GFS vs ECMWF Demand-Hub Outlook: 2026-06-20 00z

Executive Summary

The 15-day outlook points to strong national cooling demand, with the GFS (151.1 wCDD) and ECMWF (148.1 wCDD) in close agreement on the total demand-weighted load. However, significant regional differences exist, with the GFS forecasting a much hotter pattern in the South and a cooler pattern in the Midwest. The models diverged from the prior cycle, with the GFS trending cooler and the ECMWF warmer, reducing overall forecast confidence.

Hub-Level Weather

The national forecast is primarily driven by cooling demand in major population centers, but key model disagreements introduce regional uncertainty.

• Midwest (Chicago, 35% weight): This is a primary point of disagreement. The GFS is materially colder, forecasting 12.0 HDDs versus only 2.3 HDDs from the ECMWF. This suggests the GFS sees intermittent cool shots impacting heating and cooling demand, while the ECMWF is milder and more stable.
• South Central (Houston, 15% weight): The GFS is significantly hotter, projecting 312.6 cumulative CDDs compared to the ECMWF's 271.1 CDDs. This +41.5 CDD difference over the 15-day period is a major driver of the GFS's higher national demand profile.
• South (Atlanta, 10% weight): The GFS is also much hotter in the Southeast, forecasting 248.8 CDDs against the ECMWF's 187.0 CDDs.
• East (New York City, 30% weight): Models are in better alignment here, though the ECMWF is slightly warmer, forecasting 168.0 CDDs to the GFS's 158.0 CDDs.

Demand Implications (Natural Gas)

The overall forecast is supportive of strong natural gas demand from the power sector for air conditioning load.

• Both models project a robust cooling demand total (~148-151 wCDD) over the next 15 days, which implies above-normal power burn for this period.
• If the GFS solution proves more accurate, gas demand in ERCOT (Texas) and the Southeast will be stronger than the ECMWF suggests.
• Conversely, the GFS's cooler outlook for the Midwest would temper some residential/commercial and power demand in that key region, particularly in the first week of the forecast. The ECMWF's outlook implies more consistent cooling demand across the northern U.S.

Model Agreement & Caveats

• Confidence: The national convergence score is 0.778, indicating moderate agreement on the total demand picture. However, confidence is lowered by a notable decrease in agreement (-0.063) since the prior model run.
• Run-over-Run Shift: The models moved in opposite directions. The GFS trended cooler overall (-6.1 wCDD), while the ECMWF trended warmer (+2.5 wCDD). This opposing trend is a sign of instability and warrants caution when trading on the long-range outlook.
• Source Notes: This analysis is based on Open-Meteo's processing of GFS and ECMWF model data for specific hub locations. The demand weights are simplified proxies for regional gas consumption.