---
title: "Long Period Average (LPA) of Rainfall: Definition"
description: "The Long Period Average (LPA) is the multi-decade mean rainfall the IMD uses as its monsoon baseline. Learn how 96–104% of LPA defines a \"normal\" monsoon."
url: "https://modeldiplomat.com/learn/glossary/long-period-average-rainfall"
---

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Model Diplomat Research Team · Last reviewed June 22, 2026

TL;DR

- The Long Period Average of rainfall is the mean rainfall recorded over a fixed multi-decade reference period, used by the India Meteorological Department as the baseline for monsoon forecasts.
- What is the current all-India LPA value for the southwest monsoon?
- What rainfall percentage of LPA does the IMD call a 'normal' monsoon?
- Why does the IMD express forecasts as a percentage of LPA instead of in millimetres?
- Can a 'normal' all-India LPA figure still mean drought in some regions?

[Civil Service & Diplomatic Exams](https://modeldiplomat.com/learn/civil-services/glossary)Updated June 22, 2026

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Example

In April 2023 the India Meteorological Department forecast the southwest monsoon at 96 per cent of the Long Period Average, placing the season at the lower edge of the "normal" band amid an emerging El Niño.

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