A strong heatwave driven by high pressure and southerly warm-air advection has elevated forecast overnight minima for London on June 23, 2026, to the 20–24 °C range according to the latest Met Office and ECMWF guidance. This positions the 20 °C outcome as the market leader because ensemble means cluster near that value, while residual model spread—particularly in boundary-layer humidity and cloud cover—keeps modest probabilities on both 24 °C or higher and slightly cooler 17–19 °C bins. Historical mid-June minima average 12–13 °C, so the current anomaly reflects the atypical persistence of the warm airmass rather than typical radiative cooling under clearer skies. Updated model runs and official briefings over the next 48 hours will determine whether the minimum settles closer to 20 °C or edges toward the higher thresholds.