An Investigation of the Limitations of Ensemble Precipitation Forecasts

Ensemble forecasting techniques are vital for accounting for the chaotic nature of the Earth's atmosphere. In order to better understand and use ensemble forecasts, the THORPEX Interactive Grand Global Ensemble (TIGGE) database was created, consisting of ensemble model data from the leading meteorological agencies of the world. Using data obtained from the TIGGE archive, two cases were selected in which the ensemble of the European Centre for Medium Range Forecasts (ECMWF) underestimated the magnitude of the forecast uncertainty. We compared the ensemble spread and the forecast uncertainty for total column water and total precipitation for both cases. In the first case, the ensemble underestimates both the precipitation and the total column water forecast uncertainty for a low-pressure weather system in the western pacific. In the second case, the ensemble also underestimates precipitation and total column water uncertainty in association with a mid-latitude cyclone affecting the southeastern United States.