**Current forecasts for Mexico City on September 15, 2026, point to a nighttime low near 13–15°C (roughly 55–59°F), aligning with the market's strong 87.5% implied probability on 13°C.** Mexico City's high elevation of about 2,240 meters produces radiational cooling after sunset, but persistent cloud cover, high humidity from the rainy season, and light winds typically limit how far temperatures drop. Recent model runs and observations show partly cloudy to overcast skies with scattered showers or drizzle possible overnight. These conditions trap heat near the surface and prevent the sharper drops seen under clear, dry air. Official guidance and station data indicate the mercury will likely bottom out in the 13–14°C range around dawn, consistent with climatological September lows that average near 10–12°C but trend milder under current moist, stable patterns. Lower outcomes such as 7–8°C or 6°C or below carry roughly 50% or lower odds because they would require unusually clear skies, stronger northerly flow, or an unseasonal cold surge—none of which appear in the latest guidance. Higher readings above 13–14°C are discounted as the diurnal cooling cycle and elevation favor a drop into the mid-teens Celsius. Traders are pricing the consensus forecast tightly around 13°C, with limited room for surprise unless a late model shift or clearer-than-expected skies materializes before dawn.