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.