Increased cloud cover and rounds of showers and thunderstorms are the primary factors capping Chicago's August 13 high temperature outlook in the mid- to upper 70s, well below the seasonal normal near 83°F. National Weather Service guidance and model consensus emphasize reduced solar heating from persistent moisture and convective activity, with forecasts clustering around 76–79°F as the most probable range. This setup reflects a broader pattern of unsettled conditions across the Midwest that has limited daytime warming compared with clearer, hotter analogs. Traders assign the highest implied probabilities to the 76–77°F and 78–79°F bins, reflecting tight consensus while acknowledging remaining uncertainty in exact convective timing and coverage. Fresh NWS updates and morning model runs on August 13 will provide the final data for market resolution.