GFS vs ECMWF Demand-Hub Outlook: 2026-04-09T00:00Z

Executive Summary

The 15-day outlook shows a classic shoulder season pattern, with lingering heating demand in the northern U.S. giving way to emerging cooling demand in the South. The GFS and ECMWF models are in general agreement on the national trend but diverge on regional specifics; GFS forecasts a colder Midwest and a significantly hotter South, while ECMWF is colder in the East. Both models trended substantially warmer in this cycle, reducing the total heating demand forecast, particularly in the GFS (-43.3 weighted HDDs).

Hub-Level Weather

The national picture is primarily driven by the Midwest and East, which account for 65% of the demand weighting.

• Midwest (Chicago, 35% weight): This is the main point of contention for heating demand. The GFS is materially colder, forecasting 158.9 cumulative HDDs versus the ECMWF's 129.1 HDDs. The largest disagreements occur in the day 6-10 period (e.g., April 15-16) and again near the end of the forecast, where GFS sees sharper cold intrusions.
• East (New York City, 30% weight): The models show the opposite disagreement here, with the ECMWF being colder at 129.4 cumulative HDDs compared to the GFS's 108.2 HDDs. The key divergence is in the latter half of the forecast (e.g., April 19), where ECMWF maintains stronger heating demand.
• South Central & South (Houston/Atlanta, 25% total weight): Both hubs show a strong signal for emerging cooling demand, but the GFS is significantly more aggressive. For Houston, GFS forecasts 177.8 cumulative CDDs versus 137.0 CDDs from the ECMWF. The pattern is similar in Atlanta (GFS: 154.7 CDDs, ECMWF: 101.2 CDDs).

Demand Implications (Natural Gas)

The forecast implies a net reduction in weather-driven natural gas demand as significant heating load abates.

• Heating Demand: The outlook is for below-normal heating demand, especially given the significant warmer trend versus the prior model cycle (delta_weighted_cumulative_hdd_gfs: -43.3). The GFS's colder Midwest scenario would support regional cash prices more than the ECMWF's milder solution.
• Cooling Demand (Power Burn): The GFS projects a much stronger start to the cooling season, with its forecast for the South (Houston, Atlanta) implying a notable increase in gas-for-power generation. The ECMWF presents a more moderate and delayed start to significant cooling load.
• Net Impact: The GFS solution is higher-risk, with potential for both late-season heating and early-season cooling. The ECMWF suggests a more benign, lower-demand transition period.

Model Agreement & Caveats

Confidence in the 15-day outlook is moderate due to key regional disagreements in the medium-to-long range.

• Convergence: The convergence_score of 0.218 and a weighted_mean_abs_hdd_diff_by_day of 3.58 indicate a non-trivial level of disagreement between the models. Confidence is highest in the first 5-7 days and decreases thereafter.
• Run-over-Run Shift: The forecast saw a significant shift warmer (delta_weighted_cumulative_hdd_gfs: -43.3, delta_weighted_cumulative_hdd_ecmwf: -19.9). This large adjustment reduces confidence and highlights the volatility in the medium-range pattern.
• Source Limitations: This analysis is based on GFS and ECMWF model data from Open-Meteo using a predefined set of demand hubs and weights. It does not incorporate other operational models (e.g., Canadian) or proprietary weighting schemes.