Three mature S maples on my lot. One has small unfurling leaves, another the buds just swelling, & the third (the largest) shows hardly any activity.

I show the largest behind & to the left of the black cherry when it is fully leafed. Branches down to the ground forming a handsome dome:

You just never noticed before.

I started keeping a spreadsheet several years ago of time of first leaf, flower, and annual caliper of our trees. While fairly consistent in sequence, individuals do vary somewhat in relation to others from year to year. Our "Autumn Blaze" was considerable ahead of our "Autumn Fantasy" this year, while they are typically within about 2-3 days of one another. Sometimes our Commemoration has its first leaf before our Fall Fiesta, sometimes it's the other way around.

Arktrees

You have a good eye hairmetal. I've noticed the same thing, and yes I do think it's more pronounced this year. But maybe we are just noticing more because it seems unconceivable that trees are still leafing out here in early May. (besides Fagus sylvatica 'Rotundifolia', which is always incredibly late and has to be one of the latest to leaf trees of non-subtropical origins. My 2 Dawyck clones are about 2/3rd expanded, while the buds on 'Rotundtifolia', which is in a sunnier spot, aren't even swelling yet!)

I forget about European Beech being fairly late too.

Also Taxodium - the big baldcypress near my office has just some little green nubs showing, whereas the adjacent Metasequoia is almost fully in leaf.

I grew up in Akron, Ohio, and the leafout progress this year as of May 6 here in Central MD is behind even some years in Akron (one full zone colder) from what I remember.

A side thought - although it's been cool, I think the long, cold winter meant that even the earlier-leafing trees were still stone-cold dormant well into March, where many years, at least their "juices start flowing" so to speak in February, so that it doesn't take much additional warmth to break bud.

My understanding is that most species, after their dormancy/winter chill requirements are met, stay dormant until a certain number of "degree days" (accumulated hours over a certain temperature) are accumulated. This year, that process didn't even really START until Mid March to any real degree - most years it probably starts sometime in February or even January.

Even the Acer rubrums around here weren't blooming until about the last of March - sometimes they bloom in February (in January a few years ago, in fact).

I have Azaleas that PEAKED on March 28 in 2012 (a ridiculously warm year, of course) that are just now opening. Most years they bloom around mid to late April.

I will third or fourth the observation of lateness. Watching the black walnuts think about leafing out is an exercise in patience. I am trying to guess if exposure or some health issue decides if a tree leafs out earlier than others.

"meant that even the earlier-leafing trees were still stone-cold dormant well into March"

Yes, my Prunus mume were actually *more* than a month later than they have been in early years. It has bloomed as early as late February, this year it bloomed in early April. However we are catching up in the sense that the later something blooms the less it is affected. My early rhodies like 'Mt. Siga' are almost 2 weeks late but I think the late ones like 'Vulcan' will just be a week late if that.

Plus the 80+ temps forecast later this week will help (and the long-range seems to suggest our highs staying above the mid to upper 70s).

The red maples do this too, but that I notice every year.

It seems certain trees are prone to produce ridiculously heavy seed crops to the point where even now, as the samaras are almost mature, there are just barely some emerging leaves showing. I seem to remember that even in summer, the trees that had the heaviest seed crops never really create a dense leaf canopy that year.

Anecdotally, of the most common cultivars, it seems 'Red Sunset' produces much heavier seed crops on average than 'October Glory'.

After what I thought was rather cool winter for central Texas, I was surprised to see that Mexican Sugar Maple at my parent's in law's starting rather early. Same for my Montezuma cypress that started growing in early February. (yes, that early). I was like "please, no late hard freeze". Of course, that happened a month later which was rather unusual as it doesn't get that cold that late.

And yes, that maple got zapped by late hard freeze.

Bizarre. Never saw that living 180 miles further to the north for 10 years for such late hard freeze.

Oh no! I just posted about my Sugar Maple not leafing out yet, and that the neighbor's Sugar Maple already has. I didn't realize that "Acer Saccharum" was a sugar maple.

I can't delete the post I just made, but it's nice to read your post and see that there are indeed variables from tree to tree in leafing out.