Recent National Weather Service and ensemble model guidance indicate Chicago's overnight minimum on August 28 will likely fall in the low-to-mid 60s under mostly clear skies, light winds, and modest radiational cooling typical of late-summer high-pressure regimes. This consensus underpins the tight clustering of market-implied odds around the 62–65 °F bins. Differentiation among those bins hinges on small variations in dew-point depression, boundary-layer mixing, and urban heat-island effects near O’Hare versus downtown stations, plus any late-model adjustments to the 925 mb temperature field. Historical climatology places the date’s average low near 65 °F, so current probabilities embed a modest cool-side bias relative to long-term norms while still assigning meaningful tail risk to sub-60 °F outcomes if skies clear earlier than expected.