**Recent cooling from a multi-day storm system across Türkiye has shaped forecasts for Istanbul on August 31, 2026, with most models indicating overnight lows of 19–21°C under clearing skies.** A five-day period of thunderstorms and northerly winds, peaking around August 28–29, lowered temperatures by several degrees from prior heat and introduced cooler maritime air, but the system shifts east by the 30th, allowing high pressure and mostly sunny conditions to return. Scientific factors differentiating the closely bunched market outcomes (17°C or below at 29%, with 20–22°C bins near 25–26%) center on nocturnal radiative cooling, boundary-layer mixing, and local influences. Clear or mostly clear skies after the frontal passage promote efficient longwave radiation loss, while light-to-moderate northerly or northeasterly winds (often 5–15 km/h) can either enhance cooling via advection or limit it through turbulent mixing. Dew-point temperatures around 16–18°C and urban heat-island effects in Istanbul further modulate how far the mercury falls before dawn. Model consensus places the minimum near 19–21°C, consistent with late-August climatology after similar cool-air intrusions, yet two-day forecast uncertainty in exact wind speeds, residual moisture, or subtle cloud cover keeps probabilities spread across the 17–23°C range. Upcoming high-resolution model runs and official Turkish State Meteorological Service updates will likely tighten the distribution as the date approaches.