10 August 2014

## How Weather and Climate Models Work- or Why Meteorologists Learn Calculus

Posted by Dan Satterfield

Numerical weather models have come light years over the  last 30 years, and despite what you may think, they make it possible to make very accurate weather forecasts for as much as 5-7 days into the future possible. Have you ever wondered just how they work? It’s not something that you can cover in a few paragraphs, but it is not all that hard to get a basic understanding of how it’s done, and if you will give yourself 50 minutes and pay attention, you will (I hope) find it very fascinating. You will also not just see greek when you see an equation like this somewhere! (see below)

If you have not had differential calculus this probably looks like greek, but of you watch the video below it will make much more sense. Click for larger version.

Let me show you how good the numerical models can be. The two images below are the water vapor satellite images from Goes East and West at 03 GMT Sunday 10 August (11 PM Saturday night U.S. East Coast time.

Same time looking at the western U. S. 6.9 micron ir wavelength.

Now below is another image made by the NSSL WRF weather model. It was a forecast made at 8 PM Friday for the same time (12 AM EDT Sunday).

This is a numerical weather model forecast made 28 hours before for the same time as the actual satellite image above.

If you spend some time looking and comparing, you will see that overall the model forecasted thunderstorms and moisture channels quite well. It even has the position of the big upper level low off San Francisco just about right on.

How can we do this??

Math and physics.

Watch Dr. Margot Gerritsen of Stanford explain in the video below. She gets into several other subjects, but watch the video thinking about variables such and pressure, humidity, and temperature, and you will end up 50 mins. later with a good idea of how numerical weather models (and climate models) work!

Oh, and any high school girls watching? Margot is a she. Science is not just a guy thing!