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Natural Gas Weather — Week of October 2, 2026

GFS vs ECMWF Demand-Hub Outlook: 2026-10-02 00:00 UTC

Executive Summary

The latest 15-day outlook reflects a pronounced divergence between weather models, with ECMWF projecting higher heating demand (46.51 demand-weighted HDDs vs. GFS at 38.22) driven by an aggressive late-period cold push into the Midwest. Conversely, GFS carries an unseasonably warm bias across the South and East, generating 60.01 demand-weighted CDDs compared to ECMWF’s 42.79. Run-over-run deltas show GFS trending warmer (+7.99 weighted CDDs, -2.92 weighted HDDs) while ECMWF remained steady (+0.43 HDDs, +0.55 CDDs), leaving low confidence in the extended forecast for natural gas demand.

Hub-Level Weather

+---------------------------+--------+---------------+---------------+---------------+---------------+
| Hub / Region              | Weight | GFS Cum. HDD  | ECMWF Cum. HDD| GFS Cum. CDD  | ECMWF Cum. CDD|
+---------------------------+--------+---------------+---------------+---------------+---------------+
| Midwest (Chicago)         |  0.35  |     48.80     |     67.26     |     15.32     |     19.85     |
| East (New York City)      |  0.30  |     38.62     |     47.20     |     25.06     |      8.68     |
| South Central (Houston)   |  0.15  |      0.00     |      0.00     |    233.30     |    176.05     |
| Northeast (Boston)        |  0.10  |     95.54     |     85.14     |      9.34     |      6.97     |
| South (Atlanta)           |  0.10  |      0.00     |      2.97     |    112.05     |     61.34     |
+---------------------------+--------+---------------+---------------+---------------+---------------+
| Demand-Weighted Total     |  1.00  |     38.22     |     46.51     |     60.01     |     42.79     |
+---------------------------+--------+---------------+---------------+---------------+---------------+

Key Hub Drivers & Divergences

  • Midwest (Chicago, 35% weight): Serves as the primary driver of national HDD variance. ECMWF is significantly colder, delivering 67.26 HDDs versus GFS's 48.80 HDDs (mean daily HDD divergence: 3.69). The split is most severe on October 15–16, where ECMWF projects mean temperatures dropping to 55.8°F (9.18 HDDs) and 49.3°F (15.67 HDDs), whereas GFS maintains unseasonal warmth with zero HDDs.
  • East (New York City, 30% weight): ECMWF generates more space-heating load (47.20 HDDs vs. GFS 38.62 HDDs). GFS exhibits high-amplitude warmth during the mid-period (October 12–13), averaging 70–74°F and generating 14.04 CDDs over two days, while ECMWF stays near normal (63–64°F, 0 CDDs).
  • South Central (Houston, 15% weight) & South (Atlanta, 10% weight): Southern power-burn demand diverges heavily. GFS projects persistent late-season heat across Texas, yielding 233.30 CDDs in Houston (+57.25 CDDs above ECMWF). In Atlanta, GFS projects 112.05 CDDs compared to ECMWF’s 61.34 CDDs.
  • Northeast (Boston, 10% weight): Boston is the only major hub where GFS is net-colder than ECMWF (95.54 HDDs vs. 85.14 HDDs), spurred by a sharp cold bias on October 10 (10.83 HDDs vs. 2.44 HDDs) and October 16 (12.78 HDDs vs. 1.70 HDDs).

Demand Implications (Natural Gas)

  • Shoulder Season Transition: October represents the shoulder period where cooling demand wanes and early residential/commercial space heating emerges.
  • Bullish/Bearish Balance:
    • ECMWF Scenario (Heating Bias): Accelerates the kickoff of the heating season across the Midwest and Mid-Atlantic. Higher heating requirements (46.51 weighted HDDs) would initiate earlier storage withdrawals or curb late-season storage injection trajectories, supportive of near-month NG contracts.
    • GFS Scenario (Extended Summer/Power Burn): Keeps gas-fired power generation elevated in ERCOT and MISO/PJM via 60.01 weighted CDDs, but defers early heating demand in top consuming markets, keeping early-October balance looser.

Model Agreement & Caveats

  • Convergence Score (0.3159): A convergence score of ~0.32 denotes poor alignment across the 15-day period, driven by a high demand-weighted daily HDD divergence of 2.17. Model confidence in the 8–15 day window is very low.
  • Run-over-Run Shifts: The GFS cycle underwent an aggressive warm adjustment (+7.99 CDDs, -2.92 HDDs), whereas the ECMWF remained consistent (+0.55 CDDs, +0.43 HDDs). When one model exhibits large run-to-run swings while the other remains anchored, traders typically discount the shifting solution until verified by ensemble means.
  • Limitations: Deterministic 15-day point forecasts via Open-Meteo are subject to boundary-layer resolution artifacts and amplified volatility at Day 10+. Market participants should cross-reference this outlook against probabilistic ensemble distributions via the weather stream.