I think 10 days is basically the normal term for weather, in that we can get decent predictions for that span using "classical"/non-ML methods.

To be clear: With short-term I meant the mentioned 6 hours of the article. They use those 6 hours to create forecasts for up to 10 days. I would think that the initial predictors for a phenomenon (like a hurricane) are well inside that timespan. With long-term, I meant way beyond a 14-day window.