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shoyer | 4 years ago

ECMWF makes probabilistic forecasts, in the form of an ensemble of 50 IID examples. So this is mostly matter of Windy figuring out how to put that information into their UI.

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sealaska|4 years ago

Thanks for the reply. It sounds like you have a much better grasp of these things than I do.

So, when clients like windy forecast "10 knots east gusting to 20" for ECMWF, do you know if those numbers are directly copied and pasted from the ECMWF model, or do clients take the probabilistic forecast model and make some sort of average prediction that they display?

I'm very interested in how clients like windy go from a probibilistic forecast model to a singular hard number. Unless this is something built-in to ECMWF itself.

transportguy|4 years ago

GFS takes a simple average of the ensembles for their avg model, I believe. The biggest problem is that you can't use statistics like you normally would in meteorology. Predictions are actually very good for knowing WHAT happens to a weather system, but not WHERE it happens.

I work in the sailing space, so this is what happens there:

A racing offshore sailor would consider a variety of models and ensembles. Then they would consider the various possibilities for the weather systems and fronts (e.g. front crosses your path +/-5% East/West within a +/-3h gap). A sailor would then avoid any possible dangerous situations, and pick a path that on the most number of models gives them an optimal wind.

It is both an art and a science. If you compare the results of sailors who compete in offshore competitions (such as the Vendee globe), where the boats are all constructed in very similar ways, you'll see that the best sailors consistently get good results, and that is based on good meteorology and a good gain to risk ratio for route choice.