Recent Met Office and ensemble model guidance for London on August 20 points to a daytime maximum near 22–23°C under variable cloud cover and a risk of scattered showers, which explains the tight clustering of market-implied odds between those two outcomes. Atlantic frontal influences and moderating high pressure have replaced earlier heatwave conditions, keeping afternoon temperatures from climbing higher while limiting radiative cooling that might push the peak lower. Minor differences in timing of any showers or breaks in cloud across model runs create the narrow edge for 22°C, with traders weighting official short-range updates most heavily ahead of the final 24-hour forecast window. Historical August averages near 21–22°C provide context, but current steering patterns favor the observed consensus.