GFS vs ECMWF Demand-Hub Outlook: 2026-04-11 00Z

Executive Summary

Both GFS and ECMWF models forecast a transition from modest heating demand to early-season cooling demand over the next 15 days, consistent with the spring shoulder season. The models have converged significantly on a warmer outlook versus the prior cycle, especially the ECMWF. The primary disagreement, and main source of forecast uncertainty, lies in the timing and intensity of cooler air masses moving into the Midwest and South Central hubs during the Day 8-15 period.

Hub-Level Weather

The national forecast is primarily driven by the Midwest (Chicago, 35% weight) and the East (New York City, 30% weight).

• Midwest (Chicago): This hub is the largest source of model disagreement (mean_abs_hdd_diff_by_day: 7.30). While cumulative HDDs are similar (GFS: 112.5, ECMWF: 107.0), the timing differs materially. The GFS forecasts sharp, intermittent cool-downs around April 18 and April 24-25, whereas the ECMWF suggests a more consolidated and intense cold shot from April 19-23.
• East (New York City): Agreement is stronger here. The ECMWF is notably warmer mid-period, generating more cooling demand (32.2 cumulative CDDs) compared to the GFS (23.3 cumulative CDDs), particularly around April 17.
• South Central (Houston): The models show a significant divergence in cooling demand. The GFS is consistently hotter, forecasting 156.3 cumulative CDDs versus only 117.2 for the ECMWF. This is driven by a cooler period in the ECMWF around April 19-21 that the GFS does not see.

Demand Implications (Natural Gas)

The overall outlook points to generally light, below-normal weather-driven gas demand for this time of year.

• Heating Demand: Lingering heating demand will be concentrated in the Midwest and Northeast. The total weighted 15-day heating load is very similar between models (GFS: 84.9 HDD, ECMWF: 82.3 HDD). However, the day-to-day volatility in the Midwest forecast by both models could create swings in regional spot gas prices.
• Cooling Demand: Early-season cooling load is emerging, primarily in the South. The GFS's hotter solution in Texas and the Southeast (total weighted CDDs of 45.1 vs. ECMWF's 40.8) implies a stronger call on natural gas for power generation. The nearly 40 CDD difference in Houston is the most significant demand delta between the two models.

Model Agreement & Caveats

Confidence in the 15-day outlook is moderate to high, having improved from the previous cycle.

• Convergence: The national convergence_score is 0.20, indicating reasonable agreement. This is a marked improvement from the prior cycle, with the score decreasing by 0.047.
• Run-over-Run Shift: Both models trended significantly warmer compared to their previous runs. The ECMWF made a particularly large bullish shift, shedding 22.1 weighted HDDs, while the GFS dropped 8.5 weighted HDDs. This convergence toward a warmer solution increases confidence in the near-term mild pattern.
• Caveats: The primary caveat is the low confidence in the Day 8-15 period, where the character and timing of cool shots in the central U.S. remain uncertain. This analysis uses Open-Meteo's model interpretation and simplified demand weights, which may differ from other proprietary systems.