Windy.com uses the "INTERSUCHO" system from the Czech Hydrometeorological Institute. Here's the paper: https://www.mdpi.com/2073-4433/12/7/913

There's a website (it's in Czech): https://intersucho.cz/

Windy.com, being developed in Europe, often uses European datasets.

Looks like windy.com is showing short-term trends, perhaps driven by things like “how long since it last rained”, etc. Michigan is showing severe drought, and then you set the date to the 12th and it all clears to normal (there’s rain in the forecast around then.)

It’s a lot different than the long term trends driven by total annual precipitation, snowpack, etc.