Tokyo's mid-May overnight minimum temperatures typically hover between 15°C and 19°C under variable high-pressure influence, and current ensemble guidance from the Japan Meteorological Agency shows tight clustering around 17–19°C for May 18. Light winds and partial clearing could enhance radiative cooling toward the lower end of that range, while any southerly flow off the Pacific or lingering cloud cover would favor the higher bins. With leading market-implied probabilities nearly even across 17°C, 18°C, and 19°C, traders are reflecting genuine short-range forecast spread rather than a single dominant signal; the next model runs and surface observations over the next 48 hours will likely narrow the range before official Japan Meteorological Agency data resolve the market.