San Francisco's May weather typically brings mild temperatures in the low to mid-60s Fahrenheit, with daytime highs frequently driven by marine layer strength and inland heating patterns. A high of 58-59°F represents the cooler end of the spring spectrum for the Bay Area, requiring either persistent marine layer influence or an unusual cold air mass. The market resolves based on the National Weather Service's official high temperature reading for San Francisco on May 19, 2026. At just 1% odds for YES, traders are signaling low conviction that temperatures will cool this much. Such narrow, cool temperature bands are climatologically rare in May but not impossible—persistent fog and cloud cover can suppress highs into the upper 50s. The extremely low probability reflects typical late-spring patterns where high pressure systems and increasing daylight hours drive temperatures into the 60s or higher.
Deep dive — what moves this market
San Francisco's unique microclimate during May is shaped by the interaction between the Pacific Ocean's cool waters and the peninsula's geography. Sitting on three sides of water, the city experiences frequent marine layers—cool, moist air masses—that can persist through afternoon hours, especially when atmospheric conditions favor marine inversion. A high of 58-59°F would require either a strong marine layer lasting through peak heating hours or an unusual cold air mass moving down the Pacific coast. Historically, such cool, narrow temperature ranges are far more common in June, when the summer fog season intensifies, than in mid-May when solar heating increases dramatically. What could push this market toward YES? A deep upper-level low-pressure system tracking along the West Coast could funnel cool Pacific air inland and suppress afternoon highs. Persistent northeast or north winds would reinforce marine layer conditions and prevent inland heating. Night-time lows in the upper 40s would signal a cooler atmospheric pattern extending into daytime hours. What pushes it toward NO? High pressure building over the Pacific drives typical warming trends. Clear skies and light winds allow inland areas and even coastal zones to warm significantly in May. With each passing day in mid-May, longer daylight hours provide more solar heating potential. Climate normals show San Francisco's May average high around 62-64°F, well above this narrow 58-59°F band; even modest deviations toward normal conditions trigger NO resolution. Recent precedent strongly supports the 1% odds: San Francisco rarely experiences such cool, precisely constrained highs after mid-May. Most weather forecasts in May target ranges of 60-65°F or higher. Traders pricing this at 1% reflect deep confidence in typical spring warming patterns prevailing over any localized marine layer effects.
What traders watch for
NOAA/NWS forecast for May 19 released May 17-18; watch marine layer persistence outlook
May 18-19 overnight lows; cool mornings signal whether daytime highs will remain suppressed
Cloud cover and fog intensity on May 19; persistent marine layer blocks afternoon solar heating
Pacific high pressure system positioning; strong highs mean warmer, sunnier conditions in Bay Area
How does this market resolve?
Market resolves based on the National Weather Service official high temperature for San Francisco on May 19, 2026. YES if the highest temperature is between 58-59°F (inclusive); NO otherwise.
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.
