The broad spread of probabilities across multiple temperature bins for Chicago’s high on May 19 reflects notable uncertainty in short-range forecast guidance. Numerical weather prediction models show a consensus favoring highs in the mid- to upper 70s, yet ensemble spreads indicate potential for either modest warming from southerly flow or cooling tied to increased cloud cover and a passing frontal boundary. National Weather Service and private-model runs continue to diverge on boundary-layer moisture and daytime mixing, keeping lower-80s outcomes in play while limiting the likelihood of extremes below 70 °F or above 84 °F. Updated model cycles over the next 24–48 hours will narrow the range ahead of the market’s resolution.