**Persistent extreme heat and limited overnight cooling are anchoring trader expectations for Dallas's August 21 low in the low-to-mid 80s.** Official guidance from the National Weather Service and AccuWeather points to an overnight low near 81–83°F under mostly clear skies, consistent with the tightly clustered market-implied probabilities for 82–83°F, 84–85°F, and 86–87°F. An Extreme Heat Warning remains in effect through the evening, reflecting a strong, warm air mass with daytime highs forecast near 106°F that restricts radiative cooling after sunset. Key scientific factors differentiating the leading outcomes include boundary-layer mixing from light winds, urban heat-island effects that retain warmth near the surface, and dew-point temperatures that limit how far the mercury can drop before reaching saturation. Minor variations in cloud cover or wind speed during the pre-dawn hours can shift the observed minimum by a degree or two at the official Dallas station, creating the narrow spread among the top three contracts. With no significant frontal passage or precipitation expected to alter the air mass, the market reflects consensus around typical late-summer nocturnal temperatures for the region rather than any sharp change in conditions.