New York City is NYISO’s load zone J, identified as N.Y.C. in the public files.

Two different measurements

Electricity demand is actual zonal load in megawatts. Implied marginal emissions (IMER) are NYISO’s modeled CO₂ emissions per additional MWh, preserved in the source unit of tons/MWh. We do not convert this to average carbon intensity.

These feeds do not provide an NYC fuel mix, consumption-based emissions, or borough-level measurements. The city outlines are geographic context, not a surveyed electrical boundary.

Day-ahead forecast

P-71 publishes hourly marginal emissions for a delivery day from the day-ahead market. The emissions timeline extends from observed data into dashed forecast hours. Forecasts are included only after the latest real-time reading; missing intervals remain gaps. Selecting a forecast hour shows its delivery date and publication metadata. Latest returns to the newest real-time reading. The optional comparison overlay preserves today’s forecast for elapsed hours. Orange is the hourly forecast; green remains the individual observed readings. Hover tooltips summarize the arithmetic mean of available observations within each forecast hour and show the sample count and times. That mean is not time-weighted, and partial hours or missing observations can affect it. The downloaded publication may have been revised; it is not an immutable yesterday-issued vintage. “NYISO updated” is the index’s Last Updated field, not an independently verified original issue time. Recent files were posted around 9:34 a.m. Eastern the prior day; this is observed timing, not a guaranteed deadline. Today’s delivery forecast (published yesterday) and the latest published delivery day are loaded every five minutes. This supplies the remaining forecast hours today and tomorrow when available. Each day retains its own source and publication timestamp. An expired forecast stays labeled with its original date; an unavailable forecast is never filled with real-time values.

Automatic updates

The Node server checks NYISO every 5 minutes while running; this screen checks the server every minute and when you return to the tab. Each check rediscovers daily files, including at midnight, and combines the latest two days into up to 24 hours of observations. Publication delays can occur. Readings older than 20 minutes are marked delayed.

On failure we retain the last successful readings. A bundled, dated NYISO snapshot is used only if no live fetch has succeeded. A saved snapshot is never labeled live.

IMER is informational and based on NYISO’s methodology and assumptions. During the autumn clock change, IMER timestamps lack an explicit UTC offset; repeated local times are deduplicated using the earlier Eastern offset. Actual-load timestamps include EST/EDT.