Recent National Weather Service guidance and ensemble model consensus indicate a daytime high near 80°F in Chicago on August 21, driven by southwest flow, partly cloudy skies, and surface temperatures climbing from morning lows in the mid-60s. This positions the 80-81°F bin as the market leader at 51.5% implied probability, with adjacent 78-79°F and 82-83°F ranges capturing residual model spread. Afternoon mixing and modest moisture return limit significant warming or cooling, while historical August climatology for the area centers near 77-82°F. Updated forecast discussions and any final model runs overnight will provide the last inputs before official observations determine resolution.