Forecast models from sources including the Met Office, NOAA-influenced ensembles, and regional Polish meteorological services indicate Warsaw's overnight low on September 21 will likely settle near 10–11 °C, driven by persistent cloud cover that suppresses radiative cooling, moderate westerly winds advecting mild maritime air, and scattered showers maintaining dew points near 9–10 °C. These conditions limit the typical autumnal temperature drop seen under clear skies, while slight variations in model timing of the minimum—whether just before dawn or during early evening showers—create the tight 50 % split between the two leading outcomes. Historical September minima in Warsaw average around 11 °C, providing context for why traders assign only modest probability to sub-9 °C readings despite the unsettled pattern. Updated high-resolution runs and surface observations through the evening will refine the exact threshold before resolution.