I've read a lot of questions about the specifics of meteor impacts on this site, but strangely this one seems to still elude me:
Assume a meteor of sufficient mass and speed to wipe out human life within a week (if not sooner) impacts the planet. What does this look like from the perspective of a person on the ground? No real change until instantaneous vaporization? Death by a massive shockwave? Localized devastation followed by a slow collapse to environmental causes?
To be specific: from the moment the meteor is seen by the naked eye to the extinction of life on the surface, and from the perspective of a human observer, what happens in what order?
The impact in question happens over land, and at a roughly perpendicular angle; the observer is able to see the impact site at the edge of the horizon assuming they're elevated no more than a storey above flat terrain.