GFS vs ECMWF Demand-Hub Outlook: 2026-04-12T00:00Z

Executive Summary

The 15-day outlook shows a significant bullish divergence, with the GFS forecasting considerably more heating demand than the ECMWF. The national GFS forecast calls for 88.8 demand-weighted HDDs, compared to just 66.5 from the ECMWF. This difference is almost entirely driven by a late-period cold shot projected by the GFS into the high-demand Midwest hub, a solution the ECMWF does not currently see. Confidence in this colder GFS outlook is low, as the models have diverged further since the prior cycle.

Hub-Level Weather

• Midwest (Chicago, 35% weight): This hub is the primary source of model disagreement. The GFS forecasts 136.8 cumulative HDDs, nearly double the ECMWF's 76.0 HDDs. The divergence is concentrated in the latter half of the forecast, particularly from April 24-26, where the GFS projects a strong late-season cold event (e.g., 25.4 HDDs on April 24) that the ECMWF models as much milder (7.6 HDDs).

• East (New York City, 30% weight): The models are in close agreement on heating demand in this key region, with the GFS at 77.9 HDDs and the ECMWF at 78.9 HDDs. The GFS does project more early-period warmth, resulting in higher cooling demand (45.5 CDDs vs. 33.3 CDDs for the ECMWF).

• South Central (Houston, 15% weight): This region is dominated by cooling demand. The GFS is modestly hotter, projecting 136.6 CDDs versus the ECMWF's 121.1 CDDs.

Demand Implications (Natural Gas)

The GFS presents a significantly more constructive case for natural gas demand over the next two weeks. The additional ~22 weighted HDDs versus the ECMWF represent a material increase in late-season heating load, primarily for residential and commercial consumption in the Midwest.

However, the GFS has also trended notably less hot in its latest run, shedding 12.5 weighted CDDs cycle-over-cycle. This partially offsets the bullish HDD additions. The ECMWF, in contrast, trended slightly warmer, removing 1.8 weighted HDDs from its forecast. The net effect is a market signal muddled by significant model disagreement, particularly in the less certain 10-15 day period.

Model Agreement & Caveats

Confidence in the forecast is currently low.

• Convergence: The national convergence score is 0.27, indicating a moderate level of disagreement between the models. Crucially, this score increased by 0.07 since the last cycle, meaning the models are moving further apart, not toward consensus.
• Divergence: The weighted average absolute difference in HDDs per day is 2.69. This is driven by the Midwest hub (Chicago), which has a daily average difference of 4.81 HDDs.
• Caveats: The most significant forecast divergence occurs beyond Day 10, a period with inherently lower meteorological certainty. The GFS's colder solution should be viewed with caution until the ECMWF or other ensemble guidance begins to show a similar trend. This report is based on a single run from each model provided by Open-Meteo and may not capture the full ensemble range.