I believe this is another related, simililar, yet technically different phenomenon, with different causal mechanisms, but yes, lets keep adding to the list, lol.

Also, brb, you'll never believe this, apparently my pizza delivery guy's name is 'Hiro Protagonist', he's almost here, and I gotta ask him what is up with that name.

Visual snow is different, it's constant and looks more like tv static or film grain, fun stuff, not.

I mean, now maybe, lol, but I noticed this as a middle schooler, and I was in pretty good shape back then... and I still have the exact same experience to this day, in the right lighting conditions, if I can just sit or stand still and look at a mostly cloudless sky.

The dots are white blood cells moving in the capillaries in front of the retina of the eye.

From the wiki page.

So, yeah, it makes sense that very similar or even just the same effect can be intensified by all those things you mention, they all alter the motion of blood in your eyes.

As to a big chunk moving?

I am not an eye expert, but I would intuitively think that yes, a big splotch moving could be the retina itself moving... but it could also potentially be something like a clot in one of those capillaries breaking loose... which is probably still bad, but maybe not necessarily as bad?

Basically, lighting conditions have to be just right to ... basically, allow you to actually see your own white blood cells, in your own eyes, against the ... background/everything you are seeing.

So my guess would be that in the summer, where you are, the ... ambient light of the sky is too bright, it overwhelms this effect, but in the winter, maybe its mote generally humid, or the light is coming through more atmosphere , at more oblique angles, and is thus less intense.

Though if you are also seeing a... black tail, like... they're followed by a black smear or a motion blur or something... that could be something else?