Plot extreme for probabilities

Hi @abatalla,

As discussed yesterday, we need to add a development to ensure that SUNSET displays the probabilities of exceeding (or not exceeding) a threshold.

To simplify this development, I agreed with @vtorralba that a good approach could be to use PlotEquiMap. It may be worth it to consider the plot_ensemble_mean function() as a starting point, which already creates the titles and includes the colour palette:

In this case, probabilities are adimensional ranging from 0 to 1. The development should be flexible for any probability threshold. I think the colour legend must also be flexible. Although the range is fixed, the probability threshold impacts the interpretation of the results. But we can work on this later.

In this case, if we want to mask (or stripe) the non-skilful gridpoints, we will need to use the corresponding brier skill score which should be computed early in the workflow.

We can discuss this on Monday or organize a specific meeting for this if you consider it necessary. Please, don't hesitate to contact me for any clarification you need.

Cheers,

Núria

FYI @vagudets