Divergent short-term forecast models for overnight radiative cooling create the tight 50-50 split between an 8°C-or-below minimum and 18°C-or-higher low on September 21. Southerly flow and increasing cloud cover from an approaching Atlantic front are expected to limit clear-sky heat loss, keeping Moscow’s minimum near 12–14°C in most guidance, yet small shifts in timing or thickness of low-level stratus could allow either stronger cooling or retained warmth. Historical September minima average near 8–10°C, but recent southerly advection has kept readings elevated. Fresh GFS and ECMWF runs plus Roshydromet updates in the next 24–48 hours will clarify whether the front arrives early enough to suppress the low or allows a brief clear window.