Why Weather Forecasts Are So Difficult

There was some kvetching on the radio this morning about the missed forecasts we've had this month, especially with snow coming today, and it just annoyed me.

This is one of my pet peeves, and it was so even before I headed down this career path. It's also one reason (of many) I don't want to go into forecasting.

Try this at home. I dare ya:

- Take a huge not quite spherical ball.
- Cover it with a very irregular surface, about 3/4 of which is water.
- Cover that with a thin mixture of gases that gets exponentially thinner as you go up from the surface.
- Tilt it 23.5 degrees, with a bit of wobble.
- Spin it.
- Heat it irregularly via a huge ball of fusing gas about 93 million miles away.
- Send it around that ball of gas in an elliptical orbit so its distance to the heat source changes.
- Accurately tell me what all the gases covering the first ball are going to do at any given time and place in the future.

Go on.

The other problems?

1. We know the set of mathematical equations that describe how that mix of gases flows around the big ball, with and without varying amounts of water vapor. Unfortunately, that set of equations cannot be solved exactly by any known means.

So the forecasters build models that make approximations. Approximations introduce error. What a concept.

2. We don't have accurate observations in enough places or often enough. I've heard via a third party someone (on faculty here at Purdue, supposedly, but I don't know whom) theorized that if we had observations about every square kilometer and every 300 meters in altitude through the troposphere (the bottom 11 km or so), we might have enough observations to calculate the models accurately.

Forecasters make mistakes. Now you know why.