What are the chances the 'puddle' has reached the chick at some point? - I try not to wonder but there it is in my head. 
Even if the water goes down, once the chick is wet....... 
- TPC you know the makeup of the Ledge - any chance the puddle could drain without having reached underneath Princess? ie does it run down the sides into the drain, or just spreads all over?
The corner where Princess is this year is actually a little plateau of small and larger gravel. There is another scrape nearby which has had water in it at least once today but it drains out quickly down through the gravel. For the chick to have gotten wet, the water level would have had to come all the way up beneath the scrape and I can't say that I saw that happening, but my camera angles are pretty much the same as yours. There is another little higher spot at the front of the ledge (near the point) that I don't think is as high as Princess' plateau and it looked fine - wet from above but not from below.
Another concern for our first Radisson chick is that s/he hasn't been fed alot over the last couple of days. S/he can't eat much at a sitting so there has to be hours between feedings, but given a choice between hungry chick and wet chick it seems that Princess has rightly chosen hungry chick. Now when is hungry not a safe thing for a chick this age, I'm afraid I can't tell you. So it may be that the rain may indirectly harm the chick because Princess can't get off him/her to feed without putting him/her at risk of getting wet.
Only time will tell folks. First thing is for the rain to stop long enough for Princess to get food in him/her - even tapering off to spitting might be good enough for Princess to take the risk. Come tomorrow, if the chick has survived, then s/he can make up for lost meals over the weekend and I'm sure his/her parents will be only too happy to oblige.
Rainfall rate continues to fall ...
