Supposedly due to the downing of a Russian fighter jet, stock futures are well off from their close on Monday. At their worst, S&P futures were down more than -1% but have since recovered.
So far in 2015, there have been 27 days when the S&P opened down at least -0.5%. Table 1 shows the short-term results going forward.
For the remainder of the day, stocks tended to remain weak, gaining from the open to the close only 9 times. Returns steadily improved, especially looking out over the next week.
In the history of SPY, there was a gap down sometime within 5 days of Thanksgiving 10 times. Again, open-to-close returns were weak, with only 3 winners. But a week later, the S&P was higher 9 out of the 10 times.