Why is the weather forecast always wrong?

You know what I’m talking about. You’ve planned the beach trip for days. Took forever to organise between your friends. Towel packed, sunscreen on, only to arrive to 20 degrees, overcast, and storm clouds in the distance. Why can’t those guys at the weather station do their *** job right???


At least, this is what happened to me on the weekend. But before cursing the meteorologists responsible, I had to take a moment and remember that they, too, are simply scientists just trying to make the most accurate predictions they can with the data they’ve got. This is known as scientific modelling, and we use it to make millions of predictions every day.


Modelling is inherently uncertain


One of the most quoted aphorisms in science is the statistician George Box’s assertion that “All models are wrong, but some are useful.” Models are effectively our way of trying to describe and predict something in theoretical terms that exists in real terms. This means that any given model will be based on two fundamental flaws – first, that we can only include a finite number of variables, and second, that our measurements of these variables are bound to have an element of error to them. And for the atmospheric systems that meteorologists study, small errors can have big consequences.


The butterfly effect


One butterfly flaps its wings and alters the course of the universe. That’s how the theory goes right? Well, not quite. The butterfly effect actually has its roots in meteorology, where a scientist named Edward Lorenz found that if he rounded his original data slightly differently, his weather predictions based on that data changed dramatically. Now, weather models are created with the help of near constant streams of data from observation points across the surface of the earth and extending up into the atmosphere. If each of these observations are only 99.99% accurate, all of those 0.01% add up, leaving a lot of space for unseen butterflies.


Weather data is real-time


On top of the possibility of high error rates, weather forecasters have to bring us the *most up to date* forecast possible in order to be accurate. This means that their computers are continuously pumping out new predictions in response to the real time data they are receiving. These predictions still need to be interpreted before they are broadcast however, and as such by the time they are broadcast weather forecasts are likely to be either slightly out of date, or the result of a very hasty human interpretation (which, we all know, is one of the biggest source of error in the world).


We are much better than we used to be


Having said all of this, weather prediction is far more accurate than it was when Lorenz was waiting 20 minutes for his 1950s supercomputer to process his data that was accurate to within 750km2. With the wealth of data inputs and incredible processing power of today’s computers, our ability to forecast will only increase as technology improves.


We often take for granted how often the weather report is actually correct, and instead only notice when it isn’t. But in the end, I’ll bet you still checked the weather before you left the house today didn’t you?

One Response to “Why is the weather forecast always wrong?”

  1. Megan Young says:

    i can definitely relate to this, i find it so annoying when the weather is not what it is forecasted to be, i guess from living in melbourne though i’ve come to expect it 😛 i really liked this post, i would say maybe include some photos though?