system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What’s keeping weather forecasting from being a highly accurate science?

We’re expecting snow where I live and forecasts vary wildly. So, what’s the roadblock keeping meteorologists from being far more accurate? 
(No snark or judgment on the profession here, truly curious)
gpt
There are an insane number of variables. Whether the air is over water or dirt or rock, how hot that is, what direction the wind is blowing, what direction it was blowing yesterday, the temperature *here*, the temperature *there*, the pressure here, the pressure there, the elevation here, the elevation there, what kind of vegetation is growing, the season, how active the Sun is, what time of day, how humid it is, how humid it *was*, what the temperature was like yesterday, what the temperature was like yesterday over there, how much dust is in the air, has a volcano erupted, is there a forest fire etc. etc. Every single point *on Earth* affects every other point, so that the variables for the next county over in every direction are affecting what's happening in your county; except, what's happening to the counties next to *them* affects *them* which affects your county. Except the Earth is a sphere, so what's going on in your county is affecting the counties that are affecting the counties that are affecting the counties and so on that are affecting your county.

The weather is affected by the ocean currents, too. Like, a lot. And all of the variables that affect the air above the water are analogous to variables affecting the "weather" of the ocean currents in the water, like the topology of the ocean floor, the temperature, the salinity, etc. So you have to do all the same work twice, so that you can predict what the ocean is doing so you can predict what the air is doing.

And of course, the air also affects the ocean! So you have to predict what the air is doing so you can predict what the ocean is doing so you can predict what the air is doing.

Everything is interconnected and complicated and it's an entire planet's worth of data to sort through, and no two places on Earth are exactly the same. So you can model what happens tomorrow with some reliability, because it does take time for all the variables to affect your area. But every day into the future you're trying to predict is going to be less accurate because more and more variables have to be accounted for.