With concern over how far inland Hurricane Matthew's effects might reach, many people are focusing today on a few of the 20 models on a spaghetti model chart because they are more intriguing and a somewhat bizarre worst-case scenario. If you've seen or heard about it, you know I'm talking about the few that show Matthew turning east into the Atlantic and then circling back around and taking aim at Florida again next week.
While some weather forecast models are better than others, I want folks to really understand that all have their strong points and shortcomings.
Numerical Weather Prediction takes observations and proven mathematical theory and combines them with a few educated assumptions to get output that can be translated into the forecast models like the ones we as a public are used to seeing.
A model's accuracy depends heavily upon the correctness of the input, and each model can have a slightly different set of initial conditions, assumptions, and weighting of math formulas. An error in the initial data, math, or assumptions will be amplified with each time increment in the output. A small error in the model run for this afternoon could become a large error in the same model run's output for three days from now.
A trained meteorologist has a grasp on the strengths and weaknesses of the various models and an understanding of statistics, and he or she uses that knowledge to make his or her best forecast.
In the case of tropical weather systems, the National Hurricane Center employs meteorologists who specialize in understanding those models as they relate to forecasting tropical storms and hurricanes. They are truly experts in the field, which is not to say that the only experts in the field work at the NHC. It is to say that they have possibly the largest concentration of experts in hurricane forecasting in one building. All of whom know that to make a good forecast all of those models on the spaghetti map need to be considered carefully.