[sealaska]

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]

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.

[lbrindze]

GEFS is the noaa ensemble product. The operational GFS is actually just a single deterministic forecast run.

A lot of private providers roll up different agencies models to provide their own proper ie tart weather model because this is a lot cheaper than running the HPC required for most deterministic models.

The most important thing when checking the weather, especially with apps like windy, is to compare multiple models for your self to see how “stable” the forecasts are that day.

[sealaska]

That makes a lot of sense. I sail in SE Alaska.

You'd be surprised how many people make their living on the water up here, but their understanding of forecasting seems to amount to "download windy app"!

Anyways, the word ensemble is new vocabulary for me when it comes to forecasting - things are making more sense knowing what an ensemble is.

[transportguy]

Ensembles aren't used much outside of competition or serious industry... windy/predictwind/CMAP have usually more than enough weather for the average boater

[sealaska]

No argument from me there! But when the forecast completely misses in SE Alaska, or one forecast model displayed in Windy is way different than others, I naturally get curious as to what happened, so have been more interested in the nuts and bolts than is probably practical.

I'm more comfortable on the water knowing terms like ECMFW, myself!