Abstract
Forecasting heavy precipitation has an important role in mitigating floods and associated hazards, but it remains one of the main challenges in operational meteorology. Our previous study confirmed the close connection between large-scale extreme precipitation events and anomalous moisture fluxes in central Europe.
In this study, we introduce a variable accounting for the accumulated ascending moisture flux, which could potentially support extreme precipitation event forecasts. The variable reflects the total amount of transported water vapour in combination with extra high upward vertical velocity, which are important factors required for extreme precipitation occurrence.
Looking at ERA-Interim forecasts, we aim to determine a practical predictability and forecast skill of accumulated ascending moisture flux and compare it with the forecast skill of precipitation. While the predictability of moisture flux itself is satisfactory, generally less accurate forecasts of the vertical velocity negatively affect the predictability of accumulated ascending moisture flux, especially in the case of summer precipitation events with prevailing northern moisture flux.
Nevertheless, the forecast of the proposed variable was adequate and stable up to 6 days in advance in all cases of maximum events that produced major central European summer floods. There were no such stable forecasts for less extreme events or false-alarm precipitation extremes.
Thus, we hypothesize that the calculation of the accumulated ascending moisture flux from numerical weather prediction could be useful as a supporting tool in extreme precipitation warnings in central Europe.