San Francisco weather in mid-May is typically temperate, ranging from low-50s to mid-60s. A high of 58-59°F would be unusually cool for May in the Bay Area, suggesting strong coastal marine influence or a weather system bringing cooler air from the Pacific. The current 2% YES odds imply traders see this as a low-probability event, suggesting consensus expects warmer conditions typical for mid-May. Historical May data for SF shows average highs around 65-70°F, making the 58-59°F range a significant departure from seasonal norms. This narrow temperature band is highly specific—a precise 2-degree window—which increases difficulty in prediction. The market resolves based on the official recorded high temperature at the San Francisco weather station. Low trading volume and 2% odds suggest minimal market interest, likely because the specificity and tight range make it an unattractive trade. Weather forecast data becomes more reliable closer to May 18, creating potential for sharp odds movement if meteorologists signal unusual coolness or marine layer strength approaching the Bay Area.
What factors could move this market?
San Francisco's weather during May is shaped by the strength of the Pacific high-pressure system and coastal marine layer. In typical years, a sustained marine layer keeps the city's highs in the low-to-mid 60s, while clear inland conditions can push peaks toward 70°F. For the high to land at 58-59°F—below even typical marine-dominated days—requires an unusually strong cold marine layer, a low-pressure system bringing anomalous coolness, or remnants of a coastal storm system. Historically, May in San Francisco rarely sees single-day highs as cold as 58-59°F; such temperatures are more typical of February or early March. A review of recent May weather shows this range occurs perhaps once or twice per decade in the Bay Area, explaining the 2% implied probability. Several factors could push the market toward YES: a coastal storm system or low-pressure trough moving through Northern California would dramatically cool temperatures, a particularly strong marine layer event where fog and cool ocean air dominate throughout the day without warming inland could keep the high in the high 50s, and sustained northwesterly winds from cool ocean sources would support this outcome. Conversely, factors pushing toward NO include the seasonal strengthening of the Pacific high-pressure system which typically brings warmer air by late May, a brief inland push or light offshore wind would likely push the high above 59°F, and cloud-free skies or light winds would allow inland heating warming the peak into the 60s. The 2% odds reflect a rational assessment of May climatology; the narrow 2-degree band increases difficulty requiring forecast precision, not just cooler-than-average readings. The low 24-hour volume and minimal liquidity suggest traders find this market low-information; the event is meteorologically unlikely and the narrow range makes conviction difficult to price. Extended weather forecasts and model consensus for May 15-18 will be key drivers. If forecast models show an unusual cool trough or sustained marine layer for May 18 by mid-May, odds could reprice sharply higher. Until then, the 2% reflects baseline climate expectation: San Francisco typically runs warmer than 58-59°F in May.
What are traders watching for?
National Weather Service extended forecast for May 18 SF high temperature; monitor signals of unusual coolness or marine layer strength.
Pacific high-pressure system positioning and intensity; watch for approaching low-pressure systems or coastal troughs May 16-18.
Marine layer forecast and coastal influence data; NOAA marine forecasts and fog advisories for May 17-18 are critical indicators.
Official KSFO weather station high temperature reading on May 18; settlement based on NOAA recorded data at day close.
How does this market resolve?
Resolves YES if the highest temperature recorded at San Francisco's official weather station on May 18, 2026 falls between 58–59°F inclusive. Resolves NO if the high is 57°F or lower, or 60°F or higher.
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