Current forecast models indicate substantial uncertainty in London's minimum temperature for May 21, with closely matched 41% implied probabilities for 7°C or below versus 17°C or higher driven by variable springtime atmospheric dynamics. The position of the jet stream and potential influence from Atlantic low-pressure systems could advect cooler maritime air, favoring lower readings, while a strengthening high-pressure ridge might suppress cloud cover and allow milder overnight temperatures. Official guidance from the UK Met Office and ensemble runs from the European Centre for Medium-Range Weather Forecasts show diverging solutions over the next several days, consistent with historical May variability where nighttime lows typically range 8–14°C. Traders are monitoring updated model guidance and surface observations for resolution thresholds as the date nears.