Forecasting 101: All Those Crazy Models

I'm sure your television meteorologist has said, "The models are showing that this storm will take this track." But what are these so called "Models" they speak of? Well, I am going to give you a brief over view of the two most common ones used and the one I love the most.

Models are one of the main forecasting tools that Meteorologist use when predicting the weather. Models are a tons of really complex equations that are computed by a super computer. These mathematical equations represent the physical characteristics of a weather system. Each model varies because the initial conditions are different from model to model. The model selects the initial conditions by breaking up the earth into a grid system both vertically and horizontally. This is why each model outputs slightly different results.

The first model I'm going to talk about is called the "Global Forecasting System" or commonly know as the GFS. The GFS is ran four times a day. The GFS is a medium range model because it forecast 16 days from the initial time. Even though it forecast 16 days into the future, it's reliability only is about 7 days from the initial time. The GFS is a good model. It usually goes heavy on precipitation, but overall is a good model.

Above, I posted a picture from the GFS model. It is the winds at the 200 mb level, which is about 40,000 feet above sea level. The areas which are colored in blue are areas of about 60 mph winds and higher. At this level is where you will find your Jet Stream.

The second most commonly used model is the North American Mesoscale Model, or as Meteorologist refer to as the NAM. Just like the GFS this model is run 4 times a day. However, the NAM only forecast three and a half days from the initial time. I think that the NAM does a fantastic job with precipitation. Mainly because it is a short term model. Below I posted another image.

This image is from the NAM model. This is a precipitation forecast map. The areas shaded in green is where the model expects the to be rain falling over a 6 hour period and the amount that will fall. You might have noticed an excessive about of "H" and "L". I like to call it the model gets happy and puts a couple of extra High's and Low's symbols.

The last model I am going to mention, which is my personal favorite is the European Centre for Medium-Range Weather Forecast. On the forecast maps it is abbreviated as ECMWF, but most meteorologist just call it the European. Like the GFS it is a medium range forecast model, providing data for 15 days from the initial time. However, unlike the GFS this model, the European is only ran twice a day. This is my favorite model because from all of my time as a forecaster, when the big storms are coming this model usually is the first to get the correct track of that particular storm.

Just to let you know of a little secret, almost all the tools meteorologist use to make their forecast can be found for free on multiple websites. I've one that I use a lot  is called E-Wall, it is from Penn State. http://www.meteo.psu.edu/~fxg1/ewall.html



Resources:
 http://www.research.noaa.gov/