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Active Weather: Explaining the Science Behind the Forecast

Meteorology 101: We’re heading into a more active period of weather over the next 5-7 days; I believe in explaining the science behind the forecast. So here we go. Below, you’re looking at the European Ensemble Forecast over the next 15 days for Raleigh as an example. As you can see, there are a lot of numbers, and each horizontal line represents an ensemble member.

What are Ensembles?

Models run ensembles with the main operational run; ensembles are the best way to predict weather accurately. However, many people don’t like showing them because they’re confusing for the public. What happens with an ensemble run is that, for example, the European model has 50 ensemble members, and each member runs, but the starting atmosphere is slightly altered. This helps models predict the atmosphere better, because Earth is so large we can’t get data everywhere 24 hours a day. So, computers predict some changes in the atmosphere, which can impact storm systems. While you’ll see all these ensembles, some have significant variations at times, which are outliers. So, this helps forecasters make the best forecast.

Looking at the latest ensembles from the European model run, all 50 members show at least 1”, and more than 90% of the members show over 3” of rain expected in Raleigh over the next 7 days, with some showing locally higher amounts.

The Bottom Line: Rain is coming a few showers tonight across the state, widespread rain is likely Saturday statewide, and another robust storm system is expected Tuesday that will bring several inches of rain. Get your rain gear ready!



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