Ensemble forecasts from the Met Office and ECMWF currently center London’s maximum temperature for May 18 near 14–16 °C, driving the market’s highest implied probability toward 15 °C amid an unsettled Atlantic low-pressure system tracking across the UK. This synoptic pattern favors modest daytime warming under variable cloud cover and scattered showers, keeping afternoon peaks below the seasonal climatological mean of roughly 16–17 °C for mid-May. Recent model runs show tight clustering in that 14–16 °C envelope with limited upside potential from clearer skies or stronger southerly flow, while historical analogs indicate that similar May setups rarely exceed 17 °C in the London area. Traders are therefore assigning the bulk of probability to the narrow 14–16 °C range as the day’s official high is monitored.