Broadwings never do what they're "supposed" to do. Despite the early date, yesterday Hawk Mountain counted over 7000 broadwings, the fifth largest count ever. A few miles to the east at Bake Oven Knob, over 4000 were counted. I only saw one other site that counted over 1000 hawks, the other 30+ sites I checked results for rarely had over 100. So what's going on??
Also, though the wind was largely calm (which broadwings like), when there was a breeze yesterday it was from the south (which broadwings hate). Wind from the south means these birds are moving with a headwind, which means they have to use more energy on their already long and arduous trip down into central and South America.
Interestingly, to me, the Great Lakes hawkwatch sites that often count broadwings in the tens of thousands really haven't seen much yet. In other words, their broadwings so far seem to be arriving (or not) on schedule. So why so many birds in the east this early in the season? Boy, don't I wish I could answer that one.
So I'm going to make a few semi-educated guesses. Although the weather will block migration for the next 3 days, the front is supposed to clear out by Friday and have good skies for flying after that. On the surface of it, the birds shouldn't need to fly in these numbers this early. Something else must be making them want to move early. That something else, in my opinion, is likely food.
I suspect that their food source in the north either wasn't as plentiful as usual, or perhaps it's been cold up north so their food source is vanishing earlier than usual. It's liable to take weeks/months to get a reasonable answer to this mystery. But trying to figure out the "whys" of migration is one of the reasons I find it so fascinating.