Forecast uncertainty in short-term numerical weather prediction models is the main driver behind the near-even split between 4°C-or-below and 14°C-or-higher outcomes for Moscow’s minimum on September 27. Recent GFS and ECMWF runs show divergence in the steering of a mid-tropospheric trough and associated cold-air advection from northern latitudes versus milder Atlantic flow; small shifts in the 500-hPa height field or surface high placement can swing the overnight low by 8–10 °C. Climatological norms for late September place the typical minimum near 8–10 °C, so the market-implied probabilities capture both the risk of an early Arctic outbreak and the more common transitional regime. Updated model cycles and observational data from the next 48 hours will likely resolve much of the spread.