Forecast uncertainty in overnight radiative cooling drives the near-even split between sub-52°F and 70°F+ lows for Denver on September 16. Official guidance shows afternoon highs in the low-to-mid 80s under scattered thunderstorms and variable cloud cover, with overnight lows projected near 56–59°F depending on the timing of clearing skies and wind. Denver’s mile-high elevation amplifies diurnal swings, as clear, calm nights enable rapid heat loss while lingering clouds or moisture from convection trap warmth. Current model consensus favors mid-50s readings consistent with seasonal norms around 49°F, yet small shifts in frontal timing or thunderstorm outflow could push the minimum either below 52°F or well above 60°F. Updated National Weather Service and NOAA model runs over the next 48 hours will likely resolve the key variables.