It sounds like your device has moved the app into power save mode. The first thing to check is to see if updates are being suppressed in the background, which could lead to old information.
Go into your device settings to applications, to 1Weather, and then tap "Battery"- are any of the power saving options on in that location? If so, turn them off (1Weather will use very minimal battery and data when in the background, but if the system is allowed to fully shut the app down, updates will cease).
Next, go to settings --> Battery is 1Weather optimized under App Power Monitor? If 1Weather is listed under monitored apps, try moving it into Unmonitored apps and see if that helps.
Usually if the app, clock, or widget data isn't updating in a timely manner, it's due to the app getting shut down in the background by one of the Android power saving services (PowerMonitor and Doze), which are very aggressive on newer Android versions.