Wednesday, December 19, 2012

Long Range Forecasting Is Tough

When we make forecasts for 24-72 hours out, it is typically very accurate. To show you the difficulty of forecasting, I want to show you what we call "Ensemble" maps. Ensemble forecasting is a technique that takes several different datasets in attempt to obtain a representation of a storm system or pattern. Below is the GFS Ensemble spaghetti plot for 24 hours from now. It looks nice, neat, and in order. Forecasting 24 hours out, is not too difficult. The blue lines are the 540 decameter 500mb lines. (Roughly, the rain/snow line in a perfect world). It's pretty easy to point out the troughs (u-shaped features) and ridges.
If we look at the ensemble for 7 days out, it looks much different. Sure, the "mean" lines are plotted, but I think it is clear that the accuracy is much more suspect! I can even show these two images to my kids and ask which one looks less believable and they would say the 7 day Ensemble map.
I did not want to go in depth about Ensemble forecasting, but I did want to visually show you that nailing down a severe weather event or snow storm 7 days out is challenging. This is why we always say to "stay tuned for updates!"

We'll continue to try our best to nail the forecast, 7 days in advance!


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