Seasonal Normal Weather Review 2025 - Impacts to AQ

As also explained in the June news article, the introduction of a new Seasonal Normal Weather basis will impact the calculation of Annual Quantities (AQs) and, owing to the increased warming, you can expect AQs to reduce as a consequence.

The implementation of a SNWR requires certain key parameters, used in the AQ calculation, to be re-stated for historical Gas Years in order that they reflect the new basis.

Customers who mimic Xoserve’s calculations of Class 3 and 4 Supply Meter Point Annual Quantities (AQs), and/or Read Estimation processes, will need to be aware of the following:

Class 3 and 4 AQ calculations

The formula for calculating the AQ is unchanged, however AQs calculated in September 2025 with an effective date of 1 October 2025 will use re-stated Weather Adjusted Annual Load Profiles (WAALPs).

If you replicate the AQ calculation in your own systems, you will need to ‘refresh’ your historical WAALPs using the re-stated values. For AQ purposes we have published the underlying components of the WAALP calculation (ALP, DAF, CWV and SNCWV) for Gas Years 2021/22 to 2024/25. (AQ calculations in September should not use meter readings earlier than this).

Details of where to find the re-stated parameters for the WAALP calculation can be found in DESC's Seasonal Normal Review 2025 overview document (section 3 slide 20).

Those Supply Meter Points that have not had a successful AQ calculation during the September AQ process will have a Seasonal Normal Ratio applied to it. The Ratios are applicable at End User Category (EUC) level and the final approved values were recently shared at DESC (slides 9 to 18).

For Shippers and Transporters, details of the Supply Meter Points where the Seasonal Normal Ratio has been applied will be viewable in your NRL* and NNL** files, provided to you around 22 to 23 September. These files will contain details of the revised AQ value and new EUC.

*NRL files: For these Supply Meter Points there will be no start and end dates/meter reads populated in the T04 record and there will be an additional T98 record (AQ Calc Failure) with the failure reason code.

*NNL files: For these Supply Meter Points there will be no Formula Year information in the A92 record.

Class 3 and 4 Read Estimation

In UK Link there are several scenarios where read estimation is necessary, such as opening reads when there has been a supply point transfer. Although the formulae used for meter read estimation is unchanged, it does utilise the WAALPs when performing the calculation of energy and this could cover a period which goes back to April 2019, hence we have also made available underlying components of the WAALP calculation (ALP, DAF, CWV and SNCWV) for an additional three Gas Years: 2018/19, 2019/20 and 2020/21.

Xoserve System Updates

Please note: from Wednesday 27 August 2025 (and daily thereafter, until 1 October 2025), the current historical WAALPs in Xoserve’s systems will be replaced using the re-stated WAALP values in readiness for the AQ calculation on 12 September 2025.

Any subsequent read estimation calculation performed by UK Link from 27 August 2025 onwards will utilise the re-stated WAALP values.

Further information

You can find a high-level summary of the Seasonal Normal Weather Review so far on the dedicated Demand Estimation Sub-Committee webpage on the Joint Office website. 

If you have any questions or comments on the Seasonal Normal Weather Review, please raise a Support Request here and your query will be directed to the Demand Estimation team.

Raise a Support Request