San Francisco's weather on May 18, 2026 is a measurable, verifiable event subject to official NOAA observation. This prediction market asks whether the city's peak daily temperature will fall within an unusually narrow band: exactly 56°F to 57°F. The current prediction market odds of 1% for YES reflect traders' conviction that hitting this specific temperature range is extremely unlikely. May typically brings mild to warm conditions to the San Francisco Bay Area, with average highs in the mid-60s and average lows around 55°F, driven by maritime influence from the Pacific Ocean. The 56-57°F range represents cooler-than-typical conditions for mid-May, potentially requiring marine layer dominance or an upper-level trough. The market will resolve using official NOAA data from San Francisco International Airport, the standard weather station for the city's official climate records. With only two days until expiration on May 18 at midnight UTC, traders have limited time to adjust positions based on incoming weather forecasts. The extremely low YES odds suggest strong market consensus that temperatures will either exceed 57°F or fall below 56°F. This is a hyperspecific weather prediction—the narrower the target range, the lower the probability.
What factors could move this market?
San Francisco's climate is heavily influenced by the Pacific Ocean and the Bay's unique geography, creating a relatively temperate and stable environment compared to inland California. The city rarely experiences extreme temperatures; even in summer, highs typically stay in the 60s-70s due to persistent marine cooling. May is a transitional season, hovering between spring and early summer, with average highs around 65°F and average lows around 55°F. The specific target of 56-57°F would represent below-average conditions—the kind that occurs during marine layer intrusions, upper-level troughs, or coastal storms pushing cool air onshore from the Pacific. For this market to resolve YES, a combination of weather patterns would need to align perfectly: persistent marine influence, significant cloud cover, and northern Pacific circulation patterns that prevent inland heating from solar radiation. This is plausible but statistically uncommon for mid-May in San Francisco. The NO scenario—temperatures above 57°F or below 56°F—is far more likely given typical spring and early summer conditions. High-pressure systems occasionally bring warmth to 75°F or higher, while rare intrusions of cold air from the north could push conditions into the 50-55°F range, missing the exact target band entirely. Historical data from NOAA shows that extreme specificity in daily temperature predictions (single-degree ranges) has very low success rates in practice; natural weather variability within even a 5-degree band is substantial day-to-day. Recent May records for San Francisco show significant day-to-day variation, with daily highs ranging from 58°F to 78°F depending on prevailing synoptic patterns and ocean conditions. The 1% market odds reflect this inherent unpredictability and the fundamental difficulty of precision forecasting three days into the future. The extremely tight liquidity and minimal trading volume suggest this is a niche prediction market with little trader interest—possibly because most market participants view such narrow forecasts as essentially unpredictable rather than a skill-based analytical trade. Prediction markets typically attract meaningful volume when outcomes feel genuinely uncertain but potentially resolvable through careful research; hyperspecific temperature bands fall well outside that sweet spot.
What are traders watching for?
NOAA issues final temperature data for San Francisco International Airport weather station on May 19; reading determines market resolution.
Marine layer intensity on May 18 will be the primary driver; persistent fog and cloud cover essential to suppress temperatures below 57°F.
High-pressure system movements and northern Pacific jet stream position will determine whether conditions stay mild or dip below typical May levels.
Market expires May 18 at midnight UTC; traders have only 48 hours from market publication to position based on weather forecasts.
Temperature precision at this scale—one degree Fahrenheit—makes this a near-impossible short-term forecast; meteorological models typically accurate within ±3°F.
How does this market resolve?
Market resolves on May 19 using official NOAA data for San Francisco International Airport, with YES requiring the high temperature to fall between 56–57°F inclusive on May 18.
Polymarket Trade is an independent third-party interface to the Polymarket CLOB prediction market exchange on Polygon — not affiliated with Polymarket, Inc. Prediction markets aggregate trader expectations into real-time probability estimates. Every market question resolves YES or NO based on a specific event outcome; traders buy shares of the side they believe will resolve positively. Prices range 0¢ (certain no) to 100¢ (certain yes) and naturally reflect the crowd-implied probability of YES. Polymarket Trade is non-custodial — your funds never leave your wallet. Open the full interactive page linked above to place orders, see order book depth, and execute a trade.
