EFI and Shift of Tails (SOT)

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I'll try to do this justice.  Someone with a degree or at least more knowledge can correct me - no shame here.  This is complicated. 

EFI is a tool used by the ECWMF to gauge how extreme an event is being forecast by it's ensembles.  One big caveat here - the model is looking at how extreme an event is compared to model climate characteristics.  So if you tend to get a lot of wind, snow, rain, etc, this forecast will shift it even more extreme.  Using rain as an example, a 1" qpf event in FL might not register at all.  On the other hand, if you have little precip, say in AZ, then a 1" qpf event might be considered extreme.  But if you saw an extreme signal for qpf in FL, where perhaps the model climate is say 2.5" it might be a 5 or 6" rainstorm.  These are illustrative only, don't try and do the math on me.  

The shading represent the number of ensembles predicting an event either at over 90% of the climate model. Example:  if the climate model has your area at temps of 40-50 degrees, with 40 being in the lowest 10% and 50 being at 90%, and you are in the .7 to .8 shade, then 70-80% of the members are showing an event at the top range of the climate model. 

The EFI only goes up to the maximum amount in the climate model, so SOT was added to show how far deviated the ensembles are.  Anything positive indicates  how far forecasts above the climate model max.  Anything over 1 is notable.  

 

Info on the EFI can be found at the links below.  The learning center from the ECMWF is a great class to sign up for. 

http://mg.phys.uni-sofia.bg/projects/Banya/presentations/IvanTsonevsky.pdf

https://www.atmos.albany.edu/daes/atmclasses/atm401/spring_2016/ppts_pdfs/Zsoter_2006_extreme_weather_forecasting.pdf

https://learning.ecmwf.int/en-US/web/introducing-the-extreme-forecast-index-efi

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Here's a decent quick youtube overview.

 

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This one is longer.  EFI starts at 46mins. But the whole video is on what products the ECMWF offers.

 

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This discussion of a heat event looks at using the EFI for that event and. has a general description of how it works.  Also describes the NBM.