I have a suggestion about how the rain filter is implemented with respect to setting up alerts.
Right now, an alert will be sent if "at least" the defined amount of rain accumulates in the time frame. What I would like to see is a filter for "maximum" predicted rain fall or rain accumulation. That is, don't send an alert for a site if too much rain is forecast to occur. My use-case is to monitor specific sites to find days that have high predicted winds with minimal rain.
(I've been using the Windy site for a few months now, and I love it!)