The forecast weekly surplus data is also known as OCNMFW - Forecast Weekly National Surplus based on OC2. It is part of the 2-52 week forecast produced each Wednesday by the System Operator as required by section 4.1.2 in Operating Code 2 of the Grid Code.

The process used to calculate the Surplus is analogous to that used to calculate the Forecast Surplus Day (SPLD) figures in the 2-14 day forecast.

The Surplus figure published for each week in the 2-52 week forecast is thus a half hourly average MW value for the half hour in the week which is forecast to have the highest forecast demand.