Recent ensemble forecasts from the Japan Meteorological Agency indicate a mild overnight period over the Kanto Plain on May 19–20, with high pressure and light variable winds limiting radiative cooling and supporting minimum temperatures near 19–21 °C at Tokyo’s official stations. This pattern, typical for late-spring transitional flow, keeps the market’s leading 21 °C outcome at 25 % implied probability while allowing the 25 °C-or-higher bucket to hold 21.5 % amid slight warm-air advection risks. Model spread remains modest, yet small differences in low-level moisture or residual cloud cover can shift the recorded low by 1–2 °C, explaining the tight clustering of 18–22 °C contracts between 13 % and 19 %. Updated JMA guidance and international model runs scheduled for the next 48 hours will refine the final resolution range.