Why?
It was supposed to be 89°. Then 95°. Then the daily summary reported 100°, and the forecast had quietly moved on with its life. I hadn’t.
This wasn’t a one-off. The forecast kept promising cooler weather was on the way. It was always a few days away, and somehow it never arrived. So I started keeping receipts.
Illustrative example
+11° warmer than the earlier saved prediction, and +5° versus the latest.
For future days, the number shows how much the forecast moved. Once the local day ends, the largest miss compares the modeled daily summary with whichever saved pre-day prediction was furthest from it. Earlier predictions that were never recorded stay missing.
About the receipts
We save daily Apple Weather forecasts as they change, then compare pre-day predictions with its completed-day summary for the same coordinates and local date. The summary is modeled rather than a reading from a specific weather station. Saved history can be partial; missing data is never zero, and a result stays unavailable when either side is missing.