When KY reports its results, note the margins in its rural counties. In 2016, the bottom really fell out for Hillary in rural KY, which in retrospect was an early indication of trouble for her nationally. If margins in those areas return to 2012 levels (or further left), that would be a good sign for Biden.
Atlas Favorite Elliott County is actually a good indication here: it's small and counts quickly, and while Trump is obviously going to win it, if he only gets, say, 60% instead of the 70% he got last time, it's a disastrous sign for him because it means he's losing ground in similar areas in PA, & NC where he can't afford to lose a single vote.
