San Francisco's weather on May 18 is rapidly approaching resolution clarity as the date arrives within 48 hours. Current YES odds of 2% reflect extremely low trader confidence that the high temperature will fall within this narrow 60-61°F window. Historically, San Francisco's May temperatures typically range from 58-70°F, making a precisely bounded 1-degree range statistically unlikely. The market suggests traders assess higher probability for either cooler (below 60°F) or warmer (above 61°F) outcomes. This narrow band represents only about 5-10% of the typical May temperature distribution for the Bay Area. The low liquidity ($1,197) and zero 24-hour volume indicate minimal trader activity, typical for these hyperspecific daily weather markets. With resolution imminent, the National Weather Service forecast serves as the primary reference point—current outlooks would need to call for a high of exactly 60-61°F for YES positions to gain traction. The market essentially prices in the statistical improbability of such precise alignment between forecast and observation.
Deep dive — what moves this market
San Francisco's temperate Mediterranean-influenced climate creates relatively stable weather patterns, particularly in May as summer approaches. The city's unique geography—surrounded by the Pacific Ocean and positioned between the Bay and coastal ridges—moderates temperature swings year-round. Historical May data shows San Francisco highs cluster between 58-72°F, with an average high around 67°F. The narrow 60-61°F band represents only a small statistical tail of this distribution, explaining both the 2% odds and minimal trading activity. Weather prediction markets thrive on the intersection of atmospheric science and probability. The National Weather Service updates its May 18 forecast continuously as new satellite, radar, and model data arrives. Current projections suggest typical spring conditions for the Bay Area, though forecasters typically predict temperature ranges (e.g., "high 62-68°F") rather than single-degree precision, creating inherent structural mismatch between market granularity and real-world meteorological forecasting practice. This granularity gap reinforces low confidence among traders. Several factors could push the May 18 high toward the 60-61°F window. A marine layer holdover—the low stratus and fog common in San Francisco spring—could suppress afternoon heating. Coastal winds and onshore flow from a Pacific system could confine temperatures to the upper 50s and low 60s. Persistent overcast skies and reduced solar insolation would further limit warming potential. Conversely, factors pushing temperatures above 61°F include high pressure inland forcing dry, warmer air westward; clear-sky afternoon heating; or reduced ocean influence from wind patterns favoring warmer interior air masses. Outcomes below 60°F become less likely by mid-May statistically, though remain possible with unusual cold-air intrusion. Historical May 18 data shows substantial year-to-year variability, with recorded highs ranging from 58°F to 72°F. This historical spread directly reinforces the 2% odds—the market must price in inherent uncertainty and the rarity of any single narrow band aligning precisely with actual observation. Trader conviction, reflected in both low odds and minimal volume, suggests near-consensus skepticism. The illiquidity and zero 24-hour volume indicate limited capital committed to what most traders perceive as an extreme long shot, consistent with statistical reality.
What traders watch for
National Weather Service May 18 forecast: track updates from today through close; any range below 60°F or above 61°F invalidates YES.
Marine layer / coastal fog strength May 18 morning: if fog burns off fully, afternoon temps likely exceed 61°F; persistent layer suppresses heat.
High-pressure system location: inland ridge intensifies above 61°F outcomes; marine-influenced trough favors the narrow 60-61°F window.
Official SFOB temperature reading May 18: high must land exactly between 60.0°F and 61.0°F inclusive at San Francisco International Airport station.
How does this market resolve?
This market resolves YES if the highest temperature recorded at San Francisco's official weather station (SFOB, San Francisco International Airport) on May 18, 2026, falls between 60.0°F and 61.0°F inclusive. Resolution is based on National Weather Service official daily maximum temperature observation.
Prediction markets aggregate trader expectations into real-time probability estimates. On Polymarket Trade, 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. This page summarizes the market state for readers arriving from search; for live trading (place orders, see order book depth, execute a trade) open the full interactive page linked above.
