Latest Met Office and ECMWF ensemble guidance point to a London maximum near 15 °C on May 18, driven by persistent northerly flow that continues to advect cooler maritime air across southern England. This pattern has held daytime readings 2–3 °C below the mid-May climatological average of 17–18 °C, with extensive cloud cover limiting surface heating and only modest diurnal warming expected under light winds. Model consensus remains tight around the 14–16 °C band, reflecting stable steering patterns and minimal upper-level ridging that would otherwise allow warmer southerly advection. Traders are therefore pricing the narrow range heavily while assigning low probability to outliers, as any late-day clearing or slight wind shift could nudge readings one degree higher without altering the overall cool regime.