Question: I’ve been seeing a lot of what they call “spaghetti maps” this hurricane season. I get that it shows the different possible paths a hurricane can take, but they never really explain much about how they are made. I’m hoping you can provide some more details. Thanks. — RT, Fort Meyers, FL
Answer: Sure thing RT. But first, you really need to understand what a weather model is. There’s a great explanation in my July 15, 2019 post you should go back and read. You probably heard some meteorologists use that term when describing “spaghetti maps” (officially called ensemble maps).
The graphic above is a snapshot of the Atlantic on Sep 12, 2023 (when I wrote this post). It shows four storm systems then being tracked by NOAA: hurricanes Lee and Margot, and tropical depressions INVEST98L and INVEST97L. The “INVEST” means they haven’t been named yet but are under INVESTigation.
Every colored strand in that ensemble map represents the path predicted by a different model. Each is the result of a lengthy simulation run on a supercomputer. Most are done by government agencies like our NOAA, and the EU’s ECMWF, but there’s an increasing number of private organizations joining the mix, some with their own weather satellites.
Not surprisingly, the various models do not agree exactly with each other. The data fed into the models, and the factors considered by the models, and the equations used in the models, are not the same. In fact, many of the models incorporate Monte Carlo methods to allow for the random aspects of weather. And individual models are often run multiple times until a “consistent average” emerges.
The ensemble maps you see on your local weather channel are prepared by in-house graphic designers and only show a few of the model outputs, as in the graphic above. Otherwise the graphic would overwhelm the viewer with too much information — over 100 models are running continuously around the globe. Here’s an ensemble map for the northern jet stream that incorporates almost all of them:
Now that map actually does look like spaghetti. Since the jet stream drives so many other aspects of the weather, there’s a huge interest in predicting what it might do. You can click to enlarge it and see the amazing amount of detail provided. And that’s only the North American part of the full ensemble map.
You’ll never get that level of detail in your local forecasts. Still, it serves to demonstrate the advanced state of weather prediction science. There will always be some uncertainty involved in longer range forecasts, but the science is getting better every day. That’s largely thanks to increases in computing power, and more comprehensive global data acquisition from satellites.
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