Data fine, interpretation faulty: Why IMD gets forecasts wrong

On January 7, in its three-day forecast, the India Meteorological Department (IMD) warned of "moderate rainfall across central and northwest India" on January 8 and 9 and issued an orange alert for Haryana, Punjab, Delhi, Madhya Pradesh, and parts of Rajasthan, predicting rain and thunderstorms in parts of these states.

January 8 came and went - with no sign of rain in most parts of these states.

Ditto with January 9 (although, after the January 8 debacle, IMD tweaked its forecast to "a possibility of isolated showers").

The problem, experts say, is not the technology or the models - but simply the interpretation of data by weathermen.

Defending IMD's forecast, a senior weather department official said that a cyclonic circulation was developing over the region at the time the warning was issued.

"Rainfall activity has been reported in parts of Rajasthan, Madhya Pradesh and Uttar Pradesh, but it did not reach Delhi and NCR. Such error margins are completely normal and is likely with the best of forecasters," added this person who asked not to be named.

But this was not the first time India's weather office got its forecast wrong. Last month, IMD was also unable to accurately predict the "extremely heavy" rainfall that inundated Tamil Nadu, killing at least 10 people in a span of two days. The state officials mentioned in subsequent press briefings how a warning from the agency could have resulted in better preparedness and less damage.

IMD director general M Mohapatra said, without referencing any specific event, that no weather agency can be accurate all the time and that small misses in the prediction of weather developments such as non-seasonal rains should not be categorised as "mistakes".