Here’s a typical screenshot of Apple’s Weather app. It shows the current temperature and the forecast for today’s high and low temperatures. (Let’s ignore all the other data for the moment.)
Notice anything? Today’s “low” is predicted as 43º, and the high as 61º. Yet it is currently cooler than the low: 41º. Plus, no single hour of the day is expected to actually reach the high of 61º. By the end of this day, the hourly forecast was proven correct: at no point did it get warmer than 57º.
In my world, the app would currently be showing the low of 41º, and the high of 57º (assuming there isn’t some quarter-hour stretch where it will shoot up to 61º before dropping back down to 57º by the end of the hour, which seems rather unlikely.)
Apple’s app gets its data from Yahoo weather, but I’m sure I’ve seen this behavior in many other weather apps, websites, etc. They show the historical predictions for the high and low, failing to update them as the actual data comes in. If the low was predicted as 50º, it doesn’t matter if a freak storm should drop the temperature to 32º—the app still claims that “today’s low will be 50º.” The app is lying.
I’m tempted to believe that this nonsensical tradition of sticking to the obviously wrong predictions for the day’s high and low temperatures is some kind of professional-pride thing, like the meteorologists feel honor-bound to report their original guesses, right or wrong.
As a user, I really don’t care what was originally calculated. It seems obvious to me that if it’s currently cooler than you predicted it would ever be today, then that's today's low temperature. I admit it's possible there's some specialized reason to show the old forecast, but heck if I know why.