QUITE an amazing number of detailed responses, so thanks.
I found that clicking on the clock in the UI while using the "Rain Accumulation" button, it states as you said, 'a forecast of what the rain accumulatION will be for the next 12, 24, etc. hours/days', (and NOT the rain "accumulatED").
However, when just clicking on the clock while using the more common "Rain, Thunder" button, it says that it will show at least some history: "Rain/snow accumulation in the last 3 hours." Of course, it is only updated every 12 hours at around 4:30 PM, in the middle of our most likely rain period, so it isn't extremely helpful. But, it was showing me some of what I wanted yesterday at that time, right after most of the rain was over.
It seems that if ECWMF has that past history, it is possible that they could make it available for the past 12 hours, instead of just 3 hours, and then present the last 12 or 24 hours of rainfall. That would accomplish most of what I'd be looking for -- a rough estimate of past rainfall.
I have been using a PWS that is about a mile from me from WU, which does an OK estimate. And I agree that I really should put out a gauge, but correct placement away from walls is difficult but vital.
I'm thinking it would be cool to put an unobtrusive gauge on one the side of my mailbox, which is about as is isolated away from obstructions as you can get. Then just check/dump it when getting the mail.