GFS vs ECMWF Demand-Hub Outlook: 2026-04-10 00Z

Executive Summary

The 15-day outlook indicates a notable divergence between the GFS and ECMWF models, primarily centered on heating demand in the Eastern U.S. The ECMWF forecasts a significantly colder pattern, implying stronger late-season natural gas demand for heating compared to the GFS. Both models are in strong agreement on building cooling demand across the South, consistent with the seasonal transition.

Hub-Level Weather

The key drivers of the national forecast are the major population centers in the Midwest and East, which show the most significant model disagreement.

• East (New York City, 30% weight): This hub shows the most impactful divergence. The ECMWF is materially colder, forecasting 116.1 cumulative HDDs versus the GFS's 96.4 HDDs. The disagreement is most pronounced in the latter half of the forecast period, particularly on April 24th, where the ECMWF sees 16.8 HDDs to the GFS's 2.4 HDDs.
• Northeast (Boston, 10% weight): The models show their largest absolute disagreement here, with the ECMWF forecasting 189.1 HDDs against 151.4 HDDs from the GFS. This reinforces the colder solution for the broader Northeast region in the ECMWF.
• Midwest (Chicago, 35% weight): While the largest weighted hub, model agreement is better here than in the East. Cumulative HDDs are closely aligned (GFS 138.5, ECMWF 142.9), though there is significant daily variability in the back half of the forecast.
• South (Houston & Atlanta): Both models are in tight agreement on a pattern of building warmth and cooling demand. Houston shows cumulative CDDs of 165.4 (GFS) and 159.7 (ECMWF) with zero heating demand expected.

Demand Implications (Natural Gas)

The forecast reflects a classic shoulder season dynamic, with weather-driven demand transitioning from heating to cooling.

• Heating Demand: The national weighted forecast shows the ECMWF calling for more heating load (104.4 weighted HDDs) than the GFS (93.4 weighted HDDs). The ECMWF scenario would extend residential/commercial heating demand longer into April, particularly in the high-consumption Northeast markets. The GFS solution suggests a quicker drop-off in heating needs.
• Cooling Demand: Both models signal robust and building demand for power generation to meet air conditioning load in the South. The national weighted cumulative CDDs are nearly identical between the models at 45.2 (GFS) and 46.7 (ECMWF).

Model Agreement & Caveats

Confidence in the forecast is moderate to low, especially for the 8-15 day period in the eastern half of the country.

• Convergence: The weighted_mean_abs_hdd_diff_by_day is 3.05, indicating a non-trivial level of daily disagreement between the models on a national scale.
• Run-over-Run Trends: The models show instability compared to their prior runs. The GFS trended colder (added +1.07 weighted HDDs), while the ECMWF trended warmer (removed -1.77 weighted HDDs). This opposing trend reduces overall forecast conviction. Both models trimmed expected cooling demand from the prior cycle.
• Source Notes: This analysis is based on GFS and ECMWF model data from Open-Meteo using a 65°F degree day base. Forecast accuracy typically decreases beyond 7-10 days.