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Ensembles are well equipped to forecast the first two types of anomalous events with the current resolution.   Extreme  Extreme convective features are less well captured but can, to some extent, .  But a risk assessment can be added by experienced forecasters , or via statistical interpretation schemes.

The Extreme Forecast Index (EFI) and Shift of Tails (SOT) have been developed to show forecasters how ongoing weather  highlight event probabilities relate to time-of-year dependant climatological conditions at every location.   in relation to climatology for each location and time of year.

EFI and SOT parameters for CAPE and CAPE-shear have shown some noteworthy skill in foretelling of severe convective events that the IFS itself cannot predict be predicted directly by IFS itself.

These parameters have some general applicability for EFI and SOT parameters aid impact forecasting as they indirectly relate to local return periods for different types of adverse weather.  Forecasters   Forecasters can also benefit from an understanding of the local resilience of man-made infrastructure in the face of natural hazards.

The forecaster’s role

Considerations of probability, jumpiness, and the forecaster’s role apply in particular to extreme weather forecasting.  Calibrating  Calibration or otherwise applying statistically based modifications to extreme weather events is very difficult because of their rarity.  However, forecasters can accumulate some experience of the capability of IFS models’ capabilities from models from extreme weather events in neighbouring areas.  Complementary information, in particular particularly forecasts from different other NWP models and/or IFS runs, might motivate forecasters to upgrade or downgrade the probabilities.  Forecasters also have a unique role in supplying can also supply probability forecasts of events that are not explicitly covered by the ECMWF forecast products (e.g. thunderstorms).   

Perhaps the most important task is to help end-users , (such as regional and national authorities, ) to make the optimal decision about protective action.

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Severe or extreme weather is often characterized by low protective or insurance costs compared to high potential losses.  Thus relatively low probabilities can become highly decisive.  Using a cost-benefit approach can help the forecaster to enhance advice to the customer.  Protective action might be prompted at a level as low as 10% event probability, or even lower.  Forecasters’ advice

Advice does not have to be probabilistic; if they .  Purely categorical guidelines may be developed if forecasters are very familiar with their customer’s decision process and preferences, purely categorical guidelines may be generated.   In cases of extreme weather, the necessary actions may be obvious - .  This might be evacuating the area or taking shelter but .

But in the end the decision to advise on and/or enforce major actions such as these will probably generally be down to the customer._{Updated/Amended 30/12/19 - Simplification of High Impact Weather}