I do really well with blacks when the season comes early, but has cooler nighttime temps.
I live in NWI. 3 years ago was a normal season (started to really pop the last week of April), and I'd say I found maybe 100-120 blacks in my usual holes.
The next year was early (first find on April 11th or 12th), but the cooler nighttime temps lingered into May. Those exact same spots produced easily 300+, and for longer than normal. I was still finding new ones almost every day the yellows were up.
Last year was a late year, and I found less than 100 blacks. It didn't help that last year scorched the ground that harbors them. We had cooler temps, then that week of 80s/90s that killed everything over-exposed to the sun...nothing, not even weeds, grew in those patches the rest of the spring. In one spot that I found close to 100 2 years ago, last year I only found 5.
Trees that wake up and develop sooner tend to hold them. I always talk about how I love hunting ash trees, because that's where I find a good portion of my blacks during early seasons (greys too).
Also, I find them in areas with slightly more light exposure than greys and yellows. The ground is usually colder, so they need to absorb extra light to make up for it, hence the color.
Hope this helps