If the weather is severe enough to delay ground traffic, what are the odds that a drone will be capable of flight/navigation? A full-sized, manned aircraft has fairly specific limitations (crosswind, turbulence, etc.) within which safe operation is possible. While there's at least one less life at risk (the pilot's), I can only imagine that current drones are even more tightly limited - not so much by legislation as by simple physics. If your aircraft has a maximum airspeed of 20kts, any wind exceeding that automatically grounds your drone fleet (unless you're into one-way missions). I've always nursed a pet suspicion that this is what caused John Denver's death - he was flying an ultralight; if the offshore winds ("Santa Anna", I think?) exceeded the maximum airspeed of his ultralight, he probably spent the last few moments of his life watching the shore get further and further away - with no way to rescue himself or radio for help (I don't believe ultralights carry an aviation comms stack).
