I have had several dreams of this nature.
About 2 weeks after my mother died (in 1996), I had a dream that she was at a large table sharing conversation and a meal with friends and family. I could watch everything that was going on, but I was separated from them by a glass wall.
In my favorite dream to recall, Mother came striding up the walkway to my house, raised her arm and pumped her fist. She was obviously happy about something! Three days later, my brother (executor of her estate) called me to say that he had a very good offer on Mother's house. It was sold!
The worst dream, but most prophetic, that I had, was one in which my Mother was standing in a spotlight, wearing a long gown. My father was behind her, he was comforting a weeping woman. Mother said "I am sorry, I am so sorry." Then I dreamed that I was having surgery but the doctor could not put everything back properly. When I woke up, I was terrified. I thought I was going to die. But - 2 weeks later, I got a phone call, and my cousin had been diagnosed with ovarian cancer. The doctors could not operate. I realized the weeping woman in my dream was my aunt, mother of the cousin with cancer. It happened that my cousin died about 6 months later.
So - the dead know what is going to happen to us?