**Persistent summer heat and high humidity are anchoring overnight lows near 78–81°F in Houston for August 21.** Official National Weather Service and private forecasts as of August 20 project a Friday night low in the upper 70s to low 80s under mostly clear to partly cloudy skies, light southwesterly winds, and dew points remaining in the mid-70s. These conditions limit radiational cooling after daytime highs near 98–101°F. Recent overnight minima have consistently fallen in the 78–82°F range amid an ongoing heat pattern with no approaching cold front or significant rain to enhance cooling. Market-implied odds cluster tightly around 78–81°F because ensemble guidance shows only modest variability in minimum temperature, driven mainly by small differences in cloud cover and boundary-layer mixing. Lower bins (72–77°F) carry meaningful but secondary probability reflecting the chance of clearer skies or slightly drier air allowing more cooling, while higher outcomes remain discounted absent any major warm-air advection or stalled fronts. Historical August 21 lows average ~76°F, but current synoptic conditions support the market’s elevated range. Updated model runs and NWS evening forecasts will be the next key data points traders monitor.