcome as a long shot, with the weight of capital sitting firmly on alternative temperatures.

Total volume on this contract is $1,486, with $1,266 of that trading in the last 24 hours. Liquidity sits at $12,361. That thin volume means any fresh weather data or model update could move this price sharply before the 2026-05-20 12:00:00 resolution window closes.

How the Shanghai Low Temperature Contract Works

This market resolves YES if Shanghai’s official lowest temperature on May 20, 2026 is recorded at exactly 21°C. The resolution source is Polymarket’s designated data provider for this contract. If the overnight low lands at 20°C, 22°C, or any other value, the 21°C contract pays out nothing and the alternative outcomes determine winners.

• YES (21°C): Priced at 0.25, implying 24.5% probability.
• NO (any other temperature): Priced at 0.76, implying 75.5% probability.

Missing 21°C is straightforward. Shanghai’s overnight low needs to land anywhere else on the temperature ladder. May in Shanghai typically sees lows ranging from the high teens to the mid-twenties Celsius. The spread of competing outcomes (15°C or below through 25°C or higher) reflects genuine uncertainty about where exactly the needle stops. The 75.5% NO side is not a bet that temperatures will be extreme. It is simply a bet that 21°C is not the exact landing spot.

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Momentum and Market Signals

The momentum composite (0.0% on both the 1-hour and 24-hour windows, trend score 25.21) tells a clear story: nothing has moved this contract. No new model runs, no revised forecasts, and no official weather announcements have hit the market in the last day. Price has been essentially flat since open.

$1,266 in 24-hour volume against $12,361 in liquidity is a thin ratio. This is a low-conviction market where a single large trade or a surprise overnight forecast update from China Meteorological Administration could shift the price meaningfully before resolution. The $1,486 in total volume underscores this is a niche temperature contract, not a heavily traded event.

• 1h and 24h change both read 0.0%: The market is dormant. No catalyst has arrived to reprice the 21°C outcome.
• Trend score of 25.21 reflects a stable but bearish lean. The 75.5% NO weight has not shifted.
• Volume below $1,500 total means price can gap sharply on new data. Thin liquidity amplifies any late-breaking signal.
• Open interest at $0 suggests positions are minimal and the contract has not attracted sustained speculative attention.
• The 30-day range from 0.25 to 0.26 confirms this contract has never priced 21°C as a likely outcome.

Lines Analysis: Shanghai Temperature on May 20

Here’s what the measurements are telling us. Shanghai’s climate in mid-to-late May is transitional. Average overnight lows during this period sit in the 19°C to 22°C band depending on whether cooler northerly flow or warmer southerly maritime air dominates. The China Meteorological Administration’s regional forecasts for late May 2026 would be the authoritative reference, and the market’s spread across multiple outcomes reflects exactly that seasonal uncertainty.

What makes NO real here is not a dramatic weather event. The barrier is simply that a specific single-degree outcome in a band of plausible temperatures is unlikely to be the exact reading. If the overnight low falls at 20°C or 22°C instead of 21°C, the 21°C contract expires worthless regardless of how close the temperature came. Exactness is the obstacle, not direction.

• China Meteorological Administration forecast updates: Any revision to the May 20 overnight low projection would reprice competing outcomes immediately.
• Regional synoptic pattern: A shift in the position of the East Asian jet stream or a frontal system approaching the Yangtze Delta could push lows below 19°C or above 23°C, collapsing probability toward the tails.
• Model consensus tightening: If multiple forecast models align on a specific temperature in the next 12 hours, the leading outcome gains and all others compress.
• Official station data at resolution: Polymarket’s resolution will rely on a specific observational record. Which station and which reading matters.

The $1,486 in total volume means this contract reflects a handful of traders making narrow temperature calls, not broad market conviction. The data favors the NO side simply because 21°C is one outcome among many plausible ones. The market is pricing uncertainty, not science.

LINES VERDICT

Thin Market, Long-Shot Temperature Call

The 21°C outcome is trading as a minority position in a multi-way temperature market with less than 24 hours to resolution. With no momentum, dormant volume, and a spread of competing outcomes all drawing capital away from this specific reading, the NO side reflects the basic math of single-degree exactness in a variable climate system.

What the market says: 24.5% probability means traders see this as a real but unlikely outcome. With resolution at 2026-05-20 12:00:00, any late forecast revision or model shift in the next several hours could reprice this contract sharply given how thin the liquidity is.

Key unknown: The China Meteorological Administration’s final overnight low forecast for Shanghai on May 20 is the single data point that would most move this contract. A forecast landing firmly at 21°C would push YES higher. Anything else pulls capital toward competing outcomes.

Scientific Context

Shanghai’s May overnight lows average around 19°C to 21°C based on historical climatological records, with meaningful year-to-year variability driven by the East Asian monsoon’s advance timing. In warmer-than-average spring years, the monsoon front pushes northward earlier, lifting overnight minima. In cooler years, persistent northerly flow keeps lows suppressed into the high teens. May 2026 sits within the climatological window where either scenario is plausible, which is exactly why the market has spread probability across outcomes from 15°C or below to 25°C or higher. The 21°C outcome is within the historical mode, which is why it carries a non-trivial 24.5% probability rather than sitting near zero. But historical frequency alone does not make it the most likely single outcome when competing temperatures each draw their own probability mass.

FAQ

• What does 24.5% probability mean here? It means traders estimate roughly a one-in-four chance that Shanghai’s official overnight low on May 20 lands exactly at 21°C. Probability reflects collective trader judgment, not a scientific forecast.
• What does the NO contract pay out? If the May 20 overnight low in Shanghai is any temperature other than 21°C, the NO position on this specific outcome pays. The NO price of 0.76 reflects 75.5% probability of that happening.
• What data would move this price the most? An updated China Meteorological Administration forecast showing the overnight low locked in at or near 21°C would push YES higher. A forecast diverging from that target would compress it further.
• When does this contract resolve? Resolution is set for 2026-05-20 12:00:00. With less than 24 hours remaining, the window for price movement is narrow but still open while overnight temperatures are still forecast rather than observed.
• Is $1,486 in volume enough to trust the price? Volume this thin means the price can move sharply on a single trade. $12,361 in liquidity provides some buffer, but this is a low-activity market where the implied probability should be treated as directional, not precise.

This analysis reflects market conditions as of 2026-05-19 08:24:26. Prediction market probabilities are volatile and shift as new data and regulatory decisions emerge, especially as the 2026-05-20 12:00:00 resolution date approaches. Lines.com does not accept bets or provide financial or gambling advice. All market outcomes are uncertain.