Incoming northerly flow and associated frontal boundary are driving the primary shift for Istanbul's September 22 low temperature, with models showing increased cloud cover, scattered rain or thunderstorms, and daytime highs dropping to around 21°C from the prior 25–26°C readings. Official guidance and ensemble forecasts place the overnight minimum near 14–16°C under partly to mostly cloudy skies and moderate northerly winds, though exact values hinge on precipitation timing, cloud thickness, and boundary-layer mixing. This setup creates genuine uncertainty between a cooler scenario near or below 15°C versus a milder outcome above 18°C if clearing occurs earlier, consistent with the closely matched market-implied odds near the 10°C-or-below and 20°C-or-higher thresholds. Updated short-range model runs from agencies like NOAA and ECMWF will refine the low over the next 48 hours ahead of resolution.