GFS vs ECMWF Demand-Hub Outlook: 00Z Aug 14, 2026

Executive Summary

The 15-day outlook shows a significant bullish divergence, with the GFS forecasting much stronger cooling demand than the ECMWF. This GFS-hotter solution projects an additional 36 demand-weighted Cooling Degree Days (CDDs) nationally. The disagreement is most pronounced in the Midwest and South during the 8-15 day period, reducing overall forecast confidence despite a reasonable near-term agreement.

Hub-Level Weather

The primary driver of the national forecast divergence is the Midwest (Chicago), which accounts for 35% of the demand weighting. - Midwest (Chicago): The models show a massive split. The GFS forecasts 155.2 cumulative CDDs, while the ECMWF projects only 89.7 CDDs and introduces 6.3 Heating Degree Days (HDDs) late in the period. This difference stems from a significant cool down in the ECMWF forecast from August 21st onward, which the GFS does not see. - South (Atlanta): A similar, large disagreement exists here, with the GFS accumulating 324.8 CDDs versus the ECMWF's 252.5 CDDs. The GFS is notably hotter during the August 17-20 period. - East (New York City): The GFS is also warmer here with 188.9 CDDs against the ECMWF's 173.2 CDDs, though the disagreement is less extreme than in the Midwest. - South Central (Houston): Both models show strong, consistent heat. The GFS is slightly hotter, projecting 343.0 CDDs compared to the ECMWF's 327.0 CDDs.

Demand Implications (Natural Gas)

The competing forecasts present very different scenarios for late-August Natural Gas consumption. - The GFS outlook (204.3 weighted CDDs) implies a continuation of strong summer power burn for air conditioning, a supportive signal for NG prices. - The ECMWF's cooler forecast (168.3 weighted CDDs), driven by a late-month cooldown in the Midwest, suggests a more rapid seasonal decline in demand. This scenario would be bearish relative to the GFS and market expectations based on the hotter model. - The latest model runs have drifted slightly further apart, with the GFS adding 0.28 weighted CDDs and the ECMWF subtracting 0.73 weighted CDDs versus the prior cycle.

Model Agreement & Caveats

Confidence in the 15-day forecast is moderate to low due to significant model disagreement in the extended range. - Convergence: The overall convergence score is 0.84, which reflects good agreement over the next 5-7 days but masks the major divergence that emerges in the second half of the forecast. - Caveats: The primary uncertainty is the evolution of the pattern in the 8-15 day period, specifically whether the ECMWF's cooler solution for the Midwest and GFS's hotter solution for the South proves correct. Given the large demand weight of these regions, resolution of this model disagreement will be critical for price discovery. - Source: This analysis is based on GFS and ECMWF model data aggregated by Open-Meteo. The use of a few discrete city locations to represent broad demand regions is an approximation.