This market tracks whether Sao Paulo's daily high temperature will reach 25°C (77°F) on May 18, 2026. The event is straightforward to resolve using publicly available weather data from Brazil's National Institute of Meteorology (INMET). Currently priced at 1% YES odds, the market overwhelmingly expects the high to remain below 25°C. This pricing reflects typical autumn conditions in Sao Paulo during mid-May, when cooler weather patterns dominate the region. Sao Paulo's climate at this time of year typically sees highs in the 18–23°C range. The 1% odds suggest strong trader conviction that the temperature threshold will not be breached, grounded in seasonal climatology and historical precedent. Any upside surprise would require unseasonable warmth from tropical air masses or rare atmospheric systems.
What factors could move this market?
São Paulo, Brazil's largest metropolis and economic hub, experiences a subtropical climate with pronounced seasonal variations. In May, the city enters autumn (outono), marked by a transition from summer's warmth toward cooler, more stable conditions. Historically, May highs in São Paulo average between 19–24°C, with the 25°C threshold representing the boundary between typical cool-season weather and anomalously warm conditions. Reaching 25°C+ in mid-May occurs in only a small percentage of years and would indicate either an extended heat wave or a rare tropical incursion. Factors that could push toward YES include: an upper-level ridge pattern stalling over southeastern Brazil, allowing heat accumulation; equatorial tropical air masses extending southward with unusual vigor; a delayed or weakened cold front progression; or localized urban heat island intensification. These scenarios are plausible but statistically uncommon for May. Factors supporting NO (below 25°C) are far more dominant: the typical May pattern features regular southeastward cold front passages from higher latitudes, bringing cooler air masses; the Southern Hemisphere autumn is characterized by declining thermal energy; 30+ years of meteorological records show temperatures below 25°C on roughly 85–90% of May days; and contemporary climate models generally predict near-normal or slightly cool conditions for mid-May 2026. Historical precedent from recent Mays shows scattered warm days occasionally exceed 25°C, but these are outliers. The 1% odds reflect this stark asymmetry in probabilities, encoding high confidence that seasonal patterns will prevail over anomalous conditions.
What are traders watching for?
May 18 official high: Verify temperature from INMET or a recognized meteorological source; must reach exactly 25°C or higher.
Multi-day forecast evolution: Monitor weather model updates 7–3 days prior to watch for any developing warm anomalies or tropical systems.
Cold front timing: Track whether a cold front passage occurs on May 18 or nearby, as this would reinforce below-25°C conditions.
Historical analog: Review May 2019 and May 2021 data for Sao Paulo highs to assess how often 25°C+ actually occurs in this month.
How does this market resolve?
The market resolves YES if Sao Paulo's official daily maximum temperature on May 18, 2026 reaches 25°C or higher according to INMET. It resolves NO if the high is below 25°C.
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.
