It ain't over 'til the fat lady sings. – Modern Proverb
When is it too late to update a forecast?
Here's a theoretical scenario. You're a retailer who sells barbecue charcoal. The July 4th is approaching and a large spike in sales is predicted for that week.
Time marches on and now you're at the beginning of the week in which the holiday is going to happen. For a large swath of the country, a large storm front is passing through and there's no way in hell that people will be out barbecuing in their usual numbers.
Remember, the holiday is only a few days away now. Chances are that the stores have already received (or have en route) a large amount of charcoal based on the forecast that was in force when outbound shipments were being committed to the stores.
So, we're already within the week of the forecasted event and most (if not all) of the product has already been shipped to support a sales forecast that is way too high. Nothing can be done at this point to change that outcome.
So changing the forecast to reflect the expected downturn in sales is basically pointless, right?
When the entire supply chain is linked to the sales forecast at the store shelf, then the purpose of the forecast goes far beyond just replenishing the store.
The store sales forecast drives the store's replenishment needs and the store replenishment needs drive the DC's replenishment needs, and so on. All of this happens on a continuum that really has nothing to do with what's already been committed and what hasn't.
If your sales forecast for charcoal in the affected stores is 5,000 units over the next 5 days, but you know with a pretty high degree of certainty that you will only sell about 2,000 because of the weather, then why would you delay the process of realigning the entire supply chain to this new reality by several days just because you can't affect the immediate outcome in the stores right now?
The point here is that while the supply chain is constrained, the sales forecast that drives it is not. It may not be possible for a forecast update to change orders that are already en route, but it is always possible to change the next planned order based on the new reality. In that way, you already have a plan in place that is starting to get you out of trouble before the impact of the problem has even fully materialized. In other words, bad news early is better than bad news late.
If you have information that you think will materially impact sales, then the only time it's too late to update the forecast is after it's already happened.