Comparing Estimated HDD Via ECM/CFS and AI Models for Week 4-6 Ahead

Climate Impact Company Early U.S. Notes

Issued: Thursday November 13, 2025

Highlight: New operational HDD forecasts, West and Mid-south storms ahead, evolving 11-15-day snow cover.

Fig. 1-2: The U.S. gas population weight HDD forecast utilizing all models, their consensus, and comparison with 24 hours ago and the 10-year/30-year normal (left) plus the estimated CFS V2/ECM Vs. AI HDD projections for week 4-6.

Discussion: The U.S. gas population weight HDD forecast shifts warmer than normal next week and Thanksgiving week (Fig. 1). In fact, next week is adjusted slightly warmer while low demand for heating Nov. 21-27 is revised lower. The CFS V2 forecast for weeks 4-6 ahead is too volatile for operational use. Therefore, beginning today, Climate Impact Company estimates HDD for week 4-6 ahead comparing a consensus between ECM and CFS V2 operational forecasts and AI models (Fig. 2). Today’s week 4-6 outlook by ECM/CFS V2 consensus is slightly warmer than the 10-year normal while all AI models are considerably colder. The ECM/CFS V2 most closely matches the Climate Impact Company constructed analog (CIC-CA) forecast which favors cold North-central and warmth to the south.

November has tendency to bring big storms. Today’s NBM precipitation amount forecast into early next week unloads heavy rain (and mountain snow) on the West U.S. centered on California as an “atmospheric river” storm track arrives (Fig. 3). High wind accompanies the storminess. In the 6-10-day period the upper trough producing the heavy precipitation shifts to the Mid-south States where heavy rain and severe storms are likely. NBM indicates ?5 inches of rain is possible in southwest Arkansas (Fig. 4).

In the 11-15-day period, anticipated is significant snowfall across the North-central U.S. and Upper Midwest (Fig. 5). The snow cover allows an upper trough to emerge (Fig. 6) which could linger well into December.

Fig. 3-4: NBM 1-5-day precipitation amount forecast for the West U.S. and 6-10-day precipitation amount forecast for the East U.S.

Fig. 5-6: ECM 11-15-day snowfall forecast across the North-central U.S. and ECM 16-20-day upper air projection for North America.