Traders have converged on the 74°F or higher outcome at near-certainty because National Weather Service model runs and surface observations confirm a robust high-pressure ridge advecting warm southerly flow across the Midwest, pushing Chicago’s maximum temperature well above the long-term May 15 normal of 70°F at Midway Airport. Synoptic conditions, including minimal cloud cover and light winds, have sustained afternoon heating consistent with the 74°F threshold. The sole realistic scenario that could still shift resolution is an earlier or stronger lake-breeze front off Lake Michigan suppressing the peak reading into the low 70s, though current guidance shows that boundary arriving too late to prevent the daily high from exceeding 74°F.