Current ensemble forecasts from the Japan Meteorological Agency and global models show substantial spread in Tokyo's overnight minimum for May 20, with projected lows ranging from roughly 14–22 °C due to uncertainty in the positioning of the Pacific subtropical ridge and potential weak frontal passages. May's transitional spring regime normally features average minima near 14–16 °C, yet recent model runs highlight competing influences of mild southerly advection versus occasional northerly intrusions that can briefly drop readings below 15 °C. Traders therefore see balanced probabilities between cooler and warmer outcomes as the four-day forecast horizon still allows significant adjustments from updated 00Z and 12Z runs.