Recent ensemble forecasts from models including GFS and ECMWF place the September 19 overnight minimum in Helsinki near 11–13 °C, supporting the 46 % market-implied probability on 12 °C. Persistent southwesterly flow, extensive cloud cover, and scattered showers are limiting nocturnal radiative cooling over the Baltic region, keeping surface temperatures several degrees above the long-term September average low of roughly 9 °C. Recent observations show the city has run 1–2 °C warmer than climatology through mid-month, with no incoming Arctic air mass expected before resolution. Model spread remains modest at this 48-hour lead time, though small shifts in cloud timing or wind speed could still move the realized minimum into the 10–11 °C range favored by roughly 40 % of trader volume. Updated high-resolution runs and the Finnish Meteorological Institute’s final guidance ahead of the date will provide the last key inputs.