**Persistent heat dome conditions are driving unusually warm overnight lows in Chicago for September 1, 2026.** Multiple forecasts indicate a minimum temperature in the mid-to-upper 70s, with official and ensemble guidance showing lows near 76–80 °F under southerly flow, high dew points in the 70s, and limited nocturnal radiative cooling. This setup stems from a broad upper-level ridge and associated warm-air advection from the south-central U.S., which has maintained elevated temperatures and humidity through late August into early September—well above the 1991–2020 normal low of ~62 °F. Trader consensus clusters tightly around the 70–81 °F bins (each 24.5–26 %) because model spread is modest, centered on the influence of any overnight cloud cover, weak showers, or minor wind shifts that could nudge the exact minimum by a degree or two. Lower-probability cooler outcomes (e.g., 68–69 °F or below) would require faster clearing and drier air than currently projected, while extremes above 82 °F remain possible only if mixing or advection stays stronger than expected. The market thus reflects the narrow uncertainty band in short-range guidance for this specific heat-event minimum.