GFS vs ECMWF Demand-Hub Outlook: 2026-07-19T00:00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the GFS forecasting substantially stronger national cooling demand than the ECMWF. The GFS projects 209.1 weighted CDDs versus the ECMWF's 179.4, a difference of nearly 30 CDDs. This divergence is amplified by the latest model runs, as the GFS trended significantly hotter (+34.3 CDDs) while the ECMWF trended sharply cooler (-44.1 CDDs), signaling low forecast confidence.

Hub-Level Weather

The primary drivers of the national forecast difference are the East and South, where the GFS is materially hotter, particularly in the 8-15 day period.

• East (New York City): This is the largest point of disagreement. The GFS forecasts 203.8 cumulative CDDs, a massive 49.8 CDDs more than the ECMWF's 154.0. The divergence grows substantially after July 28th, with the GFS maintaining heat while the ECMWF shows a significant cooldown.
• Midwest (Chicago): In contrast to the national picture, the ECMWF is warmer here, projecting 168.2 CDDs versus the GFS's 152.9. The ECMWF shows a stronger heat event from July 24-27 before both models cool.
• South Central (Houston) & South (Atlanta): Both hubs show a much hotter GFS solution. Houston is +57.6 CDDs on the GFS, and Atlanta is a remarkable +101.9 CDDs hotter, with most of this difference occurring after July 29th.

The Midwest (35% weight) and East (30% weight) are the largest demand hubs in this analysis. The GFS's extreme heat signal in the East is the primary factor driving its national total higher than the ECMWF.

Demand Implications (Natural Gas)

The current outlook points to robust cooling demand for natural gas (power burn) over the next two weeks, though the intensity is highly uncertain.

• GFS Scenario: The 209.1 weighted CDDs signal a prolonged period of strong, above-normal cooling demand, particularly across the eastern half of the country. The significant addition of +34.3 CDDs in this run is a bullish market signal.
• ECMWF Scenario: At 179.4 weighted CDDs, this model also forecasts above-normal demand but suggests a less intense and shorter-lived heat event, with notable cooling in the East and South in the 8-15 day range. The removal of -44.1 CDDs from its prior forecast is a distinctly bearish pressure.

Model Agreement & Caveats

Forecast confidence is low. While the provided convergence score is high at 0.9986, this appears to be driven by agreement on zero HDDs and is not representative of the material disagreement on CDDs.

The primary reasons for low confidence are: 1. Large CDD Divergence: A ~30 weighted CDD gap between the models over 15 days is significant. 2. Opposing Run-Over-Run Trends: The GFS adding significant heat (+34.3 CDDs) while the ECMWF sheds it (-44.1 CDDs) points to high instability and uncertainty in the long-range pattern.

This analysis is based on raw, unprocessed model data from Open-Meteo and does not represent a final, value-added forecast.