**The market's near-certain pricing on 20°C as the day's highest temperature reflects real-time meteorological observations confirming that peak.** Clear skies, southeasterly winds of 25–40 km/h, and stable high pressure around 1030 hPa allowed daytime warming to reach 20°C during the afternoon hours at Cape Town stations, consistent with model consensus from sources like the South African Weather Service and international forecasts. This outcome aligns with the day's climatological range for mid-September, where maxima typically fall between 17–21°C under similar conditions. Traders priced in the result once hourly data and official summaries locked in the exact threshold, leaving negligible room for other bins. A realistic challenge would require a post-event data revision from the primary reporting station or a redefinition of the measurement window, though such adjustments are rare once preliminary readings are verified.