Journal of Climate, 19, 6025-6046

Predictability and prediction of European monthly to seasonal climate anomalies

Mark Rodwell and Francisco J. Doblas-Reyes
ECMWF, Shinfield Park
RG2 9AX, Reading, UK

Numerical weather prediction (for Europe) has a tangible benefit to users. The analysis of the initial atmospheric state is important for the success of these forecasts. Climate change forecasts are also of benefit to users such as politicians. Radiative boundary forcing plays a key role in these forecasts. This paper investigates and reviews intermediate timescales where European predictability may rely on both the initial conditions and quasi-boundary conditions associated with (e.g.) SST and soil moisture. Operational probabilistic (ensemble) forecasts indicate skill in the prediction of the European summer heatwave of 2003 on medium (3-10 day) and monthly (10-30 day) timescales. A more general and unified analysis of medium-range, monthly and seasonal forecasts confirms a surprising degree of probabilistic forecast skill for European temperatures over the first month. Interestingly, the unified analysis suggests that the initial atmospheric state is important even for month two of a seasonal coupled forecast. This is later confirmed by experiment. Seasonal deterministic forecasts appear to capture the observed European predictability associated with the persistence of anomalies. Multi-model and perfect-model studies are used to highlight the potential sources for improved seasonal forecasts. Finally, the impact of forecast information on different users with different mitigation strategies (i.e. ways of coping with a weather or climate event) is discussed. The possibility that weather forecasts can affect the cost of mitigating actions is considered. The simplified analysis leads to different conclusions about the usefulness of forecasts which could guide decisions about the development of "end-to-end" (forecast-to-user decision) systems.

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