With market-implied odds clustered tightly around 14–16°C, traders are pricing the genuine uncertainty in short-range forecast guidance for London’s maximum temperature on May 18. Ensemble runs from the Met Office show a transitional pattern of Atlantic westerlies and variable cloud cover that limits daytime heating, while any break in the cloud deck could briefly push readings toward 16°C. Current sea-surface temperatures in the eastern North Atlantic and a relatively flat jet-stream configuration favor values near the seasonal May average of 15–17°C rather than sustained warmth. Resolution hinges on the precise timing and strength of any frontal passage, with the next model cycles expected to tighten the range before the market settles.