The closely matched probabilities for Tokyo's May 20 minimum temperature reflect high forecast uncertainty from variable springtime circulation patterns over the western Pacific. Ensemble models show potential for either a cool northeasterly flow maintaining readings near 18°C or gradual warming under building high pressure that could push lows to 20–21°C. Historical mid-May climatology places typical overnight minima around 16–19°C, but recent sea-surface temperature anomalies and jet-stream positioning introduce notable model spread. Traders are weighting the risk of brief frontal passages versus stable subtropical air, with resolution hinging on the final 48-hour forecast issued by the Japan Meteorological Agency.