Trade: Highest temperature in London on May 9?

Market context

On 9 May 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The market resolves based on data from Weather Underground's historical records for that specific station, with settlement occurring at midday on the day itself. Currently, Polymarket's order book shows 0% implied probability across all temperature brackets, indicating minimal trading activity or a technical lag in probability aggregation rather than genuine consensus that no temperature will be recorded.

London's May temperatures typically range between 12°C and 20°C, though outliers occur regularly. Historical data from the Met Office shows that May highs in central London have reached 28°C (2008) and 27°C (2015), whilst cooler years have seen maxima around 15°C. The 30-year average high for early May sits near 18°C. City Airport's location in East London, closer to the Thames estuary, can produce marginally different readings from central London due to urban heat island effects and proximity to water, though differences are typically modest.

Traders should monitor the extended forecast as May 2026 approaches, particularly Atlantic weather patterns that drive UK temperatures. High-pressure systems moving north from the continent typically produce the warmest May days, whilst Atlantic low-pressure systems keep temperatures suppressed. The UK Met Office issues detailed 10-day forecasts roughly a week before the settlement date, providing the most actionable catalyst for position adjustments. Current order book inactivity suggests limited liquidity, which may widen spreads significantly once forecasts crystallise.

Resolution source

This market settles from the official outcome published at https://www.wunderground.com/history/daily/gb/london/EGLC. A proposer submits the final result to the UMA optimistic oracle on Polygon; the two-hour dispute window closes and payouts clear in USDC.

How to trade this market step by step

The mechanics for trading "Highest temperature in London on May 9?" are the same as any other PolyGram event contract. Each YES share resolves to $1 if the event happens, or $0 if it doesn't. The current price between 0¢ and 100¢ is the market's probability estimate, set live by the order book.

1. Sign in on polygram.ink with your email — no full KYC under $1,500 lifetime trading volume.
2. Deposit USDC on Polygon (lowest fees, ~$0.01 per transaction) or Ethereum. Funds credit after 12 confirmations.
3. Pick a side. Buy YES if you believe the event will happen; buy NO if you think it won't. The current YES price reflects the market's collective probability.
4. Size your position. If you stake 100 USDC at 50% YES, you'll receive shares that pay $200 if YES resolves true — a 100% gross return. If NO resolves, your shares are worth $0.
5. Set risk controls (optional). Stop-loss, take-profit, and limit-order types all supported. Use the trade ticket's slippage box to cap your maximum entry price.
6. Wait for resolution. When the event resolves on-chain via the UMA optimistic oracle, the winning side settles to 100¢ automatically and USDC hits your balance within seconds. Withdrawable to any wallet you control.

How active is this market?

$169K in lifetime turnover and $57K of resting liquidity puts this market in the top 30% by volume for weather contracts on PolyGram. Order-book depth is exceptional — among the deepest order books in the category.

Last 24 hours alone saw $114K in turnover, well above the lifetime daily-average for this market — a clear sign of news catalysing trader activity right now.

The market has been open for under a month — fresh enough that information asymmetry remains a real factor.

Higher-volume markets tend to have tighter spreads and faster price discovery — meaning the displayed YES/NO percentages are more likely to reflect the true crowd-implied probability rather than a single trader's directional view.

Key terms

YES / NO share

A binary outcome token that pays $1.00 if the underlying claim resolves true (YES) or false (NO), and $0 otherwise. The market price between 0¢ and 100¢ is the implied probability.

CLOB

Central limit order book. The matching engine that pairs YES buyers with NO buyers (effectively the same trade). Polymarket's CLOB on Polygon executes trades on-chain via the conditional-tokens framework.

Liquidity

USDC capital sitting in resting limit orders inside the order book. Deeper liquidity means smaller slippage on large trades and a tighter bid-ask spread.

UMA optimistic oracle

The on-chain dispute system that settles each Polymarket market. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution.

Slippage

The difference between the displayed mid-price and your fill price. Affects market orders most; limit orders avoid slippage but may take time to fill.

Conditional token

ERC-1155 outcome share issued by Gnosis Conditional Tokens on Polygon. The token type that resolves to $1.00 or $0.00 at settlement.

See the full prediction-market glossary →

Frequently asked questions

Risk and regulatory note

Prediction-market positions can lose 100% of staked capital. Outcomes are uncertain by definition — historical accuracy of crowd-implied probabilities is high in aggregate but not for any single market. PolyGram does not provide investment advice. Trade only with capital you can afford to lose.

Regulatory status varies by jurisdiction. Germany, the United States, and most EU countries treat Polymarket-style event contracts under one of three frameworks: financial derivative, gambling product, or unregulated novel asset. Consult local counsel before trading.

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