National Weather Service guidance and short-range ensemble models currently project a daytime high near 79°F for Chicago on May 18, driven by southerly flow ahead of a warm front that will advect warmer air from the Gulf region. This setup places readings several degrees above the May 18 climatological normal of 71°F and supports the market’s leading 74.5% implied probability for a high of 78°F or above. Consistent model agreement and a modest severe-weather risk noted by the Storm Prediction Center further anchor trader sentiment. Any meaningful downward revision would require an unexpected cold-air intrusion or major shift in steering patterns, though the short forecast horizon and stable synoptic setup make such changes unlikely before resolution. Updated NWS guidance over the next 24 hours will refine the exact maximum.