Weather models get a lot of screen time during hurricane season- in fact you probably know a few by name!
Different models come up with different tracks- but why? To do that, I have to explain how a weather model creates a forecast.
Contrary to what some people think, a forecast isn’t made by looking into a magic ball but by complicated equations. These equations, created years ago and learned by meteorologists in college classes that still give me nightmares, explain the atmosphere all around us. Velocity, vorticity, advection- phrases you might have heard a meteorologist use when explaining a forecast are derived from these equations.
These sets of equations explain the atmosphere- and by solving them you could create your own forecast! The problem is nobody has the time, paper, and patience for that. Once you solve one set of equations with an initial set of observations, you’ll have to take your answers and do it all over again and again for every block of time . Thankfully we have computers which do the heavy lifting for us. And I mean heavy, as weather models require some of the most complex supercomputers in the world.
These weather models take in massive amounts of information gathered from observations, then plug those numbers into the equations, and then solve them over and over and over for every location they cover for time periods ranging from hours to days!
So if weather models take in the same information and solve the same equations- why do they often come up with different solutions?
A couple reasons. Though weather models use the same fundamental equations, they take different approaches to solving them, with various assumptions leading to different results.
For example, assuming that the force of decreasing pressure with height is NOT equal to the force of gravity allows for higher resolution weather models able to forecast smaller storms, like we see in the summertime.
Different models also handle geography differently, performing better or worse over mountainous or coastal areas. Finally, though there are a lot of weather observation sites to create those initial conditions needed to solve those equations- there’s still a lot of holes (like the ocean) where we don’t have valuable info. So models have to fill in the gaps by, you guessed it, more assumptions.
Despite all of this, weather models do their job wonderfully, illustrating the insanely complex atmosphere.
Storm Team 2 Meteorologist David Dickson