Traders assign the highest probabilities to 26°C or 27°C because ensemble forecasts from the Met Office and European models show a narrow spread around those values for London on August 17, reflecting modest uncertainty in maximum temperatures under sunny intervals and light winds. Recent high-pressure dominance has produced stable conditions following earlier heat, but subtle differences in boundary-layer mixing and urban heat-island effects at official stations can shift the peak by 1–2°C. Lower odds on 28°C or above align with model consensus favoring mid-to-upper 20s rather than renewed warming, while probabilities below 25°C remain limited absent an unexpected frontal passage. Updated model runs and Met Office briefings over the next 24 hours will likely narrow the range before resolution.