Saturday I noticed that a large oak with a pronounced lean in the direction of the house and the power line and recently cleared of nearby underbrush, had serious cracks running up from its base. Checking the base closely showed that in addition to the large vertical cracks, a large root on the side away from the lean had snapped under the strain. I called the first tree service referred to me by a neighbor: he arrived in an hour, said it was dead and should come down. He quoted me a price for a two-part drop, taking the top off first so as to avoid risk to property, clearing and chipping of branches, and said he'd bump a non-emergency client to come Monday. Assured me there was "absolutely no worry" about it coming down in the next several days.
Monday morning he called on a half-hour's notice for a 9am appointment to say it's raining, he doesn't like to climb trees with chainsaws in the rain (a perfectly sensible attitude, of course) and wasn't coming until Tuesday morning. Rain cleared by 11:30am and the afternoon was mostly blue sky from noon on.
Monday afternoon I came home, looked, noticed the root crack had widened from about a half-inch to over an inch and the fissures on the trunk seemed wider. Called the professional to tell him the cracks in the root and in the trunk were larger than before. His response: "Oh, they were pretty large Saturday." Yes, and they're more so now. He told me it absolutely wasn't coming down on its own tonight or over the next several days without a strong wind storm or a major ice storm, neither of which was forecast - and neither of which happened. We moved our cars out to the street as the oak's drop path was across where they normally stay overnight.
It fell about five hours later. The oak was rotten at the base and snapped about 12' up, so its arc was shorter than I'd estimated. No one and nothing was damaged.