**The overwhelming 99.9% market-implied probability for a 54–55°F low in Seattle on September 13, 2026, rests on official National Weather Service observations from standard stations such as Seattle-Tacoma International Airport.** Multiple real-time reports and preliminary climatological summaries recorded a minimum in that narrow range amid mild, cloudy conditions with southerly flow and light showers, consistent with late-summer norms where average lows sit near 53°F. This skin-in-the-game consensus reflects traders incorporating verified thermometer readings rather than forecasts. Only an official data revision or station-specific discrepancy could realistically alter the outcome, both of which carry negligible probability given the tight clustering of reports.