
The icon basically suggests that any remotely plausible configuration of seasonally-appropriate weather (excepting perhaps tornado winds and the second plague) could occur in the next 24 hours - the meteorological equivalent of throwing up your hands, shrugging your shoulders, and uttering "uhnnnnnnuhha?"
Well, my friends, I am sorry to report this, but it gets worse.
Today Google tells me that the forcast for today is "uhnnnnnnuhha?", the forecast for tomorrow is "uhnnnnnnuhha?", but the forecast for Friday . . . well that can only be characterized as this:

Wait a second . . . what the hell is that??? Let's look at these icons side-by-side:

What is different here? Isn't it obvious?! Today and Thursday, we're gong to get some sun, and then a large, ominous cloud might appear, and then some pointy, fast, sky darkening rain might fall out of the sky, whereas on Friday, we're going to get some sun, and then a happy, fluffy cloud might appear, and then some fat, widely-spaced, sky-color-neutral rain might fall out of the sky. Dress appropriately, kids!
Update: Mandy helpfully suggests I use Weather Underground instead. While I'm too lazy independently check the weather each day, I do appreciate this site's willingness to admit they have no fucking clue about the very subject they're supposed to report on. Witness:
I wish I knew about this icon when I wrote my first post on Google weather. Somehow, this is actually more reassuring. Also, their cloud has a mouth, which I like.