**Forecast consensus from the National Weather Service and major models centers the overnight low for Chicago on August 23 around 58–62°F under mostly clear skies.** Clear conditions overnight will promote radiative cooling after a sunny day with highs near 74–76°F. Light north-to-northwest winds of 5–10 mph will limit mixing while dew points in the mid-50s cap how far temperatures can fall. Ensemble guidance and NWS point forecasts show tight clustering in the upper 50s to low 60s, matching the market’s leading bins of 60–61°F (35%) and 58–59°F (30%). Recent model runs have remained stable, with no significant shifts in the air mass or cloud cover expected. Historical late-August normals (lows near 66°F) underscore that the current pattern is slightly cooler than average but well within seasonal bounds. Traders are pricing the narrow uncertainty range between official guidance and minor local variations near the lakefront versus O’Hare.