The Prediction Graveyard
Made with ❤️ by Aniruddh JangidLinkedIn
The Graveyard / India Meteorological Department

resolved · Honourable Graves

IMD forecast all-India June–September 2019 rainfall at 96% of the long-period average, with ±5 percentage points model error.

Source-backed summary; not presented as a verbatim quotation.

India Meteorological Department
National meteorological service · India

Made: 2019-04-15Resolved: 2019-09-30
Original conceptual trajectory diagram illustrating No cause of death assigned
Reasoning and outcomes. Original illustration for The Prediction Graveyard. Aniruddh Jangid, 2026. Original digital diagram. CC BY 4.0. Changes: none. This is a conceptual diagram, not an archival image.

The world at the time.

IMD used statistical and dynamical ensemble models and published uncertainty. Its April outlook anticipated weak El Niño and development of a positive Indian Ocean Dipole.

IMD first-stage 2019 monsoon forecastIMD monsoon 2020 review, reporting 2019 outcomeSkymet 2019 monsoon forecastThe Extreme Positive Indian Ocean Dipole of 2019 and Associated Indian Summer Monsoon Rainfall Response

What happened.

The season produced 110% of the long-period average. That was 14 percentage points above the central estimate and 9 points above the upper error bound.

IMD monsoon 2020 review, reporting 2019 outcome

Predicted vs actual.

MetricPredictedActualVariance / caveat
Seasonal rainfall (% LPA)96 ± 5110+14 percentage points versus midpoint; +9 above upper bound
IMD monsoon 2020 review, reporting 2019 outcome

The counter-signal.

Skymet’s April 3 forecast put rainfall at 93% and favored a below-normal season. This contemporary disagreement challenged confidence in a normal season, although Skymet also missed the eventual wet outcome.

Skymet 2019 monsoon forecast

Verdict.

Reasoning: sound · Outcome: wrong

The numeric central forecast and stated error band failed. The sound rating recognizes transparent models and uncertainty, not a claim that one miss proves or disproves calibration.

Official original forecast and official outcome corroborated. Error is calculated against the published 96 ±5 interval; counter-forecast was not vindicated.

Cause of death / explanatory lens.

No cause of death assigned

The lesson.

How should a forecast change when interacting ocean drivers can reverse the late-season trajectory?

Sources.

  1. IMD first-stage 2019 monsoon forecastprimary · 2019-04-15 · claim/date/method
  2. IMD monsoon 2020 review, reporting 2019 outcomeprimary · 2020-10-01 · outcome
  3. Skymet 2019 monsoon forecastprimary · 2019-04-03 · contemporary counter-signal
  4. The Extreme Positive Indian Ocean Dipole of 2019 and Associated Indian Summer Monsoon Rainfall Responseprimary research · 2021 · causal explanation

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