When in Trader Joe's

To celebrate the weekend, I visited Trader Joe's at 72nd street. When I went there around 6PM, the store was packed with people. What surprised me was that a lot of groceries didn't run out then--last time I visited, it was around similar time on a Tuesday and a lot of items were already sold out by then. I thought about how statistics must be important for Trader Joe's, because they have to make predictions about inventories. I'm sure the day of a week must affect daily sales (more customers on weekends who stack up groceries for the week ahead) but there should be other factors that can be used to predict sales. It must be important to make a good prediction, otherwise they might lose potential sales when items run out fast or end up having too much produce on their inventories that will go bad.