@tsjjs2
The app doesn't display the actual temperature, but rather the temperature forecast by a weather model. Therefore, there is usually a slight discrepancy with the local reading. However, under certain conditions, such as in mountains, near the sea, or in a large city, weather model forecasts can display systematic errors due to a lack of granularity, in a situation needing a higher model resolution.
Another source of error can come from the temperature sensor itself, especially if it is insufficiently protected from the sun, near a wall or above a concrete ground.
For a more thorough analysis, could you specify your location?
Have you tried all the models that Windy offers? Using the Compare feature?