I don't have the whole scene before me when I'm writing a story. I start with an idea and consider the back ground plot. But once in the story, `walk into it and look around' checking the weather and terrain to see what my characters are facing and dealing with. Also allowing the characters to take over their story according to the personalities I have given them.
And if you are writing an informative blog, it's not all imagination, it's also relying on personal experience and knowledge gathered over the years and being aware of people's needs..