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Comment by ars | Hacker News Reader

> East Coast US was accurate to 3 to 5 days

Interestingly in the US, the East Coast forecast is more accurate than the West Coast.

This is because the trade winds in the US mostly move West to East, so most of the Weather moves in that direction as well.

There are more weather sensors on land then in the Sea, so there is more data available to make a forecast with.

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I would be interested to see a global heatmap of weather predictability.

It's not just about the number of sensors. The clouds form over the sea. Predicting when and where those clouds will form is much harder than predicting when and where those clouds will move.

Clouds form over land too.

When warm wet air meets cool air you get clouds. The goal is being able to measure the humidity and temperature of those colliding air masses.

One needs to account for relative humidity, which the ocean provides. Much of the US landmass between the pacific crestline and the rocky mountains is arid desert (from the canadian border to mexico). Second, there exist ocean-specific dynamics like el-nino, which don't really have an overland anolog.

As a life-long east coaster, I never understood the frequent grouses one hears about weather reports being inaccurate. I consider them to be quite good given how much inherent chaos is in the system they're trying to predict.

And, up until the last year or so, there were parts of the west coast (basically, off the olympic peninsula) that didn't have any offshore radar coverage. So there were certain classes of dangerous storms that could sneak up and whack Seattle. (One of the storms that did in a floating bridge did this, basically, no one knew that there was a hurricane force storm until it hit the coast, and from then, it was an hour to Seattle)

> This is because the [westerlies] [...] move West to East

FTFY

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