Recent National Weather Service forecasts for Chicago on August 31 point to a high in the upper 80s under partly sunny skies with southwest winds, supporting the market's narrow lead for the 88-89°F bin. Southerly flow is advecting warmer, more humid air ahead of a modest trough, while afternoon mixing and limited cloud cover will determine whether readings peak near 88°F or edge into the low 90s. Model consensus shows tight clustering around these values with minor spread from timing of any weak disturbances, keeping 90-91°F probabilities close behind. Historical August climatology for the city features typical highs near 80°F, so the current pattern represents a modest positive anomaly that traders are pricing with real uncertainty tied to the next model runs and surface observations.