This market resolves based on the National Weather Service's official high temperature for San Francisco on May 18, 2026. The 1% YES odds reflect market conviction that this outcome is extremely unlikely—a one-degree target range in late spring represents unusually cool conditions for the Bay Area. At current prices, traders are pricing less than a 1-in-100 chance of this specific temperature band occurring. San Francisco's May climate typically sees highs ranging from the mid-60s to low-70s Fahrenheit, making a 54-55°F high notably cool. This type of micro-precise weather market appeals to traders interested in high-specificity outcomes and demonstrates the predictive efficiency of distributed odds-setting in meteorological forecasting. The extremely low odds suggest professional traders or weather-informed participants are highly confident warmer conditions will prevail on May 18.
What factors could move this market?
San Francisco's climate in May transitions toward summer as high-pressure systems build along the West Coast and the Pacific marine layer—cool, moist air from the ocean—gradually diminishes its afternoon influence. The Bay Area's typical May pattern sees highs climbing from the upper 50s in early May toward the low-to-mid 70s by month's end, a predictable progression tied to seasonal solar forcing and atmospheric circulation shifts. A 54-55°F high would represent a notably anomalous outcome, reflecting conditions that occur only during unusual meteorological configurations: sustained marine layer persistence well into afternoon, a rare spring low-pressure system tracking through Northern California, or jet-stream patterns directing cool air southward. Historically, such cool May days in San Francisco are infrequent, occurring perhaps once or twice per decade rather than annually, and recent years have shown May temperatures trending toward the mild-to-warm side. Factors that could push the market toward YES include an unusually stubborn marine layer fed by cooler-than-normal offshore water temperatures from the preceding winter, a trough of low pressure detouring warm air masses, or unusual cloud cover extending through late afternoon. Conversely, the dominant NO-ward pressure comes from standard seasonal climatology: May's lengthening days and northward-shifting high-pressure ridge normally warm interior California regions substantially, with marine clouds burning off by early afternoon and allowing full solar heating to drive highs well above 60°F. The market's 1% YES odds reflect accumulated confidence among participants—which may include meteorologists, climate traders, or weather-informed traders—that standard spring patterns are highly likely to override anomalous configurations. This pricing suggests early forecast consensus, climatological base rates, and recent trend analysis all converge on rejecting the cool-day scenario. Should forecast models shift dramatically in coming days toward an unusual cool pattern, odds would likely adjust upward. The extreme specificity of a one-degree range rather than a broader band demonstrates how distributed prediction markets aggregate meteorological expertise into granular probability estimates.
What are traders watching for?
National Weather Service May 18 forecast—any model shift toward marine layer persistence or cool patterns could compress 1% odds significantly.
Marine layer burn-off timing on May 18 morning—earlier dissipation favors warmer highs; afternoon cloud persistence increases cool outcome probability.
Upper-level ridge and high-pressure positioning—if system locks in firmly, warmth dominates; southern trough dip enables marine influence to linger.
Historical May cool-day frequency in San Francisco—check recent records for 54-55°F highs; trend data shapes baseline probability assumptions.
How does this market resolve?
Market resolves YES on May 18, 2026, if the National Weather Service records a high temperature of 54°F or 55°F for San Francisco; otherwise resolves NO. Resolution uses official NWS data published for that date.
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.
