Will San Francisco's high temperature on May 18, 2026 fall within the narrow 50-51°F range? This market represents a highly specific weather prediction directly tied to a single day's maximum temperature in a location that typically experiences mid-May highs around 65-70°F. A high of only 50-51°F would constitute unusually cold weather for late spring, potentially driven by factors such as an unusually strong offshore marine layer, cool ocean advection patterns, or anomalous atmospheric pressure systems moving through the region. The current 1% YES odds reflect market participants' collective assessment that such a narrow, cold outcome remains extremely unlikely given historical seasonal patterns and established climatological baselines. Market resolution hinges precisely on official NOAA or National Weather Service maximum temperature readings for San Francisco's primary weather observation station. The precision required is notably constraining — the outcome must fall within exactly this one-degree band rather than simply demonstrate cold weather generally. Seasonal climate data and historical meteorological records show that San Francisco temperatures in the 50-51°F range during May occur relatively infrequently across multiple decades of modern records. The tight two-day countdown to market close means weather forecast precision becomes increasingly critical, as updated atmospheric models will provide higher-confidence guidance as May 18 approaches.
What factors could move this market?
San Francisco's climate is shaped by its unique geography at the tip of a peninsula, surrounded by the Pacific Ocean on three sides, which creates a moderating maritime influence that keeps temperatures cooler than inland California throughout the year. Mid-May typically brings highs around 65-70°F, with the Pacific marine layer — a cool, moist air mass fed by upwelling and ocean temperatures — playing a significant daily role in temperature modulation. The prospect of a 50-51°F high would require exceptional atmospheric conditions: either an unusually strong cold front advecting into Northern California from the north, a particularly robust marine layer with minimal solar heating penetration, or an unusual upper-level low-pressure system configuration. Historically, San Francisco experiences such notably cold May days only occasionally; National Weather Service records show that May days with highs below 55°F occur roughly once every 5-10 years, making the specific 50-51°F band even rarer. Factors pushing toward YES odds would be forecast evidence of an approaching polar or continental cold front, unusual upper-level negative NAO patterns, or anomalous Atlantic/Pacific teleconnection signatures that drive cold advection. Factors strongly pushing toward NO are the region's inherent spring warming pattern, the rarity of persistent cold systems, and typical high-pressure ridging that tends to dominate May. The 1% odds assessment reflects baseline climatological probability—drawn from historical frequency data—weighted against the specific two-day forecast window and current meteorological setup. Weather prediction models (GFS, NAM, HRRR) become increasingly reliable 2-3 days out, so as May 18 approaches, traders will gain higher-confidence guidance. The extreme narrowness of this range distinguishes it from broader markets; hitting precisely 50-51°F is mathematically more difficult than predicting a band like 45-55°F. This illustrates a key principle in weather derivatives markets: specificity compounds both difficulty and odds.
What are traders watching for?
May 18 NOAA official high temperature reading for San Francisco — this single data point determines market resolution
GFS, NAM, and HRRR forecast models for May 17-18 — updated runs will reprice market as May 18 approaches
Presence and strength of Pacific marine layer and cool advection — key driver of below-normal May temperatures
Upper-level atmospheric pressure patterns and any cold fronts moving toward Northern California May 16-18 period
How does this market resolve?
Market resolves YES if San Francisco's official National Weather Service maximum temperature on May 18, 2026 falls between 50-51°F inclusive. Market resolves NO if the high is outside this range.
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.
