Shanghai May 31 Low Temperature: Will It Hit 18°C?

The market has already priced this as settled. A massive 62-point swing in 24 hours pushed the 18°C outcome to 98.4% implied probability, and the momentum composite shows no sign of reversal. Traders aren’t weighing options here. They’re converging on a single meteorological conclusion: Shanghai’s lowest temperature on May 31 will land at exactly 18°C.

The market question asks which value the lowest temperature in Shanghai will reach on May 31. The 18°C outcome trades at $0.98 YES and $0.02 NO, resolving at noon UTC on May 31, 2026. Total volume sits at $13,635, with $12,938 of that flowing in the last 24 hours alone.

How the 18°C Contract Works

This contract resolves YES if the verified lowest temperature in Shanghai on May 31 registers at 18°C according to the resolution source. All other outcomes, including 17°C, 19°C, and the dozen other listed brackets, resolve NO. The contract closes at 12:00 UTC on May 31, 2026.

• YES ($0.98, 98.4% probability): Shanghai’s lowest temperature on May 31 measures exactly 18°C per the resolution source.
• NO ($0.02, 1.6% probability): The overnight low falls into any other bracket, including 17°C, 19°C, or any value above or below.

The NO outcome pays when the overnight low drifts even one degree outside the 18°C bracket. Shanghai’s late-May temperatures are typically in the 18°C to 22°C range for overnight lows, but short-term forecasts narrow or widen those bands daily. A cold front arriving earlier than modeled or a warm advection event persisting longer than expected could push the reading into a neighboring bracket. The resolution source determines the final number, so rounding conventions and measurement methodology matter at the margin.

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Momentum and Market Signals

The 1-hour and 24-hour price changes, combined with a trend score of 61.93, form a single strong bullish signal. The 62-point daily surge is the dominant driver, almost certainly reflecting updated short-range numerical weather prediction models aligning on 18°C as the most probable overnight low for May 31 in Shanghai.

Total volume is $13,635, with $12,938 arriving in the last 24 hours. Liquidity sits at $67,071, which is unusually deep for a short-duration weather contract at this volume level. That liquidity depth means the 98.4% price is not an artifact of a thin order book. Capital is genuinely committed to this outcome.

• The 24-hour volume surge of $12,938 against a total of $13,635 signals a sharp, recent consensus shift, not gradual drift.
• Liquidity of $67,071 far exceeds volume, meaning the order book can absorb new positions without significant price movement.
• The 1-hour price change is flat at 0.0%, suggesting the 98.4% level is a resting point, not an active climb.
• The trend score of 61.93 confirms sustained directional conviction over the measurement window.
• Related science markets on Polymarket show no unusual activity that would correlate with a Shanghai weather disruption.

Lines Analysis: Shanghai’s Overnight Low

Late May in Shanghai sits in the transition zone between spring and early summer. Synoptic patterns this time of year typically produce overnight lows in the 18°C to 21°C range. When numerical models, the kind that drive short-range forecast consensus, anchor on 18°C for May 31, traders follow. The 62-point price surge reflects exactly that kind of model convergence. The market isn’t guessing. It’s reading the forecast output and pricing accordingly.

The realistic path to NO runs through model error or a late-breaking weather system. Shanghai’s overnight low could dip to 17°C if a cold trough arrives slightly ahead of schedule. Alternatively, persistent warm southerly flow could hold the low at 19°C or higher. Both scenarios are meteorologically possible within 24 to 36 hours. Neither is currently reflected in the dominant forecast signal that drove the price to 98.4%.

• Short-range NWP model output for Shanghai on May 31 is the single most important signal. Any ensemble spread widening toward 17°C or 19°C would erode the YES price.
• Shanghai Meteorological Service observations through the evening of May 30 will set the baseline temperature trend heading into the overnight window.
• Any significant frontal boundary movement over the Yangtze Delta in the next 18 hours could shift the forecast bracket.
• Resolution source methodology matters: the exact reporting station and time window used to determine the official low temperature directly determines YES or NO.
• Flat 1-hour momentum at 98.4% suggests the market is waiting for May 31 observations to confirm, not for new forecast information.

Total volume of $13,635 is modest for a prediction market, but the $67,071 liquidity pool and the concentration of volume in the last 24 hours tell a clear story. The data favors 18°C. The market has priced it near certainty. The only variable left is whether the atmosphere cooperates with the forecast.

LINES VERDICT

HIGH CONFIDENCE: EIGHTEEN DEGREES

The market has converged decisively on 18°C, driven by a 62-point 24-hour surge and deep liquidity that validates the price. Short-range forecast alignment is the engine here, and the flat 1-hour momentum confirms the market is done moving until May 31 observations arrive.

What the market says: At 98.4% implied probability, the market has priced 18°C as nearly certain. That level of conviction is warranted when forecast models align this tightly this close to resolution. With less than 24 hours to the May 31 noon UTC close, volatility risk is real but narrow: a one-degree forecast miss in either direction is the only credible repricing event.

Key unknown: The resolution source’s official low temperature reading for Shanghai on May 31 is the single deciding factor. If the verified overnight minimum registers at 17°C or 19°C rather than 18°C, the entire probability collapses to zero regardless of how close the reading is.