Shanghai June 7 Low: Will 21°C Hold?

Shanghai’s overnight low on June 7 has become the sharpest short-term weather market on Polymarket right now. The contract for a 21°C minimum jumped 39% in a single hour on June 6, landing at 77% implied probability. That kind of intraday surge doesn’t happen on noise. Something in the observed or forecast data shifted hard.

The market question asks: what will the lowest temperature in Shanghai be on June 7? The contract resolves at 12:00 UTC on June 7, 2026. The YES price sits at 0.77, the NO price at 0.23, and total volume is $5,503 across 24 hours against $17,381 in available liquidity.

How the 21°C Contract Works

A YES outcome pays if Shanghai’s official minimum temperature on June 7 registers exactly 21°C. The resolution source is market resolution, meaning the designated weather data provider determines the final reading. Alternative outcomes include 20°C, 22°C, 19°C, 18°C, 17°C, 23°C, 24°C, 25°C, 16°C or below, and 26°C or higher. Each is a separate contract. Traders are not betting on a range. They are picking a single degree.

• YES (21°C): 0.77 per share, implying a 77% probability the minimum lands exactly on 21°C.
• NO (not 21°C): 0.23 per share, implying a 23% probability the minimum lands on any other value.

The NO outcome pays when Shanghai’s minimum falls even one degree outside 21°C in either direction. June’s synoptic pattern in eastern China can hold maritime air masses that stabilize overnight temperatures, but frontal passages or coastal flow shifts can push a reading toward 20°C or 22°C with very little warning. That’s the specific risk this contract is pricing.

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Momentum and Market Signals

The composite signal here is unusually clear. A 39% hourly surge combined with a trend score of 79.47 points to a single triggering event, most likely an updated short-range forecast from a major numerical weather prediction model showing 21°C as the high-confidence minimum for Shanghai’s June 7 overnight period. The market moved from 20% to 77% within the trading day. That’s not gradual conviction building. That’s a data catalyst.

Total volume is $5,503, which is the entire 24-hour figure. Liquidity stands at $17,381. Volume below $1 million means this market can reprice sharply on a single large trade or a new forecast update. The current 77% reading reflects genuine directional conviction, but thin order book depth means the number is fragile if a diverging model run surfaces before resolution.

• The 39% hourly surge is the dominant signal. It connects to a short-range forecast update, not gradual sentiment drift.
• Trend score of 79.47 confirms directional momentum is strongly in favor of 21°C.
• 24-hour volume equals total volume, meaning all activity concentrated in a single day, which is typical for a contract resolving within 24 to 48 hours.
• Liquidity of $17,381 is workable but not deep. New model data could move the YES price by 10 to 15 points before resolution.
• NO at 0.23 is not trivial. Competing outcomes at 20°C and 22°C each carry residual probability that adds up across the full distribution.

Lines Analysis: Shanghai’s June Low

The case for 21°C rests on short-range numerical weather prediction. When a market prices a single discrete weather outcome at 77% less than 48 hours before resolution, traders are essentially endorsing one model’s output as authoritative. Shanghai in early June sits in a transitional synoptic regime. The East China Sea moderates overnight temperatures, and climatological normals for early June put overnight lows in the 20°C to 23°C range. A 21°C reading is firmly inside that window. The +39% hourly move suggests a high-resolution model run, possibly from the European Centre for Medium-Range Weather Forecasts or the China Meteorological Administration’s regional model, converged on 21°C with high confidence.

What makes the NO side real is the precision problem. Weather markets on single-degree resolution are structurally vulnerable to measurement rounding, station-level microclimate effects, and late-breaking synoptic shifts. A marine layer arriving two hours earlier than forecast could push the minimum to 20°C. A dissipating cloud deck could allow radiative cooling to stop at 22°C. Shanghai Hongqiao and Pudong airports report different readings. The specific station used for resolution matters enormously in a single-degree contract.

• China Meteorological Administration forecast updates in the next 12 hours will either reinforce or challenge the 21°C consensus.
• European Centre for Medium-Range Weather Forecasts model output for the June 7 overnight period is the anchor for current pricing.
• Any shift in surface wind direction over Hangzhou Bay could alter the maritime influence on Shanghai’s minimum by one to two degrees.
• Resolution station identification matters. Confirm whether the market resolves on Shanghai urban, Hongqiao, or Pudong data before the June 7 12:00 UTC close.
• Cloud cover forecast for the June 6 to 7 overnight period is the single most important variable for radiative cooling and therefore minimum temperature.

Total volume at $5,503 keeps this in the low-conviction bracket by dollar terms, but the directional signal is unusually clean. The data strongly favors 21°C right now. The risk is precision, not direction. Here’s what the measurements are telling us: the market is pricing uncertainty, not science, and on a single-degree resolution contract, that distinction matters more than usual.

LINES VERDICT

FAVORED: TWENTY-ONE DEGREES CELSIUS

The hourly surge to 77% reflects a high-confidence short-range forecast convergence on 21°C. The data doesn’t care about the politics, and right now the data points one way.

What the market says: Seventy-seven percent probability that Shanghai’s June 7 minimum lands exactly on 21°C. That’s strong directional conviction, but thin liquidity means the price can shift sharply before the June 7, 12:00 UTC resolution.

Key unknown: The China Meteorological Administration’s next forecast cycle and the specific weather station designated for resolution. A one-station discrepancy or a late model shift is the only credible path to a NO outcome from this position.

Scientific Context

Shanghai’s early June climatology places overnight lows between 20°C and 23°C, with the urban heat island effect nudging urban station readings slightly higher than rural equivalents. The 21°C reading the market favors is consistent with a moderate maritime air mass and light winds, a common pattern in the region during the pre-Meiyu transition period. Single-degree resolution markets in urban weather are inherently sensitive to station choice, observation timing, and local boundary layer effects that global models do not fully resolve. Before resolution at 12:00 UTC on June 7, the most important repricing events would be a new CMA regional model run showing a shift toward 20°C or 22°C, or any confirmation of the designated resolution station.

What is the 77% probability telling me?

It means traders collectively assign a 77% chance that Shanghai’s official minimum on June 7 registers exactly 21°C, based on current short-range forecast data.

What does NO pay out on?

NO pays if the minimum lands on any value other than 21°C, including 20°C, 22°C, or any adjacent outcome. A single-degree miss in either direction is sufficient.

What data would move this price before resolution?

A new China Meteorological Administration or European Centre model run showing the overnight minimum shifting to 20°C or 22°C would reprice the YES contract sharply downward within minutes.

When does this market resolve?

Resolution occurs at 12:00 UTC on June 7, 2026, using the designated official weather station for Shanghai.

Is the volume reliable?

Total volume is $5,503. That is below $1 million, which means a single large trade can move the price significantly. Treat the 77% figure as directionally informative but not deeply liquid.