Current forecasts from the National Weather Service and other models indicate a Monday low near 55–59°F for Chicago on September 28, consistent with late-September climatology moderated by Lake Michigan’s thermal inertia. Trader sentiment remains closely split between sub-45°F and 64°F-plus outcomes because ensemble guidance shows notable spread in boundary-layer advection and overnight radiative cooling potential. Northerly flow strength, cloud cover, and the precise position of a weak surface high will determine whether clear, calm conditions allow temperatures to drop sharply or whether residual warm air and lake-modified winds hold minima higher. Updated model runs and short-term observations over the next 48 hours will likely narrow this uncertainty.