In current Windy Alerts implementation, there is a possible (of course ugly) workaround for people who want alerts for "no rain", or for "rain less than": just set an alert for e.g. "At least 1mm must accumulate". Here, receiving no alert at all would mean "no rain above 1mm"... Of course this is not the right usage of alerts, but it should work (the odd way)...

About 2 conditions for the alert settings: yet another workaround would be to set 2 different alerts for two different positions on map which are enough close each other...