Recent Met Office and ECMWF ensemble forecasts converged on a daytime maximum of 18°C in London on May 17 under partly cloudy skies and moderate westerly flow, anchoring the market's overwhelming consensus at 99.7% for that outcome. This positioning reflects the high reliability of short-range numerical weather prediction models when synoptic patterns remain stable, with limited potential for rapid warming from Atlantic air masses or radiative heating. Official resolution will hinge on verified measurements from stations such as Heathrow or Kew Gardens, where deviations from the forecast maximum typically stay within 1–2°C under these conditions. A sudden clearing of cloud cover or stronger southerly advection could push readings to 19°C or above, though current guidance shows low probability for such shifts before the daily peak.