I'd first consider Pseudomonas.

Here is a link that might be useful: Maple -- Bacterial Leaf Spot and Dieback

I've not seen the branches go black, only grey (and dry) at ends but who knows how long they are black before they go grey so perhaps I didn't notice it?

Cover with a portable greenhouse to prevent typical dieback?

Dan

Same site has multiple other pages on various maple problems seen in the region.

A certain amount of dieback is to be expected. But this is typically just the odd branch end or smaller twigs here and there. If there is a significant amount of dieback, then it may be the problem is not related to normal growth patterns or weather/cold damage but to some other cultural condition or disease pathogen.

Without seeing exactly what kind of damage we are talking about, we are just speculating on a) it is normal or b) the symptom of something more pernicious.

In Redmond, they might put it something like: some dieback is a feature, not a bug. More than typical could be any number of things.

Dan

If your soil is thin and you didn't water last summer, might be a factor for more than normal dieback. Down in the Puyallup Valley, where the soil is heavier,that would be less of a reason.
Mike

Soil is nice, not too sandy and not too clay. Some of the Japanese Maples have no dieback at all, some have maybe 4-6" dieback at end of branches.

I have a drip system so summer droughts aren't a problem.