Recent National Weather Service guidance points to overnight lows near 58–66°F for Chicago on August 25, with the precise minimum hinging on evolving cloud cover, wind speeds, and boundary-layer moisture ahead of a modest warm-up. Clear or partly cloudy skies under high pressure would enhance radiative cooling after sunset, favoring readings in the upper 50s, while increased clouds or a light southerly flow could limit drops to the mid-60s. Lake Michigan’s moderating influence and typical late-August humidity levels add further variability, as even modest changes in dew points or mixing can shift the minimum by several degrees. With leading market outcomes clustered around 58–59°F yet substantial probability assigned to both cooler and warmer bins, traders are pricing in the inherent spread among short-range model solutions before final NWS observations at O’Hare resolve the market.