For myself, I don't rely on too many models, because it just causes confusion in my mind. It's like the old adage, "the man with one watch knows what time it is, but the man with two watches is never sure." I primarily consult the NVG model (a baroclinic model, and thus more likely to be accurate), but also look at the GFS model (a barotropic model, which makes it less accurate, but which runs further out in the future - 16 days!) Actually, I don't know where to get the European model results, but it's another baroclinic model, and no doubt good, but it might conflict with the NVG model, and thus cause dissonance. Some weather forecasters have time to consult with a full ensemble of model results, but I don't want that. What I want is to intuitively feel what is making the hurricane move the way it does. There are usually several forces at work, any one of which can make the hurricane move, and which force dominates is usually a matter of timing. Which force is first? Which force is strongest? Do the forces trade off? Understanding that trade off is more important than having multiple model results. The model results usually vary from one another anyway because the timing of force changes are modeled to be slightly different. So, the models all have their strengths, but need not all be accurate.
The Hurricane Center uses what it considers to be the top models for forecasting hurricanes. The models come from different countries with their own weather services, and some come from the United States, which has multiple agencies that have their own weather models for their own purposes: the National Oceanic and Atmospheric Administration, the National Weather Service, the Navy, NASA and more.
But the two we hear about most are an American model known as the Global Forecast System, or GFS; and the European model or the ECMWF, which is the European Center for Medium-Range Weather Forecasts. The two global models are considered the best in the world, and are often pitted against one another.
Experts generally agree the European model has an edge over the GFS, Rood said.
Both are modeled from equations performed by high-powered computers. The GFS and the European both are medium-range forecasting models and can forecast fairly far into the future. The Euro can forecast 10 days out, while the GFS can model 16 days out.
These two models, along with all the others, have the opportunity to use the same shared data in their model runs. Yet, they result in different outcomes.
“Just because they have the opportunity doesn’t mean they are all starting with ... the same data,” Rood said. “The other thing is, they all use the data in a little bit of a different way, so they have different algorithms.”
The main difference in the models is “data assimilation,” which essentially means how the models start. Scientists use different methods to begin these assimilations, which gives them different results. Rood said the European model generally has a better assimilation process than the GFS, which can at times lead to more accurate models.
The same models can also be run about 30 to 50 times to make what’s called an ensemble. Slight tweaks to the information used in the same model can result in dozens of different tracks. While it may look overwhelming to the untrained eye, these ensembles are helpful for forecasters.
Outside of the models that are used for everyday weather, there are exclusively hurricane models that focus on a much smaller area where a storm is located. These models are good at gathering more details like wind speeds and have become another piece in a forecaster’s tool belt.
“From a forecaster’s point of view, there is an advantage of having multiple models, because it helps them to better understand the uncertainty,” Rood said.
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