Well, I spent a few minutes looking back at WFC and there are quite few days out of the last 20 with very heavy post market trading and it didn't really seem to foretell much about the next day's open.
For example, on the price closed at 28.74 and then in the first fifteen minutes of after hours trading 18,000,000 shares were bought and took the price up to 29.35. The next day price opened at 29.11 and traded down to 27.31.