**Incoming cold air is driving Beijing's expected high on September 30 toward the low 20s °C.** A stronger-than-average northwest flow and clear, dry conditions are forecast to limit daytime heating after a mild September 29, with official guidance and model consensus pointing to a maximum near 20–22 °C. This places 21 °C and 22 °C as the clear market leaders at 47.5 % and 33.0 % implied probability. The shift follows several days of gradual cooling and aligns with climatological patterns for late-September cold-air intrusions, which often produce daily highs 2–4 °C below the 23.2 °C long-term average. Limited model spread and dry air support low odds for outcomes above 23 °C or below 20 °C. Updated National Meteorological Center guidance and any last-model runs before resolution will be the key near-term catalysts.