Entry · Water
MLT: Long-term average
What average is the energy reaching the reservoirs compared with?
Acronyms: ONS, National Electric System Operator; ENA, Natural Inflow Energy.
In one sentence
Long-term average: the reference against which the ONS publishes the ENA as a percentage.
Real example
On Sep 28, 2026, the gross ENA of the South was 242.8% of the MLTNature of the data: Observed; over 30 days (sum of ENA over sum of MLT), 253.4%Nature of the data: Calculated.
No Check this number record of its own in this example: the number comes from the panel's published database, which carries the source and the reference date.
Observed: Value published directly by the official or primary source. Calculated: Deterministic transformation made by Scrutiniums, with a published formula.
Why it matters
How it is measured
The ONS publishes gross ENA and storable ENA in energy (columns ending in _mwmed, described in the dictionary as MWmonth) and as a percentage of the MLT. The dataset does not report how the MLT is calculated or its reference period.
Not to be confused with
ENA is the value for the period; the MLT is the reference with which the ONS publishes it as a percentage. The dataset does not report the reference period of the MLT; that is why, in the panels, "above usual" comes from the historical distribution, not from the MLT.
What cannot be concluded
- The calculation method and the reference period of the MLT are not reported in the dataset; readings of "above or below usual" use the historical distribution published by the platform, not the MLT.
Related entries
In the learning paths
Official source
ONSData dictionary of the “ENA Diário por Subsistema” dataset
Literal excerpt from the document
Portuguese only“Valor de ENA bruta por Subsistema medido em percentual por média de longo termo-MLT (%)”
Documents accessed and text checked on Sep 28, 2026.