The Gaussian Mixture Model (GMM) incorporates various data inputs to support the Day-Ahead Ancillary Services Market. Among those inputs, it was anticipated that the GMM would use the most recent gas day price available. While the ISO determined that is best calculated using the Algonquin Non-G gas index, the most liquid gas traded in New England, the ISO realized there was a one-day lag in the gas price index pulled for the analysis.
Therefore, effective September 12, 2025 (for the operating day of September 13, 2025), the ISO will update the process and timeline to use the most recent gas day price available, specifically the next-day gas price from the previous trading day. For example, a GMM run on a Wednesday for the Day-Ahead Market for Thursday will use the gas-day price available on Tuesday at 6 p.m., rather than the data from the day before that, or Monday in this example.
The impact of this adjustment was and is anticipated to be minimal. Nevertheless, the ISO wanted to notify participants of the adjustment to the timeline for the gas price index used in the GMM runs, particularly as it looks ahead to the winter period, where a more current price will be helpful for the analysis.
