National Weather Service forecasts and ensemble model guidance indicate a daytime high well above 64°F for Chicago on May 17, driven by southerly flow ahead of an approaching warm front that favors readings near the climatological normal of 70.9°F at O’Hare International Airport. This atmospheric setup, supported by stable steering patterns over the Midwest, underpins the market’s near-certain consensus for the 64°F-or-higher outcome while reflecting historical May temperature distributions. Only an unforecast sharp cold-air intrusion or major model error could realistically produce a lower maximum, though such shifts remain low-probability given the short forecast horizon and consistent guidance.