Latest U.S. CDD Forecast Maintain Late Calendar Summer Heat

Climate Impact Company U.S. Medium Range Report

Issued: Thursday September 3, 2026

Highlight: Mid-south heat continues. Gradually warmer West. Mid-Atlantic is warm. Northeast is cool extended range.

Charts of the day: Latest U.S. CDD forecast; Weekly Summer 2026 CDD.

Discussion: The late calendar summer U.S. population weight CDD forecast emphasizes excessive cooling demand. Weekly summer 2026 U.S. population weight CDD indicate the majority of weeks were warmer than the 10-year climatology.

Medium-range 6-10 Day Forecast Valid September 8-12, 2026 (ECM ENS and 24-hour change)

Discussion: The Southwest shifts warmer as wet monsoon moisture is less than previously indicated. The Mid-south torrid heatwave continues. Heat extends to the Southeast States and Carolinas. ECM ENS is the number 1 skill score for the 6-10-day period.

Medium-range 11-15 Day Forecast Valid September 13-17, 2026 (AI Weather Next V2 and 24-hour change)

Discussion: AI Weather Next V2 is the number 1 skill score for the 11-15-day period. Anomalous heat is maintained although with less amplitude. Warmth broadens across the East.

U.S. Medium-range Precipitation Forecast

Discussion: ECM ENS indicates wet weather near the U.S./Canada border in the 6-10-day period plus Old Mexico. In the 11-15-day period, lack of significant precipitation anomalies is indicated.

Days 16-20 Extended range Temperature Forecast valid September 18-22, 2026

Discussion: Broadening warmth, especially for the West, while the Northeast is cool is implied by lead-in GFS/ECM ENS upper air forecasts to begin the period. A potential tropical cyclone is indicated in the Gulf of America.