Mexico City sits at 2,250 meters elevation with a temperate climate naturally moderated by its high altitude. May is late spring in the Northern Hemisphere, bringing warming trends across Mexico and historically reliable solar heating. This prediction market asks whether the highest temperature on May 18, 2026 will be exactly 21°C. Current YES odds of 2% indicate traders see this outcome as highly improbable, and for good reason. First, Mexico City's typical May highs range from 24–27°C, so 21°C would represent a notably cool day for the season—well below the seasonal normal. Second, hitting an exact single-degree threshold is inherently difficult; a high of 20°C or 22°C would both resolve NO, leaving traders with an extremely narrow band for YES resolution. The market resolves based on the official highest temperature recorded by Mexico's meteorological service for that calendar date. The 98% implied NO probability reflects both the strong climatological expectation for warmer May weather and the mathematical precision required to match exactly one degree. Unexpected weather disturbances like cold fronts or afternoon thunderstorms could theoretically suppress temperatures, but the dominant May pattern typically delivers plenty of solar heating.
What factors could move this market?
Mexico City's subtropical highland climate is fundamentally defined by elevation rather than latitude alone. At 2,250 meters above sea level, the city maintains moderate temperatures year-round compared to the tropical lowlands surrounding it. May represents the tail end of the dry season transitioning into the onset of the summer monsoon—a period when mornings can be refreshingly cool due to thin mountain air, but afternoons typically see robust heating from intense high-altitude sun exposure. The 2% odds for exactly 21°C on May 18 reflect profound trader skepticism about hitting this specific threshold. Several factors could theoretically push temperatures toward YES resolution. A well-timed cold front pushing south from the northern United States—relatively rare in May but not impossible—could suppress the daily high. Unusually heavy cloud cover or a major afternoon thunderstorm system (early monsoon activity) could limit solar heating and keep the high depressed. A lingering cool air mass or a stalled weather system overhead could theoretically deliver suppressed conditions. However, historical and climatological data consistently show such scenarios are uncommon during May in Mexico City; the seasonal pattern is robustly warm with highs reliably clustering in the 24-27°C band. Conversely, factors pushing toward NO (the 98% market consensus) are far more climatologically dominant. Normal May weather in Mexico City delivers clear, dry mornings, building cumulus clouds in the afternoon, but strong solar heating at altitude that routinely pushes highs well into the mid-to-upper 20s. A particularly warm May pattern—entirely plausible given decadal climate trends and natural variability—could push highs toward 28-30°C, rendering a 21°C outcome mathematically impossible. Even a marginally above-normal day would miss the narrow 21°C target. Historically, May in Mexico City rarely produces highs below 22°C. The elevation moderates temperature extremes but the month's astronomical position and incoming monsoon energy typically ensure strong daytime heating. Weather station records from the past decade show May highs consistently in the 24-27°C range, with outlier cool days extremely rare. The current 2% odds reflect rational pricing: traders assess roughly 1-in-50 probability that May 18's official high lands exactly on 21°C, accounting for both climatological norms and the measurement precision required. The spread also suggests confident consensus rather than dispute. No traders are aggressively betting on YES; market liquidity is modest and volume nil, indicating the outcome is widely seen as unlikely rather than contested. This uniform conviction supports the 2%/98% split as a fair reflection of true probability.
What are traders watching for?
Official Mexico City weather observation on May 18—market resolves at midnight UTC based on highest temperature recorded by the national meteorological service
Cold front activity from the north or early monsoon system—atmospheric disturbances that could theoretically suppress daily highs below seasonal norms
Afternoon thunderstorm occurrence—convective activity triggered by monsoon onset that could limit solar heating and cloud cover the region
Historical May pattern persistence—normal warm-weather continuation would likely keep highs in the 24-27°C range, missing the 21°C threshold
How does this market resolve?
Market resolves YES if Mexico City's official highest recorded temperature on May 18, 2026 is exactly 21°C; otherwise resolves NO. Resolution is based on the official reading from Mexico's meteorological service at midnight UTC on May 18.
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.
