Latest Met Office and ensemble model guidance point to a highest temperature in London on May 18 clustering tightly around 15–16 °C, as a moderate Atlantic low-pressure system delivers variable cloud cover, light southwesterly winds, and scattered showers that limit surface heating. Mid-May climatology normally favors 16–17 °C maxima, yet cooler-than-average spring conditions this year have kept radiative cooling stronger overnight and daytime insolation reduced, splitting probability among the 14 °C, 15 °C, and 16 °C contracts. Updated runs show only modest spread tied to exact cloud timing and shower placement, with any unexpected clearing potentially pushing readings toward 17 °C while lingering rain would cap them near 14 °C. Traders are therefore pricing genuine forecast uncertainty rather than a single dominant scenario ahead of the final 48-hour model updates.