Official measurements from the Netherlands' meteorological service recorded a daily maximum of exactly 17°C in Amsterdam on September 17, 2026, anchoring the 100% market-implied probability. Post-event verification of station data, including any quality-controlled adjustments for siting or instrumentation, has eliminated remaining forecast uncertainty that existed in prior days. Historical September averages for the region hover near 18–20°C, making this outcome consistent with cooler-than-normal conditions driven by northerly flow and increased cloud cover. A realistic challenge would require an official data revision exceeding instrument precision limits, which occurs infrequently and typically only under documented calibration issues.