Recent Met Office guidance points to a daytime maximum of 23 °C in London on 20 August amid a changeable Atlantic flow, with ensemble spreads from global models clustering tightly between 22–24 °C. Primary differentiating factors include the precise timing and strength of any embedded fronts, boundary-layer cloud cover that modulates daytime heating, and low-level wind direction that controls advection of cooler maritime versus warmer continental air. Two-day forecast uncertainty remains elevated because small shifts in jet-stream position or convective initiation can alter peak temperatures by 1–2 °C. Traders therefore assign nearly equal implied probabilities to the three leading outcomes, reflecting the narrow but genuine spread in the latest model runs rather than a settled consensus.