tldr: for the best US consumer weather forecasters the mean error on high/low temp for 1-5 day forecasts is around 3F and they hit within 3F within 70% of the time.
7-day has declining accuracy and 10-day is not much better than statistical analysis on historical trends.
You can also check accuracy for your local zip code (in US) at: https://www.forecastadvisor.com/
tldr: for the best US consumer weather forecasters the mean error on high/low temp for 1-5 day forecasts is around 3F and they hit within 3F within 70% of the time.
7-day has declining accuracy and 10-day is not much better than statistical analysis on historical trends.