**Forecast consensus from the National Weather Service and local models points to a Denver high temperature on September 19, 2026, in the 77–79°F range, aligning closely with the market's leading outcomes of 76–77°F (41.5%) and 78–79°F (29.0%).** The NWS Denver/Boulder forecast explicitly calls for a 79°F high under scattered thunderstorms with a 70% chance of precipitation, while point forecasts and other sources (including Denver7 and Weather Atlas) show peaks near 77°F amid partly to mostly cloudy skies and afternoon convection. This matches the long-term September 19 average high of ~77.8°F. Key scientific drivers include Denver’s high elevation (~5,280 ft), which amplifies diurnal swings and allows rapid afternoon cooling from cloud cover and thunderstorms; a pattern of warm advection tempered by increasing moisture and instability typical for late September. Thunderstorm timing is critical—earlier or stronger convection could cap the high nearer 74–76°F, while delayed activity supports the upper 70s. Recent model runs and NWS updates through September 17–18 have remained stable with no major shifts, supporting trader focus on the narrow 76–79°F band. Historical analogs show similar late-summer setups frequently resolve in this range, though forecast uncertainty from convective timing keeps lower probabilities on 74–75°F (18.5%) and 80–81°F (8.0%). Updated NWS briefings and model runs ahead of the event remain the key near-term catalysts.