If you're on the webpage, under the top left corner hamburger menu the first item is "Donate". Not sure how they've done this year, their goal listed is $550k but for me it shows 0% which I find hard to believe in December. I blame my browser lockdowns.

They also have apps with in-app purchases to donate as well.

My preferred weather widget on Android (Meteogram Pro) links out to Windy if you tap the top center of the widget, it's very handy.